in the lymph nodes and vessels of cats, dogs, and primates. The parasites in this .... 500 eggs (nits) on the horse's forelegs, nose, lips, and body. The larvae ...
A-Z OF PARASITOLOGY
A–Z OF PARASITOLOGY
A G Arijo
A. G. Arijo
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Forward Althoug, there are many sources that may satisfy a student, but books have specific importance that may never ever be dropped down. In Pakistan, there is sever paucity of quality books and those which are available are quite expensive. Present effort is aimed at publishing a book that students of parasitology may use as squik refence. This book provides a concise and clear knowledge about Parasites and Parasitology at very affordable price. Entire material is given in alphabetical manner to enable students use this book in easy way. I must admit that, some material incorporated in this book was taken from many source, edited and added for better understanding. I am confident that, students will k quick knowledge and this hubmle effort will be appreciated.
Author
Note: All rights of this book are with Dr. A. G. Arijo, B-58, Indus Bungalows, Mir Hassanabad, Hyderabad.
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Alphabet A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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from 4
To
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A ACARICIDES Chemical compounds which are used to kill ticks and mites are called acaricides. Some very active acaricides, active against ticks and mites are chlorinated hydrocarbons, organophosphorus compounds, pyrethroids, carbamates, rotenone, sulphur compounds, benzyl benzoate, and ivermectin. Acaricides are generally applied in the form of dips, washes, sprays, powders, Pour-ons, or injections. The method of application varies in different animals depending mainly on their age, size and nature of parasitic infeciton. ACARINA It refers to an order of class arachnida which includes ticks and mites. The body of ticks and mites is divided mainly into two parts i.e. cephalothorax and abdomen. There are four pairs of legs and mouth-parts which are modified for biting, sawing, piercing, and sucking. The eggs, which are laid in thousands, hatch into larvae with three pairs of legs. The six leged larvae later on develop into into sexually immature nymphs which resemble the adult except that they are smaller in size. All ticks and mites are mostly ectoparasite of livestock, poultry, pets, and humans. They feed on the blood and tissue fluids of their hosts and are responsible for transmitting a large number of diseases such as Babesiosis, Anaplasmosis etc.
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AMBLYOMMA It is a genus of hard ticks, which are ecto-parasitic on all domestic animals and some times on man. The bites of soft ticks generally produce sores and some species transmit the rickettsial organisms that cause heart-water in cattle and Q-fever in cattle, sheep, and goats. Amblyomma ticks on animals are controlled by dipping the animals in acaricides. AMOEBIASIS It is a disiease of animals and humans, caused by protozoan parasite Entamoeba histolytica. The infective cysts of parasite parasites reach the hosy intestine through contaminated food and water. On excyctation in intestine, the trophozoites are released. These trophozoites settle in the lumen of intestine and cause dysntry. ANAPLASMA It is a genus of single cellular parasites found within red blood cells of various animals. The genus includes three species which cause a disease called anaplasmosis in domestic animals. A. marginale is characteristically located on the margin of the red cells of host. A. centrale causes a milder disease in
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cattle and the organisms reside in the centre of the red cells. Both the species of parasites are transmitted to the domestic animals by ticks. ANAPLASMOSIS It is a disease of cattle, buffalo, sheep and goat caused by parasites belonging to genus Anaplasma. The disease is also called as Gall-sickness. It occurs in tropical and subtropical regions and is transmitted by a variety of bloodsucking insects in general and ticks in particular. It can also be transmitted by the transfer of infected blood in transfusions or via contaminated needles. The parasites destroy red blood cells causing anaemia, fever, and jaundice. Our research reveals that the disease is common in cattle and buffaloes in Hyderabad Sindh. Animals that recover remain infected but immune for rest of their life. The disease may be treated with tetracycline antibiotics, however vaccines are also available. ANCYLOSTOMA It is a genus of parasitic nematodes occurring in the small intestine of cats and dogs in tropical and subtropical countries of the world. Worms belonging to this genus are small and stocky. The adults attach to the mucous membrane and suck blood, causing a chronic and debilitating condition in their host. At post mortem, the mucous membrane can be observed almost white which is due to loss of blood. A. caninum and A. tubaeforme are common examples in cats, whereas, A. braziliense can infect humans where it can cause creeping eruption due to larval activity under the skin. Eggs of these worms are passed in the faeces, where they develop into infective larvae. The other host becomes infected either by A. G. Arijo
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ingestion, or by penetrating the skin and migrating to the lungs, where they are carried up to the wind pipe and swallowed again. The larvae are vulnerable to desiccation, and may be controlled by keeping the houses clean and properly drained. Infected animals can be treated with bephenium or benzimidazole compounds. ANGIOSTRONGYLUS It is a genus of parasitic nematodes containing A. cantonensis, which is mainly found in rodents, but may also infect humans. The larvae of A. cantonensis migrate to the heart, and may reach the brain via the carotid artery. These parasites feed on the meninges and cause a condition called eosinophilic meningoencephalitis, which is characterized by the formation of granulomatous tissue around the parasite worm. This parasite uses snail, freshwater prawns, oysters, and slugs as intermediate hosts. Humans are generally infected by eating raw prawns or vegetables contaminated with the larvae.
ANTHELMINITIC Chemical compounds that are used to kills helminth parasites are called anthelmintics. Anthelmintics are further divided into various names depending on their their effectiveness against the different types of helminths: for example nematocides have activity against nematodes (roundworms); cestodicides are against tapeworms; and flukicides are used to kill trematodes. A best anthelmintic is a drug which should have following qualities. (1) Kill the parasites effectively without causing toxicity to the host, (2) Should have a broad A. G. Arijo
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spectrum efficacy against adult and larval stages of the parasites, (3) Should be easy to administer, (4) Must persist in tissues long enough, and (5) Should be cheap in price. Anthelmintics may be administered orally as tablets, pastes, drenches, incorporated in feed or water, or given as slowrelease. Soluble preparations can be injected. A topical pour-on preparation such as levamisole is also available. Some compounds with a broad spectrum of activity include the benzimidazoles, ivermectin, levamisol, nitroscanate, pyrantel, morantel, and organophosphorus compounds. Other compounds with a narrower spectrum of activity include piperazine, diethylcarbamazine, bephenium, bunamidine, diamphenethide, clorsulon, niclosamide, oxyclozanide, nitroxynil, brotianide, rafoxanide, praziquantel, phthalofyne, and thenium. ARACHNIDA It is a class of phylum arthropoda which includes the ticks, mites, scorpions, and spiders. The body of arachnids is divided into two regions, cephalothorax and abdomen. The cephalothorax which bears four pairs of appendages is only 5 percent of total body whereas; abdomen is 95 percent of the whole the whole body. The arachnids lay eggs which hatch into a nymph which attends the adult size after regular feeding on host.There is no pupal stage. The arachnids of veterinary importance are ticks and mites which are parasitic in nature and are source of diseases transmission in live stock, poultry and pet animals ARGAS It refers to a genus of soft ticks. Soft ticks are ecto-parasites of birds, especially domestic fowls, but may also bite A. G. Arijo
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humans, horse, cattle and buffalo. The adults and nymphs are mostly found either in the nest or around the nest and wait to suck the blood at night while the host is asleep. The larvae remain attached to the host for 5-10 days. The adults can survive for 5 years without feeding on host. A heavy infestation of soft ticks causes intense irritation, anaemia, and even death. The moderate infestation leads to the loss of health and a reduction in egg production. The soft ticks are reported to transmit the protozoan and bacterial diseases, such as fowl spirochaetosis. ARGAS PERCICUS It is a very common parasitic species of soft ticks belonging to genus Argas. In Sindh, province of Pakistan, this species of soft ticks is quite common and cause of reduction in egg production in poultry birds. These ticks are better controlled by using acaricides in the form of dusting powder. ARTHROPODA It refers to the largest phylum of invertebrate animals which include 80% of the total animal fauna. Arthropods have a segmented body and a hard exo-skeleton. The growth occur by moulting and at each moult, the old skin is removed and replaced by new one. Each body segment has a pair of jointed appendages (legs) which can function variously as mouthparts, legs, wings, gills, sense organs, or reproductive organs. The phylum includes the crustaceans, arachnids, insects, centipedes, and millipedes. Many are of great veterinary importance, especially the mites, ticks, and flies.
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ASCARIS It refers to a genus of parasitic nematodes. Parasites in this genus are frequently found in mammals (including humans), and in domestic chicken. Ascaris lumbricoides, in humans and A. sum, in pigs are very popular parasites of this genus. In host body, these parasites are found in the lumen of small intestine where they may grow as long as 20cm. The lifecycle is direct and does not involve any intermediate host. The eggs, which are cream to light brown in colour, are passed in feces. Mostly the larval development takes place within the eggs. Larvae are ingested by the host during grazing on open pastures. The larvae migrate from digestive system to the liver and the lungs. In young host, the passage of the larvae through the lungs can cause a serious form of pneumonia durig which animal may show coughing, distressed breathing, weakness, and general weakness. The migrating larvae of A. sum damage the liver in pigs, causing milkspot liver. Heavy infections can cause enteritis and even complete blockage of the digestive tract. Control of this ascaris parasite may be achieved by cleanliness in housing and avoidance of contaminated areas. In affected animals the anthelmintics such as fenbendazole, thiabendazole, ivermectin and dichlorvos are effective against adult the parasite. ASCARIASIS Ascariasis is the most common helminthic infection, with an estimated worldwide prevalence of 25% (0.8-1.22 billion people). Usually asymptomatic, ascariasis is most prevalent in children of tropical and developing countries, where they are perpetuated by contamination of soil by human feces or use of untreated feces as fertilizer. For more information on ascariasis in children. Symptomatic ascariasis may manifest as growth retardation, pneumonitis, intestinal obstruction, or hepatobiliary and pancreatic injury. Ascariasis may exist as a zoonotic infection associated with pigs and use of hog A. G. Arijo
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manure, But, in most endemic areas, it is most likely transmitted from person to person or animal to animal. ASCARIS LUMBRICOIDES One of the very common nematode species that parasitize humans and animals. Ascaris lumbricoides is the largest nematode (roundworm) parasitizing the human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30 cm.) Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces . Unfertilized eggs may be ingested but are not infective. Fertile eggs embryonate and become infective after 18 days to several weeks , depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed , the larvae hatch , invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed . Upon reaching the small intestine, they develop into adult worms . Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years. ASUNTOL Trade name for the organophosphate compound used against ticks and mites that infest on livestock animals. Asuntol may also control blowflies, lice, and keds and has a residual effect lasting for up to 20 weeks. Special attention is demanded while treating the infested cases as the improper A. G. Arijo
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dosage of asuntal may produce toxicity which is characterized by salivation, laboured breathing, stiffness, diarrhoea, and muscle tremor. However, if the toxicity develops, animals be treated with Atropine sulphate. AVIAN MALARIA A type of infection caused by Plasmodium, Leucocytozoon, and Haemoproteus. The infection is important in tropical countries, where a large number of domestic and wild bird species are affected. The life cycles, diagnosis, treatment and control of these parasites and the disease is more or less same as that of human malaria.
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B BABESIA A genus of protozoan parasites. Babesia species are blood parasites. Members of this genus are known as tick-borne parasites of domestic animals and wild rodents, and responsible for causing Texas Cattle Fever and Malignant Jaundice of dogs. Human infections are rare but have been documented worldwide. Each species of Babesia is specific to a particular host species. The organisms range in size from 1 to 2 μm and vary from circular to pear-shaped, mostly occurring in pairs. During the initial stages of infection, the parasites divide in red blood cells and invade non-parasitized cells until 10% or more of red blood cells are infected. In animals that recover from the infection of babesia, parasite number falls until they are no longer easily detected in the blood. They persist in low numbers in the circulation for the life of the host, evading the host’s defences by exhibiting antigenic variation. At this stage they usually cause no harm but are a potential source of infection for other animals. When ticks feed on the blood of an infected animal, the parasite multiplies in the tick and invades many of its tissues. It is transmitted via the salivary glands of either the same tick, or in the case of a female, its larval offspring. There are several Babesia species responsible for disease in cattle, with different geographical distributions. B. divergens affects cattle in North Western Europe and is transmitted by the sheep tick Ixodes ricinus. In tropical regions of Africa and South America, the major cause of A. G. Arijo
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babesiosis is B. bigemina, transmitted by Boophilus spp. B. bovis is another tropical species with a similar distribution and is the chief pathogenic species in Australia. B. canis parasitizes dogs in tropical regions. Additionally, there are species of Babesia causing disease in horse, sheep, pigs, and cats. BABESIOSIS Babesiosis is caused by intraerythrocytic protozoan parasites of the genus Babesia. The disease, which is transmitted by ticks, affects a wide range of domestic and wild animals and occasionally people. While the major economic impact of babesiosis is on the cattle industry, infections in other domestic animals, including horses, sheep, goats, pigs, and dogs, assume varying degrees of importance throughout the world. Two important species in cattle— B bigemina and B bovis— are widespread in tropical and subtropical areas and are the focus of this discussion. However, because there are many common features of the diseases caused by different Babesia, much of this information can be applied to other species. Transmission and Epidemiology The main vectors of Babesia bigemina and B bovis are 1host Rhipicephalus (Boophilus) spp ticks, in which transmission occurs transovarially. While the parasites can be readily transmitted experimentally by blood inoculation, mechanical transmission by insects or during surgical procedures has no practical significance. Intrauterine infection has also been reported but is rare. In Rhipicephalus spp ticks, the blood stages of the parasite are ingested during engorgement and undergo sexual and asexual multiplication in the replete female, infecting eggs and subsequent parasitic stages. Transmission to the host A. G. Arijo
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occurs when larvae (in the case of B bovis) or nymphs and adults (in the case of B bigemina) feed. The percentage of larvae infected can vary from 0–50% or higher, depending mainly on the level of parasitemia of the host at the time the female ticks engorge. Under field conditions, the rate of tick transmission is generally higher for B bigemina than for B bovis. Clinical Findings and Pathogenesis The acute disease generally runs a course of 1 wk. The first sign is fever (frequently 106°F [41°C] or higher), which persists throughout, and is accompanied later by inappetence, increased respiratory rate, muscle tremors, anemia, jaundice, and weight loss; hemoglobinemia and hemoglobinuria occur in the final stages. CNS involvement due to adhesion of parasitized erythrocytes in brain capillaries can occur with B bovis infections. Either constipation or diarrhea may be present. Late-term pregnant cows may abort, and bulls may undergo temporary infertility due to transient fever. With virulent strains of B bovis, a hypotensive shock syndrome, combined with generalized nonspecific inflammation, coagulation disturbances, and erythrocytic stasis in capillaries, contribute to the pathogenesis. With most strains of B bigemina, the pathogenic effects relate more directly to erythrocyte destruction. Animals that recover from the acute disease remain infected for a number of years with B bovis and for a few months in the case of B bigemina. No clinical signs are apparent during this carrier state. The susceptibility of cattle breeds to Babesia infections varies; for example, Bos indicus cattle tend to be more resistant to the effects of B bovis and B bigemina infection than are European breeds. Lesions A. G. Arijo
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Lesions include an enlarged and friable spleen; a swollen liver with an enlarged gallbladder containing thick granular bile; congested, dark-colored kidneys; and generalized anemia and jaundice. The urine is often, but not invariably, red. Other organs, including the brain and heart, may show congestion or petechiae. Diagnosis Clinically, babesiosis can be confused with other conditions that cause fever, anemia, hemolysis, jaundice, or red urine. Therefore, confirmation of a diagnosis by microscopic examination of Giemsa-stained blood or organ smears is essential. From the live animal, thick and thin blood smears should be prepared, preferably from capillaries in the ear or tail tip. Smears of heart muscle, kidney, liver, lung, brain, and from a blood vessel in an extremity (eg, lower leg) should be taken at necropsy. Microscopically, the species of Babesia involved can be determined morphologically, but expertise is required, especially in B bovisinfections in which few organisms are present. B bovis is small, with the parasites in paired form at an obtuse angle to each other and measuring 1–1.5 × 0.5– 1.0 mm. B bigemina is larger (3–3.5 × 1–1.5 mm), with paired parasites at an acute angle to each other. A number of serologic tests have been described for the detection of antibodies to Babesia in carrier animals. The most commonly used are the indirect fluorescent antibody test and ELISA; commercially produced ELISA for B bovis and B bigemina are available. A procedure that may occasionally be justified to confirm infection in suspected carrier animals is the inoculation of blood (500 mL) into a fully susceptible animal, preferably a splenectomized calf, and subsequent monitoring of the recipient for infection. PCR and real-time PCR assays capable of detecting extremely low parasitemias, as occur in carrier animals, and A. G. Arijo
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differentiating isolates have also been described but are not in routine diagnostic use. Treatment and Control A variety of drugs have been used to treat babesiosis in the past, but only diminazene aceturate and imidocarb dipropionate are still in common use. These drugs are not available in all endemic countries, or their use may be restricted. Manufacturers recommendations for use should be followed. For treating cattle, diminazene is given IM at 3– 5 mg/kg. For treatment, imidocarb is given SC at 1.2 mg/kg. At a dosage of 3.0 mg/kg, imidocarb provides protection from babesiosis for 4 wk and will also eliminate B bovisand B bigeminafrom carrier animals. Long-acting tetracycline (20 mg/kg) may reduce the severity of babesiosis if treatment begins before or soon after infection. Zoonotic Risk A small number of cases of human babesiosis have been reported, but the species involved often has not been identified with certainty. Babesia divergens, B canis, B microti, and an unnamed species (WA-1) have been incriminated. Cases reported in splenectomized or otherwise immunocompromised individuals are often fatal. Numerous cases, varying in severity from inapparent infections to acute illness, have been documented in both splenectomized and nonsplenectomized people in parts of North America. These infections were caused by the rodent parasite B microti or an unnamed species (WA-1) whose host appears to be the Bighorn sheep. Human Babesia infections are acquired via bites from infected ticks, or through contaminated blood from an infected transfusion donor. The disease is especially important in cattle, but the research has indicated that it is equally important in buffalo in Sindh-Pakistan. A. G. Arijo
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BALANTIDIUM A genus of ciliate protozoa. The only species of veterinary significance is B. coli, which reach the lumen of the large intestine of host through contaminated water. The partasite is relatively less common in humans, primates, and in dogs. In the lumen of gut, the parasite may cause ulceration. Diarrhoea or dysentery is main and common symptoms. The infection may be avoided by avoiding contaminated water and use of un-washed salads.
BALANTIDIUM COLI B. coli is a member of the phylum Ciliophora, and the class Kinetofragminophorea. It is the only pathogenic intestinal ciliate, and the largest intestinal protozoan parasite causing gastroentrritis. This parasite is found in two forms; trophozoite and cyst. The trophozoite is oval shape and measures 30 to 100 micrometers in length and 30 to 80 micrometers in width. It tapers at the anterior end, where a cytostome is located. Two nuclei are present in trophozoite, a large, kidney-shaped macronucleus, and a small, round micronucleus, located adjacent to the macronucleus. Cilia, which tend to be longer at the anterior end, are present along the border of the trophozoite. Contractile vacuoles are usually present in the cytoplasm. The cytophyge is the excretory pore, and is located opposite the cytoplasm. The cyst is rounded to elliptical and measures 45 to 65 micrometers. A kidney-shaped macronucleus is present, as well as a small, rounded A. G. Arijo
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micronucleus is lying near the macronucleus. Cilia are located within the two layers of the cyst wall, but may be absent in mature cyst. BITING MIDGES The biting midges, “no--ums,” or punkies belong to the family Ceratopogondiae. The most common biting midges are Culicoides spp. They are associated with aquatic or semiaquatic habitats, eg, mud or moist soil around streams, ponds, and marshes. Biting midges are tiny gnats (1–3 mm long) and, like black flies, inflict painful bites and suck the blood of their hosts, both people and livestock. Pathology Culicoides spp are vicious biters and can cause intense irritation and annoyance. In large numbers, they can cause livestock to be nervous and interrupt their feeding patterns. These gnats tend to feed on the dorsal or ventral areas of the host; feeding site preference depends on the species of biting gnat. They fly only in the warm months of the year and are most active before and during dusk. They feed often on the mane, tail, and belly of horses. Horses often become allergic to the bites, scratching and rubbing these areas, causing alopecia, excoriations, and thickening of the skin. This condition has several names, including culicoid hypersensitivity in Canada, Queensland itch in Australia, Kasen in Japan, sweat itch, and sweet itch. Because it is often n during the warmer months of the year, it is also referred to as summer dermatitis. These flies also serve as the intermediate host for Onchocerca cervicalis; the microfilariae of this nematode are found in the skin of horses. Onchocerciasis is a nonseasonal dermatosis that is A. G. Arijo
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similar to sweet itch but usually is less pruritic and affects the head, neck, and belly. These flies also transmit the bluetongue virus in sheep and cattle. Diagnosis Like black flies and sand flies, biting midges are most often collected in the field and not found on the animals. In contrast to the clear, heavily veined wings of black flies, the wings of Culicoides spp are mottled. Identification is probably best left to an entomologist. Treatment and Control Larvae may be attacked in their breeding grounds. Extension entomology personnel should be contacted for the latest approved recommendations. BLADDER WORM It refers to the larval stage in certain tapeworms. A bladder worm is a cyst filled with fluid in which one or more heads of future tapeworm are invaginated. The bladderworms are of three main types: the cysticercus and coenurus of the genus Taenia and the hydatid cyst of the genus Echinococcus. BLOWFLY It refers to flies, which are large in size and found throughout the world near human and animal habitats. Blowflies are reported to cause disease when they sit on the feces and animals. Larvae of these flies are parasites of humans and animals. Some of the important A. G. Arijo
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blowflies are blue-bottle (Calliphora spp.), which normally lays its eggs on meat, the green-bottle fly, the screwworm flies, and the African tumbu fly. All flies are of significant vererinary importance. BOOPHILUS It refers to a genus of hard ticks commonly called cattle ticks. These ticks are mostly found in the warmer countries. The ticks belonging to this genus transmit protozoan parasites, which are cause of babesiosis, anaplasmosis, spirochaetosis, and some bacterial diseases. BOT FLY A group of flies, which include horse bot, sheep nostril fly horse nasal fly, and warable fly. These flies lay their eggs in the skin of host at the site of scratch or skin cut. The larval development cause skin irritation and un-restness in host resulting into drastic rerduction in milk and meat production
BRUGIA It refers to a genus of thread-like parasitic nematodes found in the lymph nodes and vessels of cats, dogs, and primates. The parasites in this genus cause lymphatics blockage due to a fibrous reaction and cause enlargement of the skin and underlying connective tissues. This condition is called elephantiasis in humans. Some of the species of veterinary A. G. Arijo
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and medical importance are B. malayi in cats, dogs, and primates and B. pahangi in cats and dogs. BURGIA MALAIA Burgia malayi are the agents of burgian form of lymphatic filariasis (elephantiasis) found through out Asia. More than 50% of the cases are reported in china and India. The parasite is also reported from Philippines, Thialand, Veitnam, Korea and Japan. There are no confirming reports on the prevalence of this parasite in Pakistan. Mosquitoes mainly transmit the parasite, but humans, cattle, monkeys and other animals may also serve as reservoir hosts. Upon feeding, the female mosquito ingests microfilariae from an infected host. The microfilaria migrates to the thoracic musculature of the insect where they grow and develop into the infective larval stage. The infective stage, which is 1-2 mm in length, moves to the proboscis where it may be released during the mosquito’s next blood meal. In human host, the infective larvae make their way into the periphereal lymphatics, undergoing two molts before they mature in th eregional lymph vessels. This process may take 6-9 months. Adult male and female worms mate and then female worm begins to deposit microfilarae into blood an dare transmitted by numbner of night feeding mosquitoes The parasite produces mild to severe pathologic conditions. The cilical symptoms may begin with in months to years of infection. Lyphadinitis and lymphangitis and lymphatic obstruction are the main symptoms The parasitie may be diagnosed by detecting it in the blood or lymphatic samples. The modern methods are serological tests, including serum IgE titers and antifilarial antibodies. PCR based DNA testing is also available. A. G. Arijo
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The infections with this parasite may be well treated with diethylcarbamazine in conjugation with anti-inflamentary drugs. A single dose of ivermectin has been shown to be effective against microfilaria for up to 6 monthd BUFFALO FLY Buffalo fly are consistently rated as one of the most economically important animal health issues affecting the profitability of beef and dairy industry. The buffalo fly, Haematobia irritans exigua, is a small biting fly 3.5 – 4 mm long. It feeds off cattle and buffalo, and causes irritation which can result in reduced production, if cattle are heavily infested.
Incidence Including Pakistan, India and Bangladesh, buffalo fly are found throughout northern Australia, in north-west Western Australia, the Northern Territory, Queensland and the north-east of New South Wales. In coastal areas of Queensland and far northern NSW, infestations can be present year round. Buffalo fly are less of a problem in southern inland areas ofQueensland and into inland NSW because there are shorter periods of warm wet weather and the winters are colder. Fly numbers in these areas are generally lower during winter with the peak later, often during late summer/autumn. Impact Buffalo flies live permanently on their host, the females only leaving to lay eggs in freshly deposited dung pats. They feed 10–40 times each day and can only live for 1 or 2 days off the host. The life cycle from egg to egg takes less than A. G. Arijo
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14 days under optimal conditions of hot humid weather, but is extended during cool weather. Newly emerged flies king their first host can fly up to 8 km in the search. Movement of infested animals can be an important method of longer distance spread between herds. Buffalo fly infestations vary from animal to animal. Bulls and dark-coated cattle, especially black cattle, m to carry the largest fly burdens. Apart from obvious animal welfare impacts, lower weight gain and lower milk production have been measured in heavily infested cattle. Some cattle are ‘allergic’ to buffalo flies and are intensely irritated by as few as 4 or 5 flies. These cattle scratch and rub themselves constantly, which results in large sores on their necks and sides. The value of the hide is reduced when cattle have developed skin sores as a result of buffalo fly infestation. Some sores present on cattle, especially in the corner of their eyes or on their necks are caused by a parasitic nematode Stephanofilaria stilesi which is transmitted by buffalo flies between cattle. BUFFALO GNAT A common name of blackflies, which are minute in size, black in color and have a humped thorax. These flies are problem nearly in all countries of the world and are frequently found near running water, which is ideal habitat for their breeding. The female flies feed on the blood of livestock and humans with the help of proboscis (a blood sucking mouth part). During breeding season, the eggs are laid under well aereated stones or other objects in the water. The eggs hatch into larvae, which develop into pupae. The pupa is A. G. Arijo
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non-feeding stage. Adult blackflies on emerging out from pupa are very active in the early morning and evening and may attack in swarms, causing cattle to run. Their bite is irritating and very painful. In reaction to these bites, blisters develop at the site of bitting. The animal at this moment rubs its body with any hard object, such as wall or trees, due to which the skin is injured and becomes open to bacterial infection. Black flies are very popular for their role in transmitting the Oncocercaria commonly called River Blindness. Blackflies are also carriers of the protozoan, Leucocytozoon, which parasitizes geese, ducks, and turkeys; it may cause death in young birds. These flies may be avoided by using the insect repellents which are easy to apply and cheap in purchasing. Killing the larvae or pupa with insecticide may disturb the life cuycle of these flies and that is an effective means of control BLOW FLY Blow flies are a diverse group ranging from 6 to 14 mm in length and generally having a metallic sheen to their bodies. The black blow fly has a dark, olive-green body, black legs, and orange pubescence around the mesothoracic spiracles. The secondary screwworm fly also has a green body, but its head is predominantly orange. The body of the green-bottle fly, Phaenicia sericata, is primarily a coppery green with yellowish mouthparts. Lucilia cuprina is a medium sized fly and is mostly a bronze color. All blow flies have blunt mouthparts and do not bite. Egg -- The white or pale yellow eggs of blow flies may occur in small batches or large masses. Individual eggs are about 1.5 mm long, elongate and slightly tapered toward one end.
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Larva -- These white to yellowish maggots have pointed heads. They develop through three instars and become 12 to 18 mm long when fully grown. Pupa -- Blow fly pupa are encased in light brown to black puparia (the tough, hardened skins of last instar larvae). Each puparium is 9 to 10 mm long and 3 to 4 mm wide. Distribution -- The species of blow flies covered here occur throughout the contiguous states and in many other temperate regions of the world as well. Feeding Habits -- Most blow fly larvae feed in carrion or other decaying organic matter. They often infest wounds of sheep, goats, cattle, and other animals. Unkempt sheep are particularly subject to attack. Adult blow flies are attracted to nectar, carrion, garbage, and other refuse and soggy, bloody or soiled hair, fur, or wool. Damages -- Blow flies deposit eggs in castration and dehorning wounds or on dirty, wet wool. The larvae which soon hatch feed on decaying flesh or matted hair. Infested wounds often become inflamed and the hair or wool falls out. Blood poisoning may result. As a rule, most blow fly larvae do not attack healthy tissue. Mature larvae of green-bottle flies, however, have been known to burrow deep into healthy tissue after spending earlier developmental stages in superficial wounds. Fortunately, this particular species is usually of minor importance in North Carolina. Life History -- Blow fly biology varies among species and with environmental conditions so the following information is general. The black blow fly differs from the other two species covered here in that it is a cool weather insect which overwinters in the adult stage and is most numerous in early spring or in autumn. Other blow flies are abundant during the warm, humid, summer months and overwinter as larvae or pupae. A. G. Arijo
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In general, each female blow fly deposits thousands of eggs over her 2- to 8-week life span. Egg masses may consist of 40 to over 1,000 eggs, but the larger masses are usually the result of oviposition by several females at the same location. Incubation may last 4 to 4.5 days, but hatching usually occurs in less than 24 hours when conditions are warm and humid. Depending on temperature and the substrate upon which they are feeding, maggots usually complete development in 4 to 10 days. At the end of this period, larvae typically burrow in the upper centimeters of the soil and pupate for up to a week. Adult flies emerge from puparia and make their way to the soil surface. About 1 week later, females begin to deposit eggs and the life cycle is repeated. Blow flies usually develop from egg to adult in only 10 to 25 days and complete 4 to 8 generations each year. BLACK-WATER FEVER It is a complication of Plasmodium falciparum malaria characterized by the passage of reddish to black colored urine resulting from massive intravascular hemolysis.
BILHARZIA It refers to Schistosomiasis, an infection caused by schistosome parasites such as Schistosoma mansoni, S. japonicum and S. hematobium. The very reason behind the name is the discovery of S mansoni parasite by Theodor Bilharz.
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BOT FLY Bot fly (family Oestridae), any member of a family of insects in the fly order, Diptera, in which the adults are beelike in appearance and hairy but without bristles. The larvae are parasitic on mammals. Horse bot flies (subfamily Gasterophilinae) include species of Gasterophilus, a serious horse pest. The adult horse fly, often known as a gad fly, deposits between about 400 and 500 eggs (nits) on the horse’s forelegs, nose, lips, and body. The larvae remain in the eggs until the horse licks itself. With the stimulus of moisture and friction the larvae emerge and are ingested. They attach themselves to the lining of the horse’s stomach or intestine and obtain all of their nourishment and oxygen from the horse’s alimentary canal. The larvae mature after 8 to 11 months and are eliminated with excrement. In the warble flies (Hypoderma lineatum and H. bovis), young larvae penetrate the skin of cattle and migrate through the body for several months until they come to rest beneath the skin of the animal’s back. There each larva causes a characteristic lump, or warble, from which a cattle grub emerges. The grub becomes a pupa and then a fly to deposit more larvae. BONOSTOMIASIS It refers to disease caused by Bunostomum species, that are nematodes of the small intestine A. G. Arijo
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of ruminants and camelids. Important species include: B. phlebotomum in calves and B. trigonocephalum in lambs. The worms are stout and measure 1–3 centimetres (0.4– 1.2 in) in length. Young animals are most commonly affected and only several hundred worms are necessary to cause morbidity. Adults often carry worms without showing clinical signs. The disease is characterized by Diarrhoea which is the primary sign, along with systemic signs of anorexia, lethargy and weight loss if the worm burden is severe. Hypo-proteinaemia, anaemia and dehydration often occur. Skin involvement due to larvae penetration appears as lesions especially on the feet and limbs. Analysis of faecal samples enables eggs to be found, or adults are visualised in the small intestine at necropsy. All available anthelmintics are efficient at treating the infection. Prophylactic anthelmintic treatment may help prevent the disease, as well as pasture management to avoid egg and larvae accumulation.
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C CANINE BABESIOSIS (PIROPLASMOSIS) A disease of dogs caused by Babesia canis or B. gibsoni, which are protozoons. These parasite are transmitted by variety of hard ticks such as Rhipicephalus sanguineous, Dermacentor spp etc. B. canis is 4-5 μm long, pear-shape, and found in pairs, whereas B. gibsoni is smaller, roughly circular in shape, and rarely paired. Bothe parasites are found in the Rbc of host dog. Canine babesiosis is sometimes a fatal disease. It is found both in acute and chronic forms. Main symptoms of the disease are fever, anaemia, jaundice, and haemoglobinuriay. Canine babesiosis can occur in dogs of any age that are exposed to ticks. The disease may be diagnosed by the finding of babesia organisms in stained blood smears. Although a wide range of babesicidal drugs are available for use in dogs, but a regular treatment of dogs with an acaricide is recommended to prevent the tick infestation on control basis. CARRIER An animal, usually in insect, that transmits infectious organisms from one animal to another. Nosquito for example is carrier of plasmodium parasites. CERCARIAE It refers to the infective larval stage in the lifecycle in trematode A. G. Arijo
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parasites. It develops from redia in the intermediate host, usually a snail. Main feature is presence of tail which helps in swimming. In some trematodes, the cercariae on leaving the intermediate host develops a cysts around by loosing tail and is called a metacercaria, which develop into an adult when swallowed by the primary host during grazing or drinking water. In primary host, the adult trematode (Liver fluke for example) lay eggs which are passed through feces. The eggs hatch into a miracidium which penetrate into snail where it develops into redia and finally cercariae. In certain trematodes, such as Schistosomes, the cercaria penetrate the final host directly through the skin with out converting into a metacercariae. CESTODE They are flatworms or tapeworms which are highly adapted parasites that live in intestine of many vertebrates including man. They can reach several meters in length. An adult tapeworm is impressively simple. It attaches itself to the intestinal wall using scoles and then simple absorbs the digested food gegerously provided by the host. It does not need a mouth, gut or excretory system. Exchange of all material occur over whole body surface. Since the host provides food and protection, the tapeworm is free to concentrate on reproduction. The reproductive capacity of these organisms is incredible; each day several proglottid segments break off and are pushed out of host body in feces. Each proglottis contains thousands of eggs. The life-cycle varies from species to species, but usually involvesan intermediate host, such as cattle, buffalo, sheep, goat or a dog and cat, as well a main
A. G. Arijo
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host. Humans can become infected by eating under-cooked meat that contains tapeworm larvae CHAGAS DISEASE
It is mainly a disease of humans caused by Trypanosoma cruzi. Wild and domestic animals may also become infected, but disease is occasionally reported to develop in dogs. Chagas is a zoonotic disease since T. cruzi is transmitted from animals to humans by blood-sucking bugs. An effective treatment is yet to develop, however, control depends on eradication of the vector bugs. CHEMOTHERAPY The control or treatment of disease by using drugs. CILIATE A group of protozoan having hair-like motile cilia on their cell surface that serve as locomotory organelles. Balantidium coli is the most important ciliate from medical and veterinary poit of view. In ciliates, there are two nuclei, a macro-nucleus and a micronucleus, and a primitive mouth (cytostome). So for about 7000 species have been identifies in this group of which about 2500 are parasitic in in animals and humans. A. G. Arijo
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CLONORCHIS (Chinese liver-fluke) A genus of flukes found in the Far East, where they are common parasites of fisheating mammals, especially cats, as well as humans. There are two intermediate hosts, a snail and a fish. The Chinese liver fluke (C. sinensis), which lives in the bile duct, pancreatic duct, and duodenum, causes the disease clonorchiasis; infestation is caused by eating raw fish. COCCIDIA A group of protozoa parasites which parasitize mammals and birds. The important pathogens include Cryptosporidium, Eimeria, and Isospora, which are mainly parasites of the intestine. The asexual and sexual multiplication of parasite takes place inside host cells. Oocysts are passed in the faeces of the host. One or two hosts may be involved in the life cycle. COCCIDIOSIS An important disease of mammals and birds of worldwide distribution caused by certain protozoa and characterized by infection of the intestines and diarrhoea. Protozoa of the genus Eimeria are the most important cause but certain other coccidia such as isospora may also be responsible. Coccidiosis is transmitted between animals by the ingestion of sporulated oocysts from environment., hence animals kept together become infected easily if only one host becomes infected. The disease may cause depression, A. G. Arijo
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diarrhoea, poor growth, and possibly death. Infection produces a good immunity and disease is usually n only in young animals. In domestic fowls different Eimeria species infect different parts of the intestine. E. tenella causes severe haemorrhages in the caeca, while E. necatrix causes similar lesions in the small intestine. Both these infections can be fatal. E. maxima and E. acervulina are common infections, which are rarely fatal but cause serious impairment of growth and feed conversion efficiency. All Eimeria species are extremely host specific – for instance, none of the species infecting fowls infect turkeys and vice versa. Infection is thus derived only from environmental contamination by other members of the same host species. There is no vaccine widely available and disease is prevented in broiler chickens by the continuous administration of anticoccidial drugs in feed. Coccidiosis is also an important disease in sheep, causing a severe and sometimes fatal diarrhoea in 1-3-mont-old lambs. E. ovnoidalis is the major pathogenic species. There are several other non-pathogenic species that infect lambs and cause high levels of oocysts in feces, which may confuse diagnosis. The diarrhoea in lambs rarely contains blood. In cattle, the disease can occur in slightly older animals at times of stress, as well as in calves. E. zuernii and E. bovis are the major pathogenic species of cattle and buffalo and they cause severe dysentery. In pigs and dogs, coccidiosis is associated with Isospora spp. infections. In rabbits coccidioais is severe and possibly fatal. This species is unusual in that it infects the walls of the bile ducts in the liver. Together with diarrhea, there may be signs jaundice which is due to liver damage. In all species, outbreaks of disease may be treated with specific drugs given in drinking water or feed.
A. G. Arijo
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COCCIDIOSTAT (Anticoccidial) Drugs with activity against coccidian are called coccidiostat. Such drugs are very common in use to control or prevent coccidiosis in livestock and poultry. The sulphonamides were the first effective coccidiostats; the most commonly used compounds are suphaquinoxaline and sulphadimidine. These drugs kill coccidia at the second schizont stage, which is most pathogenic form of the parasite development. Diaveridine is often used in combination with sulphonamides to give a synergistic effect. Both agents act on the same metabolic pathway in coccidia. Ethopabate, a paraaminobenzoic acid antagonist, is used as a coccidiostat, often combined with pyrimethamine or diaveridine. It has no activity against Eimeria tenella. The methyl benzoquate, decoquinate, and clopidol are a group of anticoccidial agents that act against coccidia in epithelial cells. They are poorly absorbed after oral administration. The ionophore group of antimicrobials, including monensin, lasalocid, and salinomycin, have anticoccidial properties. These chemical agents kill the parasites at an early stage in their development. Coccidiostats with various combination os drugs are easily administered in feed or in water. In poultry birds, they should be given continuously until the time of slaughter; the drugs used kill coccidia at an early stage, before the parasites can affect the bird’s growth rate. It is highly important to stop all coccidiostats atleast 15 days before slaughter. This may prevent contamination of carcasses. There are some most recent reports that coccidia can become resistant to certain drugs, therefore; changing the type of coccidiostats at regular intervals prevents outbreaks of coccidiosis due to parasite.
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COENUROSIS (GID) It is a disease caused by coenurus, which is the larval stage of certain tapeworms. The notable infection of coenurosis is caused by Taenia multicep in sheep, goats, The adult parasite is found in small intestine of dogs and foxes. If sheep ingest eggs from pasture contaminated by dog faeces, these eggs hatch to release an embryo, which penetrates the wall of the alimentary tract and is conveyed by the blood to the central nervous system, where it develops over a period of about 6 months to a coenurus measuring up to 5cm in diameter and bearing several hundred scolices for future parasites. The symptoms of gid depend on the site and size of the coenurus. Typically animals with brain coenuri show disorders of gait and stance, often with turning of head towards the affected side, walking in circles towards the same side, and showing a one-sided blindness on the opposite side. Other signs include excitement, in coordination and partial but progressive paralysis with spinal cord involvement. The coenurus may cause a local softening of the skull, which, if detectable, is an aid to diagnosis. The only satisfactory treatment is a difficult surgical removal of the cyst. Since the life cycle of T. multiceps depends on the coenuri being eaten by dogs or foxes, control is best achieved by disposal of all sheep carcasses and remains. Routine treatment of dogs for tapeworms may help reduce the infection. Another form of coenurosis occurs under the skin and in other connective tissues of rabbits and hares. This is caused by T. serialis, whose life-cycle and transmission are similar to T. multiceps. A. G. Arijo
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COENURUS The larval stage of the dog tapeworm Taenia multiceps (Multiceps multiceps). Each coenurus consists of a fluidfilled cyst containing up to 50-60 invaginated tapeworm heads. The cysts develop from eggs eaten by the intermediate host, most commonly sheep, and lodge in the central nervous system, usually the brain, where they cause the disease called gid. If the head of a dead infected sheep is eaten by a dog, the coenurus develops into adult tapeworms. Deworming dogs regularly, burning their faeces, and proper disposal of the sheeps’ heads help prevent gid.
COMMENSALISM An association between host and parasite where none gets harm or benefit. For example, some microorganism living in the gut obtains both food and a suitable habitat but neither harm nor benefit their host. CYSTS A dormant stage produced during the life-cycle of certain protozoan parasites, such as Entamoeba histolytica, that is capable of infecting suitable host when ingested. These protozoans first form the cyst by a process called encyctation, and on reaching the target host, the cyst is rupuured by a process called excystation. A. G. Arijo
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A structure (hydatid cyst) that forms around larvae of Echinococcus tapeworms infecting the tissues of their hosts. Such systs areeither found embedded in various vital organs of body such as lung, liver and spleen or found free in abdominal cavity. CYSTICERCUS The larval stage in the life-cycle of tapeworms of the genus Taenia, which parasitize cats, dogs and humans. It consists of a spherical fluid-filled sac in which the head and neck of a single tapeworm are invaginated. The cysticercus develops from the oncosphere in the intermediate host, usually cattle, sheep, or pigs, where it may cause the disease cysticercosis which gives no symptoms in the intermediate host. In sheep, it is known as Cysticercus ovis and is the larval stage of T. ovis, a parasite of dogs. In cattle it is known as C. bovis, an oval structure up to about 1cm long and the larval stage of T. saginata, the beef tapeworm of humans. C. cellulosae, an elongated cyst slightly smaller than C. bovis, is the larval stage of T. solium of humans and is found in the pigs. When the carcass of the intermediate host is eaten by the final host, each cysticercus develops into an adult tapeworm. CANINE NASAL MITES The canine nasal mite, also known as Pneumonyssoides caninum or Pneumonyssus caninum, has been reported worldwide, including the USA, Canada, Japan, Australia, South Africa, Italy, France, Spain, Norway, Sweden, Finland, Denmark, and Iran.
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Etiology and Epidemiology The canine nasal mite has most commonly been reported in dogs and has also been reported in a silver fox. There does not m to be a breed, age, or sex predilection, although one report suggested that dogs >3 yr old were affected more often and that large-breed dogs had a higher incidence than small-breed dogs. The mites live in the nasal passages and paranasal sinuses. The complete life cycle of P caninum is not known or understood. Transmission is thought to be via direct and indirect contact between dogs. There is no evidence to suggest that P caninum presents a zoonotic risk. Clinical Findings The most common clinical signs associated with nasal mite infestation include epistaxis, sneezing, reverse sneezing, impaired scenting ability, facial pruritus, nasal discharge, head shaking, and stridor. Other reported clinical signs include coughing, restlessness, and collapse. These signs are not specific for nasal mite infection and may indicate many types of upper respiratory disease. Diagnosis Differential diagnoses based on the clinical signs include many upper respiratory diseases such as rhinitis (idiopathic, secondary bacterial, parasitic, or fungal), oronasal neoplasia, dental disease (oronasal fistula), nasal foreign body, or nasopharyngeal disease (foreign body or mass lesions). To exclude concurrent systemic disease, a CBC, serum chemistry profile, and urinalysis should be performed. If epistaxis is present, a one-stage prothrombin time, partial thromboplastin time, and buccal mucosal bleeding time should be considered in addition to a platelet count. COMMUNICABLE DISEASES A. G. Arijo
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A communicable disease such as a cold is a disease that spreads from person to person. Communicable diseases are diseases that you can "catch" from someone or something else. Some people may use the words contagious or infectious when talking about communicable diseases.
D DDT (Dichlorodiphenyltrichloroethane)
An insecticide used to kill and control mainly the insects. It is insoluble in water but very soluble in fats and oils, DDT is rapidly absorbed when taken orally in solution in vegetable oil and can penetrate intact skin when applied in oil or in an emulsion. After absorption it is stored in body fat and persists there for several months. It is excreted in milk, and high concentrations are found in butter made from contaminated milk, DDT does not have a rapid ‘knock-down’ effect, and many insects now show resistance. The chemical is highly Toxic to all species due to damage to the nervous system which leads to death of insect. DDT was used as a pesticide in many countries after world war-II. It breaks down slowly, remaining in the environment for between two and five years. During the 1950s and 1960s, it becameobvious that DDT was affecting whole food web. When applied, DDT is not excreted and concentrates in the fatty tissues of organism. In one research study, the A. G. Arijo
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concentration of of DDT in zooplanktons, the primary consumers in the chain, was only 0.04 parts per million (PPM), its concentration in tissues of top carnivore such as osprey or blad elage was 25 ppm. The bodies of large birds of prey converted the DDT into a substance that made their egg shells very fragile. As a result, very few birds managed to breed and their number fell very quickly. In 1972, DDT was banned and since then, the numbers of the large predatory birds has recovered. However, there are still problems because of the illegal use of DDT. DEMODECTIC MANGE (follicular mange) A form of mange caused by Demodex bovis mites. These mites are transferred from cow to calf while nursing and many considerable damage to hides. Pruritus is absent Lessions consists of follicle papules and nodules, specially over the whiters, neck, back, and flanks. Ulceration, abscesses and fistulae can develop due to follicular rupture or secondary infection. Diagnosisi is made by deep skin scrapings. Bovine demodicosis usually is benign, although the course may extend for many months. Recovery is usually spontaneous. TRichlorfon dips (20%) every other day for three treatments have been reported to be curative. DEMODEX A genus of follicle mites. These mites have a soft elongated body with 8 short legs and piercing sharp mouth-parts. These mites complete whole of their life-cycle on the host A. G. Arijo
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in about 2-4 weeks. They are responsible for the condition known as demodectic mange. There are number of species responsible to cause mange in different animals, for example D. canis is found on dogs, while D. folliculorum, common on humans, D. bovis on cattle, D. ovis on goats and D. equi on horses in various countries of the world. DEPLUMING MITE These are small parasitic mites which burrow into the epidermis as the base of feather shaft and intense irritation and feather pulling in chicken, pheasants, pigeons and geese in spring and summer. Cnemidocoptes gallinae is the only popular species that burrows into the rump, back, head, and neck of the host birds and may develop bald patches, and the skin can become red and inflamed. Apart from discomfort infestation can result in reduced egg infestation can result in reduced egg continual feather regrowth. To control the depluming mites, affected birds should be isolates and treated with ivermectin. DERMACENTOR It refers to genus of some 30 species of hard ticks which parasitize animals in various parts of the world and are commonlu known as wood ticks or dog ticks. D. nitens is of major importance in veterinary medicine. The adults species in this genus are bloodsucking ectoparasites of humans, dogs, cattle, and horses, while the larvae and nymphs are parasites of smaller mammals. Adults can survive for 1-2 ½ years without food and they need three hosts to complete their life cycle. Dermacenter are the chief vectors of Rickettsii riskettsii, the agents or Rocky Mountain spotted A. G. Arijo
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fever. They can transmit the protozoan parasite Babesia, which causes fevers in cattle, horses, and dogs. The bites of these ticks are quite popular for inducing tick paralysis. DERMATITIS Inflamation of skin can be produced by numerous agents, including external irritants, burns, trauma, and infection by parasites, bacteria, virus, and fungi. The mosy common sign is scratching followed by skin lesions that progress from edema and erythrema to pupales, vesicles, oozing, and crusting or scaling. Dermatitis may also cause seco ndary infectopm when it becomes chronic. Before treatment, it is very important to diagnose the cause of dermatitis. DICROCOELIUM A genus of flukes known as lesser liver flukes, commonly found as parasites in the bile ducts of herbivorous mammals. D. dendriticum, the lancet fluke of sheep, is widespread in Europe, Asia, and North America; in the UK it is restricted to a few parts of northwest England, Wales, and Scotland. It is small and elongated with a complex life cycle involving two intermediate hosts. The first is a snail from which the larvae are extruded in balls of mucus. These are eaten by ants of the genus Formica, which is turn are ingested by grazing sheep. The effects on the sheep are similar to those of the liver fluke, Fasciola hepatica, but sheep can withstand a higher infestation before showing pathological signs. Treatment entails administration of a suitable anthelmintic. Control of the snail and removal of ant-hills may assist in prevention.
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DIPYLIDIUM It refers to the genus of tapeworms occurring as parasites in the small intestine of dogs, cats, and occasionally humans. D. caninum, is one of the most important species which parasitize, dog, cat, coyote, wolf, fox, and other animals. It is probably most common tapeworm of dogs, less common in cats; and occasionally infects humans particularly infants. The morphology of D caninum is very simple. The strobila is 15-0 cm long up to 3mm in maximum width, 30-150 rostellar hooks of rose thorn shape in three or four circles, large segments shaped like cucumber ds with spore near middle of each lateral margin. This parasite uses Ctenocephalides canis, C. felis, or Pulex irritans (all fleas) and Trichodectes canis (a biting louse) as intermediate host. The dog and cat act as final host. The parasite reaches its final host when bitten by intermediate host. On reaching in intestine, the hooks on the tapeworm’s head damage the intestinal mucosa and may cause inflammation. The mobile proglottids passing out with the faeces may cause itching around the anus. Treatment entails dosing with an anthelmintic effective against the larvae and adults. Worming should be augmented by bathing the animal with a suitable insecticidal shampoo to destroy any fleas or lice, and insecticidal treatment of the bedding etc. of the dog or cat.
DIROFILARIA A. G. Arijo
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A genus of parasitic nematodes, commonly known as heart-worms. Dirofilaria immitus is the most important species under this genus which has world-wile distribution and infects dog, cat, ferret, fox, sea lion, horse etc. The adult female worm is 27 cm male is 17 cm long. They reside normally in pulmonary arteries and right ventricles without interfering with blood supply. The life-cycle is indirect. Mosquitoes act as intermediate host. With in the mosquito, the vae migrate to the stomach and then to mouth parts during development. When the mosquito feed on final host, the infective larvae called microfilariae are deposited on the skin of the animal and enter through the bite wound. A. single mosquito can deposit 10-12 larvae into hosts skin. In hosts body, 315um long and 6-7 um wide micrifilariae migrate to pulmonary arteries in 100 days after infection. During this time they becobe 1-2 cm long In next 2-3 months, they develop to a mature adult wormand migrate back towards the right ventricle. The new microfilariae are produced 6-7 months after the animal was infected. An adult worm can live 3-5 years. In infected dogs, 15 worms may be n and in cats, is is 3-4 worms in an infected animal. The clinical signs depend on stage of the life-cycle, severity of infection and the host response to infection. Decreased cardiac outputs, nonspecific sign of weight loss, fever, and dyspnea can occur in sever infection. Ascites may develop right sided heart failure from mechanical dysfunction of tricuspid wall. Clinical signs in cats are intermittent coughing and vomiting. There are number of tests such as Knott’s test, thoraci radioghaph, fecal examination, ECG, ELISA etc, but the A. G. Arijo
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easiest way is to detect the microfilariae in wet blood examination of infected dog or cat.The infection may be treated with ivermectin at 50 ug/kg or milbemycin at the preventive dose is effective within 2-3 weeks DIROFILARIASIS It refers to the disease caused by Dirofilaria parasites. It normally affects dogs, and occasionally cats, caused by D. immitis, the canine heartworm. A heavy worm burden may interfere with the blood circulation causing congestion and cirrhosis of the liver. Affected dogs cough, are listless, breathe rapidly, and have a noticeable heart murmur; any sudden exertion results in collapse. DIROFILARIA IMMITIS Dirofilaria immitis is a nematode parasite that causes heartworm disease in dogs, cats and ferrets. Heartworm disease is transmitted by mosquito bites and there are more than 70 species of mosquito that are able to transmit infection; Aedes, Anopheles and Culex are the most common vector species. Heartworm disease has been reported in many countries with temperate climate and is particularly prevalent in the USA, Canada, and southern Europe. The introduction of the PETS travel scheme has increased the concern over Dirofilariasis in many countries. Dirofilaria does have zoonotic potential: infected mosquitos can transmit D. immitis to humans, but the infection does not become patent. The infective larvae instead reach the lungs, become encapsulated, and die causing granulomatous A. G. Arijo
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reactions called "coin lesions" in the process. These are only important because they may be confused with neoplastic metastasis to the lungs on radiography. Life Cycle Dirofilaria immitis adults reach maturity and sexually reproduce in the pulmonary arteries and right ventricle. Adult males are around 15cm in length, and females are around 25cm1. After mating, female worms release larvae known as microfilariae (or L1) into the circulation. When a mosquito takes a blood meal from the infected dog or cat, microfilariae are ingested. Mosquitoes are true intermediate hosts for Dirofilaria immitis, since microfilariae require a period of maturation to L2 then L3 in the vector. The duration of this development depends upon environmental conditions. For example, maturation at 30°C takes around 8 days, but when temperatures are down to 18°C, this takes around one month2. Below 14°C, development is halted and resumes when temperatures rise. In cooler climates, this means that transmission of heartworm disease to new canine or feline hosts can only occur in warmer months. Once matured, L3 in the mosquito migrate to the labium, from which they erupt onto the host's skin as the mosquito feeds. Larvae then migrate into the bite wound and, as most dogs are highly susceptible to heartworm disease, most L3 then establish infection. It takes 2-3 days for L3 to moult to L4, which remain in the subcutaneous tissues for up to two months before becoming young adults (L5) and migrating to the pulmonary arteries. Cats differ from dogs in that they are more resistant to infection with Dirofilaria immitis. A lower percentage of exposed cats develop adult infections, and when this does occur the burden is usually low1. L5 in the pulmonary arteries also have a relatively short (2 year) survival time in cats. Pathogenesis A. G. Arijo
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Heartworm disease primarily affects the cardiopulmonary system and the severity and extent of lesions depends on several factors. These include the number and location of adult worms1, 2, the duration of infection, and the level of activity of the host1. Parasites in the pulmonary arteries cause mechanical irritation, leading to endothelial damage, proliferation of the intima and perivascular cuffing with inflammatory cells. This results in narrowing and occlusion of the vessels which in turn causes pulmonary hypertension. A combination of pulmonary hypertension and inflammatory mediators can lead to an increase in the permeability of pulmonary vessels, giving periarterial oedema and intersitial and alveolar infiltrates. Eventually, irreversible interstitial fibrosis arises. Sequelae to heartworm infection include pulmonary thromboembolism, which can either occur due to the death and metastasis of adult worms, or due to platelet aggregation induced by the parasite. In severe cases, live nematodes can migrate to the right ventricle, right atrium and caudal vena cava. The resulting incompetence of the tricuspid valve, augmented by concurrent pulmonary hypertension, leads to signs of right-sided heart failure. Flow of erythrocytes through the mass of parasites formed can also cause haemolysis and thus haemoglobinaemia. This combination of acute right-sided heart failure and intravascular haemolysis is referred to as "caval syndrome", which in severe cases can also be characterised by thromboembolic events and disseminated intravascular coagulation. Due to the smaller numbers of adult worms, caval syndrome is less common in cats. In cats, heartworm disease generally causes a diffuse pulmonary infiltrate and an eosinophilic pneumonia. Adult worms may die and embolise to the lungs, resulting in severe haemorrhage and oedema of the affected lobe. Immature nematodes have also been known to migrate to sites other than the pulmonary arteries and heart such as A. G. Arijo
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the CNS, eye and subcutaneous tissues. These ectopic infections are far more common in cats than in dogs, suggesting that D. immitis is not well adapted to feline hosts. Dirofilaria immitis infection affects dogs more commonly than cats, and risk is greatest in outdoor animals. Dogs of any age may be affected, but infections are most common in 3 to 8 year old dogs, and medium and large breeds are over-represented1, 3. In cats, there are no breed or age predispositions, but males are more frequently affected3. Ferrets may also contract dirofilariasis; there are no age or sex predilections. Clinical Signs In dogs, historical findings at the time of presentation can vary. Some animals are asymptomatic, or cough only occasionally. In countries where heartworm is endemic, animals may be routinely tested for dirofilariasis six months after the end of the high-risk season3. Therefore, positive laboratory testing may be the first indication of disease1. More obvious signs may be n depending on the severity of disease. Generally, the onset of heartworm disease is insidious, and clinical signs are related either to a high parasite burden, or to an allergic response to the parasite. Affected dogs most often show coughing, and dyspnoea/tachypnoea, exercise intolerance, loss of condition and syncope may also be noted. In severe cases the pulmonary vessels may rupture, leading to haemoptysis or epistaxis. There is a tendency for signs to only manifest during exercise, and so patients with a sedentary lifestyle may never show overt disease. Right-sided congestive heart failure may ensue when worm burden is high, and signs can include jugular distension, ascites, marked exercise intolerance and hepatomegaly. A systolic murmur is sometimes audible on cardiac auscultation.
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DOURINE A chronic veneral disease of horses that is transmitted during sexual mating (coitus) and caused by a flagellated protozoan Trypanosom equiperdum, The disease is recognized in various regions of Asia, Africa, Middle East, and South America. The signs of the disease develop in week or months after infection. Some signs include mucopurulent discharge from urethra and vagina of male and female infected horse. Swelling of the genitalia, slight fever, plaques of 2-10 cm in diameter appear on the flanks as if coins have been inserted into skin. The infected horse becomes emaciated gradually and finally muscular paralysis appears, which is usually fatal unless the inefection is treated. The parasites can be found in smears made from genital membranes, the skin swellings, or blood. Several drugs are effective as treatment and the disease has been eradicated from many areas by the detection of carriers using blood tests, and by the control of mating. DRACUNCULUS It refers to a genus of nematodes parasites. The genus is important because it includes species that parasitize humans and animals. D medenensis is mainly found in humans and D. insignis is found in raccoons and some times in dogs. However, D medenensis is very dangerous and causes great sufferings even today. A. G. Arijo
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D medinensis is is one of the largest nematode known. Adult female have been recorded up to 800 mm long, where male can hardly reach 40mm length. This species of parasite is ovo-viviparous. When the parasite is gravid, the thousands of embryos in the uteri cause a high internal pressure. At this stage the female migrates to skin of the host. Usually legs or feet are affected. The presence of parasite produce a blister in the skin which eventually ruptures , giving an exit to young worms, which come out on the surface of the skin. If an infected person goes to water for any reason, the juvenile worms enter into water wher theay can survive for four to seven days. These larvae are eaten by cyclopes in which they take 12-14 days to become infective larvae. The definitive host is infected by swallowing infected Cyclopes with drinking water.The released juvenile penetrate the duodenium, cross the abdominal mesenteries, pierce the abdominal muscle, and enter the subcutaneous connective tisues, where they migrate to axillary and inguinal region. The third molt occurs about 20 days after infection and final one at about 43 days. The males die between the third and seventh month, whereas the femle will migrate to the skin to continue the life-cycle. DRACUNCULIASIS It refers to the disease caused by parasites belonging to genus dracunculis. The female worm may produce allergic reactions around the skin. The reaction results in an itchy, red pupale that rapidly transforms into a blister. During this nausea, diarrhea, dizziness and edema are general conditions. The blister formed by female parasite may become abscessed, but this heals if secondary bacterial infection does not occur. Worms that fails to reach the skin causes complications in deeper tissue of the body. Most serious symptoms such as paraplegia results from a worm in central nervous system. Adult worms have also been reported in heart and urogenital system. A. G. Arijo
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There are quiet a few ways to treat and handle the situation, but the most effective may is the careful, slow extraction of parasite, which usually takes three weeks. Administration of miridazole or benzimidazole compounds may be useful. Supply of safe drinking water and health education are said to play role in eradication of infection. DRACUNCULIS MEDINENSIS Guinea-worm disease is caused by the parasitic worm Dracunculus medinensis or "Guinea-worm". This worm is the largest of the tissue parasite affecting humans. The adult female, which carries about 3 million embryos, can measure 600 to 800 mm in length and 2 mm in diameter. The parasite migrates through the victim's subcutaneous tissues causing severe pain especially when it occurs in the joints. The worm eventually emerges (from the feet in most of the cases), causing an intensely painful oedema, a blister and an ulcer accompanied by fever, nausea and vomiting. Infected persons try to relieve the burning sensation by immersing the infected part of their body in local water sources, usually ponds water. This also induces a contraction of the female worm at the base of the ulcer causing the sudden expulsion of hundreds of thousands of first stage larvae into the water. They move actively in the water, where they can live for a few days. More details. For further development, these larvae need to be ingested by suitable species of voracious predatory crustacean, Cyclops or water fleas which measure 1–2 mm and widely abundant worldwide. In the cyclops, larvae develop to infective third-stage in 14 days at 26°C.
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When a person drinks contaminated water from ponds or shallow open wells, thecyclops is dissolved by the gastric acid of the stomach and the larvae are released and migrate through the intestinal wall. After 100 days, the male and female meet and mate. The male becomes encapsulated and dies in the tissues while the female moves down the muscle planes. After about one year of the infection, the female worm emerges usually from the feet releasing thousands of larvae thus repeating the life cycle. No drug is available to prevent or heal this parasitic disease exclusively associated with drinking contaminated water. Dracunculiasis is, however, relatively easy to eliminate and eventually eradicate. Guinea-worm disease is rarely fatal. Frequently, however, the patient remains sick for several months, mainly because: The emergence of the worm, sometimes several, is accompanied by painful oedema, intense generalised pruritus, blistering and an ulceration of the area from which the worm emerges. The migration and emergence of the worms occur in sensitive parts of the body, sometimes the articular spaces can lead to permanent disability. Ulcers caused by the emergence of the worm invariably develop secondary bacterial infections which exacerbate inflammation and pain resulting in temporary disability ranging from a few weeks to a few months. Accidental rupture of the worm in the tissue spaces can result in serious allergic reactions.
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DRENCHING It refers to the oral administration of a liquid medication. The neck of the drenching bottle should be placed towards the back of the tongue, to prevent spillage and to stimulate swallowing. Large volumes of liquid should be delivered in several stages so the animals can swallow each mouthful, otherwise there is a risk that liquid may be aspirated into the lungs. The bottle should be shatter-proof (e.g. tough plastic), not glass. Routine drenching with anthelmintics is often performed with a drenching gun. This delivers a preset dose of the drug with each squeeze of the trigger, enabling rapid dosing of large numbers of animals. However, care must be taken to ensure that the barrel or nozzle does not damage the animal’s throat when inserted. Hence the animals must be properly restrained particularly its head. DWARF TAPEWORM Also called Hymenolepis nana, Dwarf Tapeworm is a tiny intestinal tapeworm, is the most common human cestode; infection is treated with praziquantel. H. nana is only 15 to 40 mm long. It requires only one host but can also cycle through two. Its larvae migrate only within the gut wall, and its life span is relatively short (4 to 6 wk). H. nana is more frequent in populations living in conditions of poverty and poor hygiene, particularly when fleas are present. A. G. Arijo
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H. nana has 3 modes of infection: Indirect 2-host cycle: Rodents are the primary definitive hosts, and grain beetles, fleas, or other insects feed on contaminated rodent droppings as intermediate hosts; humans can become infected by ingesting parasitized insects. Life Cycle Human-to-human oral-anal cycle: Eggs are passed from one human to another or recycle externally in a single host. Internal autoinfection: Eggs hatch within the gut and initiate a 2nd generation without ever exiting the host. Symptoms: Autoinfection can result in massive numbers of worms, which can cause nausea, vomiting, diarrhea, abdominal pain, weight loss, and nonspecific systemic symptoms. Infections are often asymptomatic, but heavy infections may cause crampy abdominal pain, diarrhea, anorexia, weight loss and pruritis ani. Diagnosis: Diagnosis is made by finding eggs in stool samples. Treatment: Praziquantel,Alternatively, nitazoxanide.
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E EAR MANGE A form of mange caused by Otodectes mites which mostly infest cats, dogs, foxes and ferrets. O cynotis is a very common species which is found in the ears, although other ppartes of the head may be infested. Thousands of these mites swarming in the ear of host can cause desparate distress, with scabby, flowing ears fit-like behaviour.The problem is treated and handelled as it is done in case of other mange forms. ETIOLOGY The study or science of the causes of disease is called etiology. EAST COAST FEVER Also known as Bovine theileriosis east cost fever is an acute and frequently fatal form of theileriosis in cattle. It is caused by the Theileria parva which is transmitted by the brown ear tick, Rhipicephalus appendiculatus. The fever is characterized by enlarged lymph nodes, which become apparent some 10-15 days after infected ticks feed on the host. The first node to become enlarged is the parotid lymph A. G. Arijo
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node below the ear, which is at the feeding site of the tick. In old cases the animal becomes severely depressed and avoids or completely stops eating. There may be diarrhoea and discharges from the nose and eyes. Breathing becomes laboured due to oedema of the lungs, from which death may occur in 1-2 weeks after infection. The cattle if recovers, may become carriers of the infection. A good immunity develops in recovered animals. A frequesnt and regular use of acaricides may help control the ticks. However, for East Cost Fever, a specific and effective drug of choice is parvaquone ECHINOCOCCUS It refers to the genus of smalest tape-worms in the family Taeniidae. The most important species are Echinoccus granulosis, and E multilocularis. Echinococcus granulosis is a tape-worm found in the small intestine of the canid definitive host. The parasite body consists of 2-5 segments with a 2-6mm long strobila. The first segment is immature, the second one is mature and the third one is gravid filled with eggs. The eggs of this parasite are ingested by the intermediate host, wild and domestic herbivores, e.g. sheep, goat, cattle and buffalo. Man can also serve as an intermediate host. After hatching in the intestine of the intermediate host, the oncospheres invade the circulatory system and lodge in various organs. The liver and lungs are the main choice, where they develop into a large, thickwalled, uniloccular hydatid cyst that bud protoscolices endogeneously. Hydatids have been rarely reported in CNS of domestic animals and rare in man, in which if produced may give symptoms similar to brain tumor. The Echinococcus multilocularis occurs in fox definitive host, while rodents act as intermediate host. This parasite has been rarely found in the brain of man, in which the invasive, thin-walled multilocular hydatid cysts do not produce scolices. A. G. Arijo
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The adult parasites in genus echinoccus are not pathogenic, however, the effect of hydatid may become apparent for many years after infection because of its usual slow growth. Up to 20 years, may elapse between infection and overt pathogenesis. If infection occurs early in life, the parasite may be almost as old as its host. The severity of pathological condition depends on the site and size of cyst. The diagnosis of hydatid cyst is possible by X-radiography or ultrasonography. Several immunodiagnostic techniques are also available. The infection is treated through surgical removal o fthe cyst, however, for inoperable cyst, albendazole is recommended. ECHINOCOCCUS GRANULOSUS Human echinococcosis is a parasitic disease caused by tapeworms of the genusEchinococcus. The 2 most important forms of the disease in humans are cystic echinococcosis (hydatidosis) and alveolar echinococcosis. Humans are infected through ingestion of parasite eggs in contaminated food, water or soil, or through direct contact with animal hosts. Echinococcosis is often expensive and complicated to treat, and may require extensive surgery and/or prolonged drug therapy. Prevention programmes involve deworming of dogs, improved slaughterhouse hygiene, and public education campaigns; vaccination of lambs is currently being evaluated as an additional intervention.
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More than 1 million people are affected with echinococcosis at any one time. WHO is working towards the validation of effective cystic echinococcosis control strategies by 2018. Human echinococcosis is a zoonotic disease (a disease that is transmitted to humans from animals) that is caused by parasites, namely tapeworms of the genusEchinococcus. Echinococcosis occurs in 4 forms: Cystic echinococcosis, also known as hydatid disease or hydatidosis, caused by infection with Echinococcus granulosus; alveolar echinococcosis, caused by infection with E. multilocularis; polycystic echinococcosis, caused by infection with E. vogeli; unicystic echinococcosis, caused by infection with E. oligarthrus. The two most important forms, which are of medical and public health relevance in humans, are cystic echinococcosis and alveolar echinococcosis. Transmission A number of herbivorous and omnivorous animals act as intermediate hosts of Echinococcus. This means they get infected by ingesting the parasite eggs in the contaminated ground and develop parasitic larval stages in their viscera. Carnivores are definitive hosts for the parasite, and are infected through the consumption of viscera of intermediate hosts that harbour the parasite and also through scavenging infected carcases. Humans are accidental intermediate hosts and are not able to transmit the disease. A. G. Arijo
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Cystic echinococcosis is principally maintained in a dog– sheep–dog cycle, yet several other domestic animals may be involved including goats, swine, horses, cattle, camels and yaks. Alveolar echinococcosis usually occurs in a wildlife cycle between foxes, other carnivores and small mammals (mostly rodents). Domesticated dogs and cats can also be infected.
Signs and symptoms Human infection with E. granulosus leads to the development of one or more hydatids located mainly in the liver and lungs, and less frequently in the bones, kidneys, spleen, muscles, central nervous system, and eyes. The asymptomatic incubation period of the disease can last many years until hydatid cysts grow to an extent that triggers clinical signs. Non-specific signs include anorexia, weight loss and weakness. Other signs depend on the location of the hydatid(s) and the pressure exerted on the surrounding tissues. Abdominal pain, nausea and vomiting are commonly n when hydatids occur in the liver. If the lung is affected, clinical signs include chronic cough, chest pain and shortness of breath. Alveolar echinococcosis is characterized by an asymptomatic incubation period of 5–15 years and the slow development of a primary tumour-like lesion which is usually located in the liver. Clinical signs include weight loss, abdominal pain, general malaise and signs of hepatic failure. Larval metastases may spread either to organs adjacent to the liver (e.g. the spleen) or distant locations (lungs, brain) following dissemination of the parasite via the blood and A. G. Arijo
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lymphatic system. If left untreated, alveolar echinococcosis is progressive and fatal. Distribution Cystic echinococcosis is globally distributed and found in every continent except Antarctica. Alveolar echinococcosis is confined to the northern hemisphere, in particular to regions of China, the Russian Federation and countries in continental Europe and North America. In endemic regions, human incidence rates for cystic echinococcosis can reach greater than 50 per 100 000 person-years, and prevalence levels as high as 5–10% may occur in parts of Argentina, Peru, east Africa, central Asia, and China. In livestock, the prevalence of cystic echinococcosis found in slaughterhouses in hyperendemic areas of South America varies from 20–95% of slaughtered animals. The highest prevalence is found in rural areas where older animals are slaughtered. Depending on the infected species involved, livestock production losses attributable to cystic echinococcosis stem from liver condemnation, reduction in carcass weight, decrease in hide value, decrease of milk production, and reduced fertility. Diagnosis Ultrasonography is the imaging technique of choice for the diagnosis of both cystic echinococcosis and alveolar echinococcosis. This technique is usually complemented or validated by computed tomography (CT) and/or magnetic resonance imaging (MRI) scans. Sometimes, cysts can be incidentally discovered by radiography. Specific antibodies are detected by different serological tests and can support diagnosis. Biopsies and ultrasound-guided punctures may also be performed for differential diagnosis of cysts from tumours and abscesses. A. G. Arijo
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Treatment Both cystic echinococcosis and alveolar echinococcosis are often expensive and complicated to treat, sometimes requiring extensive surgery and/or prolonged drug therapy. Four options exist for the treatment of cystic echinococcosis: percutaneous treatment of the hydatid cysts with the PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique; surgery; anti-infective drug treatment; ‘watch and wait’. The choice must primarily be based on the ultrasound images of the cyst, following a stage-specific approach, and also on the medical infrastructure and human resources available. For alveolar echinococcosis, early diagnosis and radical (tumour-like) surgery followed by anti-infective prophylaxis with albendazole remain the key elements. If the lesion is confined, radical surgery offers cure. Unfortunately, in many patients the disease is diagnosed at an advanced stage, and palliative surgery, if carried out without or with incomplete anti-infective treatment, frequently results in relapses. Health and economic burden Both cystic echinococcosis and alveolar echinococcosis represent a substantial disease burden. Worldwide, there may be in excess of one million people living with these diseases at any one time. Many of these people will be experiencing severe clinical syndromes which are lifethreatening if left untreated. Even with treatment, people often face reduced quality of life. For cystic echinococcosis, there is an average 2.2% postoperative death rate for surgical patients and about A. G. Arijo
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6.5% of cases relapsing after intervention that require prolonged recovery time. Present estimates suggest that cystic echinococcosis results in the loss of at least one million DALYs1 annually and possibly up to three million. Annual costs associated with cystic echinococcosis are estimated to be 3 billion US dollars for treating cases and losses to the livestock industry. Alveolar echinococcosis results in the loss of about 650 000 DALYs annually, with most of the disease burden concentrated in western China. Surveillance, prevention and control Surveillance for cystic echinococcosis in animals is difficult because the infection is asymptomatic in livestock and dogs. Surveillance is also not recognized or prioritized by communities or local veterinary services. Cystic echinococcosis is a preventable disease as it involves domestic animal species as definitive and intermediate hosts. Periodic deworming of dogs, improved hygiene in the slaughtering of livestock (including proper destruction of infected offal), and public education campaigns have been found to lower and, in high income countries, prevent transmission and alleviate the burden of human disease. Vaccination of sheep with an E. granulosus recombinant antigen (EG95) offers encouraging prospects for prevention and control. Small-scale EG95 vaccine trials in sheep indicate high efficacy and safety with vaccinated lambs not becoming infected with E. granulosus. A programme combining vaccination of lambs, deworming of dogs and culling of older sheep could lead to elimination of cystic echinococcosis disease in humans in less than 10 years.
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Alveolar echinococcosis prevention and control is more complex as the cycle involves wild animal species as both definitive and intermediate hosts. Regular deworming of domestic carnivores that have access to wild rodents should help to reduce the risk of infection in humans. Culling of foxes and unowned free-roaming dogs is applicable but appears to be highly inefficient. Deworming of wild and stray definitive hosts with anthelminthic baits resulted in significant reductions in alveolar echinococcosis prevalence in European and Japanese studies. Sustainability and cost–benefit effectiveness of such campaigns are however controversial. ECTOPARASITE A parasite that lives on the outside of the host body is called ecto-parasite. Some ecto-parasites can not live away from the host body, such are called permenant or obligatory ectoparasites e.g. lice. Those which just visit their host body, take their meal and go away are called visiting or temporary ecto-parasites, e.g. mosquito and sand flies. ECTO-PARASTICIDES It refers to the drugs or chemicals which are used to kill ectoparasites. Some very common ectoparasiticides include organochlorines, organophosphorus compound, carbamates, pyrethroids, derris, sulphur compounds, and ivermectin. They can be applied in different ways, for example, sprays, washes, dips, powders, pour-ons, spotons, or impregnated collars, or injected parenterally.
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ECZEMA Eczema, or dermatitis is a group of skin conditions which can affect all age groups of animal and men. The severity of the disease can vary. In mild forms the skin is dry, hot and itchy, whilst in more severe forms the skin can become broken, raw and bleeding. Although it can sometimes look unpleasant, eczema is not contagious. With treatment the inflammation of eczema can be reduced, though the skin will always be sensitive to flare-ups and need extra care. The causes of eczema are many and varied, and depend on the particular type of eczema. There are several different types of eczema, many of which look similar but have very different causes and treatments. The first step in effective treatment of eczema is a correct diagnosis. It is very important to a general practitioner in the first instance, who may make a referral to a specialist dermatologist for further diagnosis and treatment. EIMERIA Eimeria are often referred to as the "coccidia.". The genus contain a large number of species that infect a variety of animals throughout the world. The diseases caused by these parasites are referred to collectively as coccidiosis, and they vary A. G. Arijo
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tremendously in virulence. Some species cause diseases that result in mild symptoms that might go unnoticed (i.e., mild diarrhea) and eventually disappear, while other species cause highly virulent infections that are rapidly fatal. The life cycles of the parasite need only single host. A host is infected when it ingests oocysts that have been passed in the feces of another host. The oocyst excysts in the host's small intestine, and the sporozoites contained within the oocyst are liberated. The sporozoites penetrate the cells of the host's small intestine and reproduce asexually. Each generation of asexual reproduction produces multiple merozoites; the merozoites are liberated from the cell and infect new cells. It is this stage of the infection that can result in destruction of massive numbers of cells in the host's small intestine and, ultimately, lead to the host's death. Some of the merozoites that enter the host's cells transform into gametocytes. The gametocytes transform into gametes, the gametes fuse, and the resulting zygote begins to develop into an oocyst. The developing oocyst escapes from the host's cell, and it is passed in the host's feces. Typically, when the oocyst is passed in the feces, it is not infective because it does not contain sporozoites; this is an unsporulated oocyst. After several days (or weeks, depending on the species) outside of the host's body, the oocyst completes development and sporozoites are found within; this is a sporulated oocyst, and it is infective to the next host. Diagnosis of the infection is based on finding oocysts in the host's feces. While it is possible to identify an unsporulated oocyst as a coccidian oocyst, it is virtually impossible to identify the parasite that produced the oocyst until the oocyst is sporulated. Asexual multiplication of the parasite in the cells of the host's small intestine is self limiting (although in some species the parasite actually kills the host before asexual reproduction stops). That is, after several generations of asexual multiplication, the parasite simply stops dividing, the A. G. Arijo
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host stops passing oocysts, and the host is effectively cured of the infection. ENTAMOEBA A genus of amoeban protozoa that are parasitic in the digestive tract; most of them are non-pathogenic. The normal feeding stage is quadricnucleated and varies in shape as the organism moves by extending pseudopodia. Entamoeba also form nucleated rigid-walled cysts that are passed in faeces. The only species causing disease in mammals is Entamoeba histolytica, which causes amoebic dysentery in humans and occasionally in other primates and dogs but rarely in other species. It may be distinguished from other non-pathogenic species by the number of nuclei in the cyst, and by its habit of engulfing red blood cells. ENTAMOEBA HISTOLYTICA E. histolytica is a parasite that lives in the human intestine and cause amoebic dysentery. Complications arise when this parasite invades the intestinal lining and reproduces there. This parasite was first discovered by D.F. Losch in Rusia E. histolytica is the third most common cause of parasitic death in the world. Close to 500 million people are infected at any one time, with up to 100,000 deaths per year. The parasite has many stages, such A. G. Arijo
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as trophozoite, precyst, cyst, metacyst, and metacystic trophozoite. Trophozoite, which is feeding stage is 20-30um. It lives and multiplies within musoca of large intestine, where it feeds on starches and musous secretions. The amoeba induce ulcer into the intestinal wall, eventually reaching the submucosa and underlying blood vessels. From there may travel with blood to other sites of body, such as liver and lungs etc. The trophozoite produce cysts which is sent out of host body through feces. The cyst of E histolytica can remain viable and infective in a moist and cool environment for at least 12 days and in water for 30 days. The cyst are easily and rapidly killed by putrefaction, desiccasion, and temperatures below 5C° and above 40C°. When such cysts are sallowed, the cyst passes through the stomach unharmed and shows no activity while in acidic environment. When it reaches in small intestine, the metacyst begins to move with in The parasite may live in the lumen of large intestine as a commensal organism or invade the intestinal mucosa and produce mild to severe ulcerative hemorrhagic colitis. In acute disease, fulminating dysentery may develop, which may be fatal, progress to chronicity, or resolve spontaneously. In chronic condition, there may be weight loss, anorexia, tenesums, and chronic diarrhea or dysentery, which may be continuous or intermittent. E. histolytica may some time infect perianal skin, genitalia, liver, brain, lungs, kidneys and other organs. EPIDEMIOLOGY It is a study about spread of disease in animals and human beings.
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EQUINE BABESIOSIS A disease of horses caused by the protozoan parasite B. equi. B. equi is smaller (2-3 μm) long) and occasionally forms linked groups of four organisms in a Maltese cross shape. B equi widely distributed throughout the world, generally in tropical and subtropical areas. It is transmitted by ticks of the genera Dermacentor, Hyalomma, and others. The parasite multiples in the host’s red blood cells causing fever, anaemia, jaundice, and sometimes haemglobinuria. The disease can be fatal. Diagnosis is confirmed by the finding of parasites in stained blood smears during the early stages of disease. EQUINE FILARIASIS A disease of horses caused by filarial nematode called Setaria equina, which is found in the peritoneal cavity. The larvae are transmitted by mosquitoes vetor and other biting flies. The disease, is debilitating rather than serious, causing anaemia and general malaise. However, movement of the nematodes to other sites can cause conjunctivitis and oedematous swellings. Affected animals are normally treated with diethylcarbamazine. ETIOLOGY
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It refers to knowledge concerned with causes and origins of diseases EYEWORM It refers to the parasitic nematodes that occur on or in the eye. Worms of the genus Thelazia infect dogs, ruminants, and occasionally humans. They normally remain in the inner corner of the eye, preferring the conjunctival sac and nasolacrimal duct, but can sometimes be n creeping over the eyeball surface. The worm’s rough cuticle abrades the surface of the eyeball and the irritation stimulates tear flow and dilatation of the blood vessels. Scar tissue may develop leading to blindness in severe cases. Secondary infections may arise, with consequent keratitis, conjunctivitis, ophthalmia, and a purulent discharge, which may cause the eyelids to gum together. The intermediate hosts are flies (Musca spp.), which often collect around the eye. Treatment involves local application of diethylcarbamazine or dosing with levamisole or tetramisole. This should be followed by application of an antibiotic eye ointment. In monkeys and humans the filarial worm Loa loa wanders beneath the skin causing an itching sensation. It can also migrate to the eye. The motile embryos are present in the blood and the intermediate hosts are certain bitting flies (mango flies).
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F FACE FLY The face fly, Musca autumnalis, is a robust fly that superficially resembles the house fly. It is a nonbiting fly that feeds on animal secretions, nectar, and dung liquids. Adult female face flies typically cluster around the animals’ eyes, mouth, and muzzle, causing extreme annoyance. Their activity around the animals’ eyes allows face flies to serve as vectors of eye diseases and parasites such as pinkeye and Thelazia eyeworms. They are also facultative blood feeders, meaning that they gather around wounds caused by mechanical damage or biting fly activity to feed on blood and other exudates. Male face flies feed only on nectar and dung. They spend much of their time resting on branches and fences and attempting to catch and copulate with female flies as they move about. Females lay their eggs on very fresh droppings on pasture, and development from egg to adult is completed in about 2 to 3 weeks, depending on temperature. FACIAL ECZEMA It refers to a type of hepatogenous photosensitization that occurs in sheep and cattle. It affects animal grazing rapidly growing rye-grass A. G. Arijo
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pastures when conditions of temperature and moisture facilitate the rapid multiplication of the fungus Pithomyces chartarum. The spores of this fungus contain the mycotoxin sporidesmin, which causes necrosis of liver cells. The necrotic areas are infiltrated by new cells and there is fibrosis and proliferation of disorganized bile ducts. The excretion of bilirubin and phylloerythrin is impeded and because the latter is a photodynamic agent the animals become sensitive to sunlight. Their face and ears swell and become scabby and necrotic, resembling eczema. Some affected animals die; others recover partially but liver damage persists and growth is poor. FASCIOLA A genus of trematode prasites. Liver fluke, (Fasciola hepatica) which is a common example in this genus, is found worldwide in the bile ducts of most herbivores and occasionally in man. It causes fascioliasis in sheep, goat and cattle. F. gigantica is another species in this genus, and it is a larger species found in sheep and cattle in tropical Africa and Asia. FASCIOLIASIS It refers to a disease caused by Fasciola flukes. The most widespread species is the liver fluke F. hepatica, which infests principally sheep, goats, and cattle, although many other mammalian species, including humans, are susceptible. Part of the life cycle is spent in an intermediate host, a snail of the genus Lymnaea, from which cercariae emerge to form cysts (metacercariae) attached to vegetation when a final host ingests metacercariae, the young parasites emerge from the cysts in the intestine, penetrate the peritoneal cavity, and enter the liver, where they cause tissue destruction by feeding on the liver parenchyma. This phase of parasitism lasts 6-7 weeks, after which the flukes A. G. Arijo
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enter the bile ducts, reach maturity, and lay eggs, which appear in the faeces. The spread of disease depends much on weather conditions. Acute fascioliasis is the rarer form of the disease and is largely restricted to sheep. It results from simultaneous liver infestation by large numbers of young flukes following the release of many cercariae from welldeveloped of their maximum abundance, usually mid- to late summer. Acute fascioliasis tends to follow snail numbers and rates of snail infestation are high. Owing to the time required for the parasite to develop in the snail, acute fascioliasis is usually evident in sheep late in the year, causing sudden death. Blood may be present at the mouth and anus of the carcass. The condition is sometimes complicated by the toxaemia due to bacterial infection known as black disease. Liver destruction and the presence of the young parasites are evident at post mortem. Chronic fascioliasis occurs as a result of the gradual acquisition of parasites over a period. It is the commoner form, particularly in mammals other than sheep. The primary lesion is a chronic usually progressive fibrosis of the liver. The bile ducts frequently show hyperplasia and, later, loss of their epithelium; their walls are thickened and may eventually become calcified. Affected animals also tend to show progressive anaemia, low plasma albumin, submandibular oedema (‘bottle jaw’), depression, and weight loss. These changes are less common in cattle than sheep. In adult dairy cows, reduction in milk yield may occur. Clinical signs appear only when sufficient parasites have been acquired; hence the chronic form is much less clearly seasonal than the acute form. Diagnosis of fascioliasis is confirmed by demonstrating F. hepatica eggs in the faeces. In principle, prevention can be achieved by draining land or applying mollusicides to remove snails. Study of meteorological records enables forecasting of heavy A. G. Arijo
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cercarial release so that in bad years the worst affected pastures can be avoided. Anthelmintics give clinical benefit and also reduce egg output so restricting snail infestation. In Africa and India F. gigantica is the predominant liver fluke. The life the predominant liver fluke. The life cycle and pathogenicity are generally similar to F. hepatica, with various species of Lymnaea serving as intermediate host. FASCIOLA HEPATICA The most common trematode parasite in genus Fasciol. It is large leaf shaped parasites of mammal, mainly herbivores. Geographical Distribution With world distribution
wide
-Domestic livestock: sheep, cattle -Other mammals including humans. Intermediate host -Fossaria modicella or Stagncola bulimoides (water snails) Morphology Fasciola hepatica is one of the largest flukes in the world. It is 30 mm in length and 13 mm wideLeaf shaped. It has an oral sucker and an acetabulum. The testes are highly branched and lie behind the branched ovaries. Vitellaria lies on the outside the testes filling most of the lateral body. The eggs are operculated and are 130-150 microns by 63-90 microns. Life cycle A. G. Arijo
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Adult flukes feed on the lining of the bile ducts. They pass their eggs out of the bile ducts. The eggs pass through the intestine and out into the feces. If the eggs reach water they will finish their development into miracidia and hatch out. Miracidia must find a snail host in 24 hours or they will die. If they find a snail host the miracidia will penetrate the soft tissue of the snail and produce a mother sporocyst. A mother sporocyst produces multiple daughter rediae. These will produce more daughter rediae that develop into cercariae. The cercariae emerge from the snail. They have a club shaped tail that allows them to swim and find the nearest object to penetrate. Once the cercariae penetrate an object they drop their tails and encyst as a metacercariae. When a host ingests the metacercariae it will go to the small intestines, excyst, penetrate the intestinal wall and live there for 2 months. After two months the fluke will migrate to the bile ducts, mature and produce eggs. Pathogenesis The juveniles cause much damage to the liver as a result of migration through the liver. Anemia can result from heavy infections. Worms in the bile ducts cause inflammation and edema which stimulates the production of fibrous tissue in the ducts. Bile ducts become thickened and less responsive to the needs of the liver. Back up of bile causes jaundice and cirrhosis. Migrating juveniles can reach the eye, brain, skin, and lungs causing an abscess to develop. Diagnosis and Treatment Find eggs in feces, ELISA tests are available Rafoxanide is an effective drug against this worm. Control Control reservoir host populations. Stay away from raw liver consumption. Avoid eating watercress from pastures. Control snail population. A. G. Arijo
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FILARIA It refers to group of threadlike nematodes. As adult, they are parasites in the blood or lymphatic systems, connective tissue, body cavities, eye sockets, or nasal cavities of animals and human beings. Some important species such as Brugia malayia, Dirofilaria immitus, and Onchocerca volvulus. FILARIASIS Group of diseases caused by filarial nematodes, for example Dirofilariasis, and Stephanofilariasis. FLAGELLATE Any of the protozoans that bears one or more flagella. For example Trypanosoma cruzi, Trichomonas foetus, Giardia lamblia. FLAGELLUM A thread-like structure found in uni-cellular organisms. Flagella are responsible for the movement of the organisms to which they are attached. FLEA It is a wingless insect belonging to the order Siphonaptera. Fleas are ectoparasite of mammals and birds, living in the coat or (rarely) just beneath the skin and feeding on the blood of their host. Their mouthparts are specialized for biting and A. G. Arijo
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sucking; the body is laterally compressed to facilitate movement over the host’s body, and the limbs are adapted for clinging and for jumping from host to host. The eggs hatch into whitish wormlike larvae, which feed on organic matter for example in the host’s nest or bedding. After two moults the larva spins a cocoon undergoes metamorphosis into the adult. Many species infest more than one host. The dog flea, Ctenocephalides canis, can also occur on cats and humans. It causes severe irritation and, if infestation is severe, anaemia in young animals. The host’s immune system may become sensitized to flea bites resulting in a form of eczema. Similar conditions are caused in their respective hosts by the cat flea, C. felis, and the human flea, Pulex irritans, and all three species may transmit the tapeworm, Dipylidium caninum, initially ingesting tapeworm eggs in the larval flea stage. The rate fleas, Nosopsyllus fasciatus and Xenopsylla cheopis, and the European rabbit humans, and the European rabbit flea, Spilopsyllus cuniculi, transmits myxomatosis to rabbits. The chickens flea or ‘stick-tight’, Echidnophaga gallinacea, is common in poultry, especially in tropical regions, and can cause skin ulcers. Jiggers, or chigoes are fleas of the tropical genus Tunga, found in America and Africa. They can infest humans and all domestic livestock. In all cases, treatment entails dressing the animal’s coat with flea powder or aerosol spray containing a suitable insecticide. Precautions should be taken to prevent inhalation or contact with the eyes. Pets can also be treated with an insecticidal shampoo or fitted with a flea collar. To prevent reinfestation, housing and/or bedding should be thoroughly cleaned and treated with insecticide. Ideally old bedding materials should be burnt. FLUKES A. G. Arijo
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It refers to parasitic trematodes commonly called flatworms They have short unsegmented flattened bodies, covered by a protective cuticle, and bear hooks or suckers for attachment to their host. There are two main groups: the Monogenea, which are mostly parasites of the skin and gills of fish, and the Digenea. Flukes parasitize the intestine, biliary system, vascular system, and urogenital tract of vertebrates, and include several important pathogens of domestic animals and humans, such as, Fasciola hepatica and Schistosome parasites. Typically, digenetic flukes are hermaphrodite. Their eggs develop and hatch after leaving the host to produce a ciliated larva, the miracidium. This finds and penetrates an intermediate host, usually a gastropods mollusc, before developing further to form a sporocysts. In turn this gives rise to a further larval stage, the redia. The final larval stage, the cercaria, leaves the mollusc to infect, via various routes, the final host, where it grows into the mature fluke. FLY An insect belonging to the order Diptera. They are relatively small and possess two pairs of wings. The first pair is used in flying and the second one clled halters is used in balancing the body during flight. Flies have variety of mouth parts. Some have piercing and sucking mouthparts for feeding on sucking mouthparts for feeding on plant fluids, decaying organic matter, or blood. Flies have complete metamorphosis, i.e Adult-egg-larva-pupa. The eggs hatch into larvae called maggots; eventually a pupa forms in a puparium, in which it develops into an adult fly. Many flies are pests, disease vectors, or parasites of animal and humans, either as adults or in their larval stages. Even nonbiting flies, such as the autumn house fly and headfly, are an irritation to grazing livestock, interfering with their resting and feeding and causing loss f condition. Flies with bloodsucking adult stages, for example, the buffalo gnat, gadfly, A. G. Arijo
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keds, midges, stable flies, and horn flies, inflict a painful bite causing distress and interrupting feeding. Cattle may be provoked into gadding, with the risk of exhaustion or injury and consequent reduction in milk yield. Sheep may rub their fleece to alleviate the irritation, thus damaging the wool. The fly-inflicted wounds attract other flies and may become secondarily infected; allergies may develop. Flies are also important vectors of disease. The non-biting house fly Musca domestica and the bluebottle, Calliphora spp. visit faeces and human food, and the lays eggs there on meat, spreading such diseases as bacterial dysenteries and gastroenteritis. The house fly and headfly play an important role in the spread of mastitis in cattle: the bacteria are picked up in fly excreta and saliva on an infected udder and carried to uninfected cows. Other bacterial and virus disease transmitted by flies include bluetongue in sheep (carried by midges and mosquitoes), equine encephalomyelitis (mosquitoes), and anthrax (house flies, gadflies, and stable flies). Parasites too are transmitted by flies. For example, some act as intermediate hosts for parasitic nematode worms, which cause diseases such as filariasis in humans, dirofilaria in dogs (mosquito), and onchocerciasis (buffalo gnat or blackfly). Others transmit protozoan blood parasites that cause diseases, including surra in domestic animals (gadflies and stable flies), sleeping sickness in humans and nagana in cattle (tsetse flies), malaria (mosquito), and leishmaniasis (sandfly). The larval stages of certain flies are themselves parasites. For instance, green-bottle fly larvae cause blowfly strike of sheep and warble fly larvae damage the hides and meat of cattle. Fly control measures are thus of great economic and veterinary importance. Nets give some protection but many flies are small enough to pass through. Insect repellents can be used either on screens in animal house or sprayed directly onto the animals sprayed directly onto the animals themselves or used in special repellent ear tags. They have a limited residual effect and must be renewed regularly. A. G. Arijo
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Suitable insecticides can be used for spraying animal houses, or used in dips or sprays for the animals themselves, or applied as dressings to wounds. Effective control may entail the clearance, drainage, and selective spraying with residual insecticides of local fly breedinggrounds. Biological methods of control, such as the introduction of fly parasites or of sterile males, may also be used. FOOT MANGE (itchy leg) It is a type of mange affecting the lower limbs of the horse and due to the mite Chorioptes equi. The condition is also called Itchy leg. The resulting irritation causes shuffling, stamping, and bitting of the feet and may be sufficiently severe to interfere with the animal’s rest.
FORAGE MITE A mite that normally lives in forage but is sometimes an ectoparasite of horses, damaging the skin. Examples: Tyroglyphus and Glyciphagus.
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G GADFLY It refers to a large size fly, also known as the horse fly, deer fly. Gadflies have powerful wings and are strong fliers. The female flies feed on the blood of humans and range of domestic animals. Horses and cattle are considered as host of choice. Gadflies lay eggs near water streams under stones etc. The eggs hatch into caterpillar-like larvae, which develop into pupae in nearby soil or mud. Gadflies are found world wide (e.g. Chrysops, Tabanus, and Haematopota). They are active during daylight, especially on hot sultry days, and their biting is very painful, which may cause animals to stampede, or gad. This can cause reduction in milk yield in cattle. They also transmit a number of serious diseases, such as Surra, Equine Infectious Anaemia, and Anthrax. Control of Gadflies is difficult. However, regular use of oil or paraffin makes it difficult for larvae to breath and they die. Adult flies may be controlled with regular use of insecticide. GIARDIA A genus of flagellate protozoa infecting man and animals all over the world. The parasites in this genus settles in the small intestine of mammals, and causes a disease called giardiasis. The parasite has no A. G. Arijo
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intermediate host and the life-cycle is direct. Contaminated food and water is the main source of spread. On reaching in the intestinal lumen the parasite forms cysts which are released out of body through feces. GIARDIASIS The disease caused by Giardia parasites is called giardiasis. The main symptom of disease is diarrhoea. The disease is very common in humans in humans of warmer countries of world. In animals the disease is uncommon but probably occurs most often in dogs. The clinical confirmation of disease is necessary because diarrhea is a common symptom. The Diagnosis is confirmed by the detection of the organisms in faeces GONGYLONEMA A genus of parasitic nematodes found in the oesophageal wall or stomach (rumen) of ruminants and other grazing animals. G. pulchrum occurs in cattle, sheep, goats, buffaloes, horses, and camels; G. verrucosum is found in ruminants in tropicals regions. The adult worms inhabit tumours on the gut wall. Eggs are passed in the faeces and are ingested by dung beetles, in which the larvae develop. The larvae are then passed or the beetles may be eaten directly by the host. Infestation does not cause disease. Humans may be infested by accidental ingestion of the beetles. The larvae do not develop properly but may be eaten directly by the host. Infestation does not cause disease. Humans may be infested by accidental ingestion of the beetles. The larvae do not develop properly but may cause creeping eruption in the cheeks and lips.
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H HABRONEMA A genus of parasitic nematodes that infest horses and cause the disease habronemiasis. There are three main species: H. macrostoma, H. macrostoma, and H. muscae. The adults are found in the gut, while the larval stages may be found in open wounds. The eggs are passed in the faeces and ingested by the larvae of stable flies and house flies, in which they themselves develop into larvae; they remain with the fly larva until it becomes an adult fly. The horse becomes infested either by swallowing the adult fly or by migration of the nematode larvae from the fly’s mouthparts to open wounds on the horse. HABRONEMIASIS A disease of horses caused by parasitic nematodes of the genus Habronema. The adult worms are found in nodules on the stomach wall or embedded in the gastric mucosa, depending on the species of parasite involved. The result is chronic inflammation of the stomach, which interferes with gastric function. The larvae are spread by flies and may infest open wounds, causing a condition known as summer sores. The horse may bite the affected part until the skin is quite raw, and larvae may be transferred to the horse’s mouth and be swallowed to resume normal development to the adult. In Australia a granular conjunctivitis known as swamp cancer is believed to be caused by Habronema
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larvae. There may be also be a growth on the inner corner of the eye. Treatment is with ivermectin. HAEMONCHUS A genus of parasitic nematodes containing members that cause parasitic gastroenteritis in livecattle in warmer gregions, and H. contortus is important in sheep. The adults are found in the mucosa of the host’s faeces. When the larvae have hatched and developed they migrate up the leaves of wet herbage, from where they are ingested by the host to settle in the abomasum. In ewes immunity to the worms may decrease before parturition causing an increase in egg production, which places lambs at an increased risk of infestation. Lambs may also be infested by larvae from a previous year, and can suffer severe anaemia in the summer months before natural immunity has time to develop. Affected animals may be constipated and suffer oedematous swelling at the throat (‘bottle jaw’). Treatment is by thiabendazole, fenbendazole, etc.; ivermectin is an excellent newer drug. HEADFLY Head flies or plantation flies, Hydrotaea irritans, are nonbiting flies found in large numbers in northern European countries, especially Denmark and Great Britain, where they are pests of cattle, sheep, and other livestock. This fly resembles the house fly and is ~4–7 mm long. The thorax is
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black with gray patches, the abdomen is olive green, and the wing bases are orange yellow. Head flies are a nuisance to domestic animals and people because they are attracted to the mouth, nose, ears, eyes, and wounds to feed on secretions. Unlike other Hydrotaea spp, H irritans produces one generation per year, with three larval instar stages. Eggs deposited in late summer hatch out larvae within a few days. The saprophagous stage is brief, before development to the stage that is predatory on other insect larvae. Overwintering occurs as late-stage larvae. Adults are most active from early June until late September and are common in the vicinity of thickets or woodlands in which they shelter between periods of feeding. Pathology In Great Britain, sheep are mainly affected. Large swarms of flies, attracted by the movement of animals, congregate to feed on secretions from the eyes and nose and on the cellular debris at the grown horn base. To alleviate the persistent irritation, sheep scratch and rub their heads, resulting in raw wounds or “broken heads,” especially on the poll. Flies, attracted by the blood, settle on these selfinflicted lesions and extend the margins by their feeding activity. Sheep of all ages are involved, but breeds with horns and without wool on the head are most severely affected. Head flies also attack people, deer, horses, cattle, and rabbits. Although no corresponding broken head lesions develop in cattle, the occurrence of summer mastitis (due to Corynebacterium pyogenes) and the seasonal activity of head flies are closely associated, especially in Denmark. Head flies may also be involved in the spread of myxomatosis in rabbits. Treatment and Control A. G. Arijo
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The development, emergence, and congregation of head flies, which occur away from farm areas, preclude the traditional methods of insecticide spraying of generalized breeding sites and resting habitats. Control at the point of contact between the feeding adult insects and the mammalian hosts is also limited in value. With sheep, the retention of organophosphate compounds or pyrethrin derivatives on the susceptible head areas is of short duration, which necessitates impractical reapplications in free-ranging animals. Use of insecticide-impregnated ear tags in cattle decreases the incidence of summer mastitis, presumably by reducing transmission by head flies. Removal of livestock from infested locations during the fly season is the only completely effective way to prevent damage. Once broken heads have occurred, the housing of sheep is the only successful method to stop further fly damage. HELMINTH A general name for any parasitic Worm, i.e. One of the flukes (trematodes), tapeworms (cestodes) or roundworms (nematodes). HISTOMONAS A genus of protozoan parasites containing a single species, H. meleagridis with one or more flagella. It varies on size (from 4-30 um diameter) And shape depending on the stage in its life cycle and the site extremely A. G. Arijo
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common and normally benign parasite of the large intestine of domestic fowls and turkeys, but it may occasionally invade the intestine wall and liver provoking severe disease in turkeys. Cysts are shed in the faeces of infected birds but usually do not survive direct transmission to other birds by the oral route. Instead, the parasite has evolved a remarkable symbiotic relationship with the parasitic roundworm Heterakis gallinarum. This common nematode inhabits the caecum with Histomonas, it ingests. The protozoan invades the ovaries of female roundworms and passes from the host within the worm eggs, which are excreted in faeces. Within the thick-shelled egg Histomonas can remain viable in the soil for many months or even years. When the eggs are ingested by other birds the worm larvae hatch and the histomonads are liberated and able to parasitize their new host. As a further refinement to this life cycle, earth-worms can ingest the Heterakis eggs, which in turn contain Histomonas. In this way the spread and survival of the histomonads may be further enhanced. Many outbreaks of histomoniasis in free-range turkeys were historically associated with heavy rain, which brought large numbers of earthworms to the soil surface. HOOKWORM The common name for nematodes belonging to the family Ancylostomidae. They are intestinal parasites characterized by having a mouth capsule with ventral teeth or plates inside the opening. They normally have a direct life cycle and can infect their host by direct penetration of the body surface or by ingestion. Hookworms cause a chronic debilitating A. G. Arijo
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condition and are particularly important in humans in tropical areas. HORN FLY The common name of Haematobia irritans comes from the fact that these flies often cluster in the hundreds around the base of the horns of cattle. This major pest of cattle is found in most cattle-producing areas of the world. Populations are common in Europe, North Africa, Asia Minor, and the Americas. Throughout North America, horn flies are found almost exclusively on cattle, but they will feed on horses, sheep, goats, and wildlife. Horn flies are found in much larger numbers in Pakistan as well. Adult horn flies spend their entire life on their host, and females leave only to oviposit eggs on fresh cow feces, where larval and pupal development occurs. In the southern USA, the life cycle can be as short as 1 wk, but in cooler climates and in the spring or fall, development can take 2–3 wk. In some warmer areas. Horn flies reproduce throughout the year. When the air temperature is
