of raccoon (Baylisascaris procyonis) or skunk. (B. columnaris) ascarid larvae has been reported in man, domestic and wild mammals, and 13 species of birds (1) ...
Encephalitis attributed to larval migration of Baylisascaris species in emus Jacek M. Kwiecien, Dale A. Smith, Doug W. Key, Janet Swinton, Laura Smith-Maxie Verminous encephalitis resulting from the migration of raccoon (Baylisascaris procyonis) or skunk (B. columnaris) ascarid larvae has been reported in man, domestic and wild mammals, and 13 species of birds (1). In the definitive host, these parasites undergo entero-hepatic-pulmonary migration that rarely results in clinical disease. Infected hosts shed large numbers of eggs in their feces; these eggs are highly resistant to environmental or chemical degradation, and remain infective for long periods (1). Infection of other species may result in widespread larval migration and significant clinical disease. In birds, reported lesions have been confined primarily to the central nervous system
(CNS) (2-9).
In July of 1990, two emu chicks (Dromaius novaehollandiae) were presented to the Veterinary Teaching Hospital (VTH), University of Guelph. These birds were from a farm with three types of ratites on the premises: emu, ostrich, and rhea. Breeding pairs of emus were kept in outdoor pens. Eggs were artificially incubated and chicks, grouped in the order of hatching, were held in indoor pens with access to outdoor runs. Straw bedding, purchased commercially and stored on the farm, was used indoors; the outdoor pens were floored with gravel. Thirty-five emu chicks, ranging in age from one week to five months, were present at this time. Four of a group of six, five-to-twelve-week old birds were exhibiting varying degrees of incoordination, splayed legs, wobbling, falling over, and "walking as if drunk". The two most severely affected birds were brought to the VTH for evaluation. Both had clinical signs for several weeks, without obvious improvement or deterioration. Bird 1 was approximately two months of age. It was severely incapacitated, was often in lateral recumbency, and needed support in order to eat. Appetite, prehension, and deglutition of food were normal, as were other cranial nerve functions and demeanor. The gait was very difficult to assess. The bird would not walk if held and would only occasionally struggle to its feet, stand fully erect, walk a few steps in a normal gait and posture, and collapse suddenly, at which time muscle tremors appeared in the limbs. Postural and attitudinal reactions of the limbs could not be performed by the bird. A weak flexor reflex was elicited in both pelvic limbs. Pain sensation to the limbs was present. Severe muscle weakness was the predominating clinical impression. Hematological abnormalities included elevation of Can Vet J 1993; 34: 176-178
Department of Pathology (Kwiecien, Smith) and Department of Clinical Studies (Smith-Maxie), Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1;
Virology Laboratory (Key, Swinton), Veterinary Laboratory Services, Ontario Ministry of Agriculture and Food, P.O. Box 3612, Guelph, Ontario NIH 6R8. Reprint requests to Dr. D.A. Smith. 176
heterophil count to 20.6 x 109/L (normal total white blood cell count 5.5 x 109 ± 1.9/L, normal heterophil percentage 62.6 ± 7.6) (10), and elevation of serum creatinine phosphokinase activity at 1,213 U/L (normal 688 ± 208 U/L) (1 1) (Note: normal values given are for ostriches). The bird was euthanized shortly after admission because of the severity of its debility and the poor prognosis for recovery. Bird 2 was three months old, larger, and much more active than bird 1. Its demeanor, cranial nerve examination, spinal reflexes, sensation, and head and neck posture were assessed as being normal. The bird could stand by itself but would sometimes lean against the side of the cage, and would stagger and fall down if it tried to move quickly. The gait was coordinated and normal in height and force. No head tremor was observed. The collapsing episodes were attributed to a loss of balance in addition to a lesser degree of muscle weakness than bird 1. Results of a complete blood cell count and serum biochemical profile were unremarkable. Chloramphenicol succinate at 50 mg/kg ql2h IM (Rogar-Mycine, rogar/STB, London, Ontario), 0.8 mL of B complex vitamins IM (Vit. B Complex, PVU, Victoriaville, Quebec), and vitamin E (10.9 IU/IM) and selenium (0.24 mg/IM) (Dystosel, rogar/STB) were administered. No improvement was noted between admission and euthanasia, 12 days after presentation, when the results of the necropsy on bird 1 became available.
These birds were from a farm with three types of ratites on the premises: emu, ostrich, and rhea. By January 1991, five additional birds had been submitted for necropsy; all had clinical signs of ataxia, incoordination, and muscle weakness. Three birds were euthanized and two died naturally. These birds ranged in age from 10 weeks to five months. Farm records did not allow us to identify whether these animals had been in direct contact with the two initial cases. Complete necropsies were performed on seven birds. All were in good. body condition. No relevant gross lesion was noted. Tissues were fixed in 10%o neutral buffered formalin, embedded in paraffin, sectioned at 5 zm, and stained with hematoxylin and eosin (H&E). Sections of CNS were also stained with luxol fast blue with Holmes (LFB-H) and periodic acidSchiff (PAS). Six to seven coronal sections of the brain of all seven birds, approximately 20 sections of the spinal cord of each of three birds, and lung, liver, kidney, spleen, heart, pancreas, proventriculus, gizzard, and intestines of all birds were examined. Can Vet J Volume 34, March 1993
Hemagglutinating (HA) activity against red blood cells (RBC) of chicken, turkey, sheep, monkey, and guinea pig (pH 6.0, 4°C and pH 7.4, room temperature) was not detected in eggs or tissue culture fluids. Further attempts to isolate virus were made on tissues from two birds euthanized for necropsy. Liver and spleen were trypsinized and cocultured with CEF and primary chick embryo kidney cells (CEK) in media containing 5 Ag/mL of trypsin. Brain, liver, and splenic tissues, prepared by conventional grinding technique, were suspended in similar media and inoculated onto CEF cells. Vacuolation was seen in cell cultures of brain and kidney at four to seven days postinoculation in passages 2, 3 and 4. Vacuolation was not seen in control cultures which were maintained with the same concentration of trypsin. Changes were not seen white cerebellar of deep section Figure 1. Histological matter of an emu with severe imbalance. A focal, intense in the liver and spleen tissues cocultured for four accumulation of foamy macrophages containing cytoplasmic passages with CEF and CEK cells. Hemagglutination granulation is present. This lesion was considered indicative studies of tissue culture fluids (pH 6.0, 4°C) with both of recent larval migration. PAS, bar 55 rim. Inset: cross chicken and turkey RBCs were negative. Specific section of nematode larvae, presumably Baylisascaris sp. pathogen free egg embryo mortality was seen on the H&E. Bar 42 itm. second passage with suspensions of liver, lung, and brain tissue, and on third passage with spleen and cerebellar the to confined were Significant lesions kidney. Gross lesions were not evident in any affected peduncles, deep cerebellar white matter, and adjacent embryo. Again, egg fluid contained no HA activity. cerebellar folia. Six of seven emus had multifocal to Direct electron microscopic examinations of both egg disruption by characterized malacia of diffuse areas also negative. The significance fluids tissue and and vacuolation of the neuropil, axonal swelling, and of the vacuolationwere passages of inoculated CEF early of loss of myelin. Five of these six birds had rounded, cell cultures and the embryo mortality in inoculated PAScontaining of macrophages foci cellular densely established. was not SPF eggs positive granules (Gitter cells) in some malacic areas (Figure 1). Diffuse microgliosis and leukocytic infiltrates of the neuropil were accompanied by perivascular cuffing with lymphocytes, macrophages, The most consistent initial microscopic finding plasma cells, and, rarely, granulocytes. Segmental loss in our study was perivascular cuffing by of Purkinje cells and granular neurons and neuronal leukocytes similar to that seen in mononuclear necrosis were evident in the cerebellar folia adjacent Perivascular birds. viral infections. in all six to inflammatory lesions cuffing and adjacent axonal swelling and myelin loss were found in the brain stem of three birds, one of Serological tests were conducted on 15 sera from the which also had dense foci of accumulation of Gitter cells, and in the cerebrum of two birds (one of the six affected flock, including bird 2. These included hemagjust described and the seventh bird). In the cerebellum glutination inhibition for antibodies to the viruses of of one bird, three cross sections of a nematode that Newcastle disease, Yucaipa, avian paramyxovirus measured approximately 60 Am in diameter were types 3 and 6, eastern and western equine encephalitis, found (Figure 1, inset). Each of the cross sections con- Highlands J, St. Louis encephalitis, and Powassan; tained a single pair of prominent lateral alae, one pair enzyme-linked immunosorbent assay for antibodies to of large excretory glands, and a centrally located the viruses of avian encephalomyelitis and infectious intestinal tube lined with nine low columnar epithelial bursal disease; and agar gel diffusion for avian cells. The larvae were not surrounded by tissue reaction influenza. No antibodies were detected. The clinical signs and lesions described here are conbut the next caudal section contained tract-like foci of necrosis surrounded by intense, diffuse mono- sistent with reports of verminous encephalitis nuclear cellular infiltrates. Lesions were not noted in attributed to infection with B. columnaris in an emu (8), and of an ostrich and two emus infected by B. prothe spinal cord sections. Bacterial organisms were not isolated from the liver, cyonis (9). The early signs observed at the farm suglung, kidney, spleen, and brain of one emu which died gested a problem of imbalance and incoordination that was consistent with either vestibular or cerebellar naturally. and Muscle weakness was the overwhelming on spleen, dysfunction. brain, was attempted Virus isolation bursal tissues from bird 1. Tissue suspensions were clinical problem by the time bird 1 was examined at inoculated into specific pathogen free (SPF) hen's eggs the VTH. Bird 2 had some imbalance and incoordinaby allantoic and chorioallantoic membrane routes and tion that could have been due to cerebellar ataxia. onto primary chicken embryo fibroblast (CEF) cell cul- However, neither a head tremor nor hypermetria were tures. Significant lesions were not seen on three egg observed. The paucity of literature on neurological passages. Vacuolation of CEF cells was seen on days dysfunction in emus makes it necessary to extrapolate 4-6 postinoculation in passage 2 and 3 of the splenic from other species. Total ablation of the cerebellum and bursal tissues, but was not evident in later passage of birds (12) will produce all the signs of cerebellar levels 4 and 6. Inclusions were not seen in H&E stained ataxia observed in domestic animals. A detailed culture slides of the cells at the affected passage levels. neurological examination at the onset of illness in birds Can Vet J Volume 34, March 1993
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1 and 2 was not possible; the lack of head tremor and weakness, ataxia, and imbalance. Neurohistopatholhypermetria later on could be attributed to compen- ogical examination revealed multifocal areas of satory mechanisms (13) which were facilitated by the malacia and tracts in the cerebellar peduncles, adjacent multifocal nature of the disease process. Prolonged brain stem, and deep cerebellar white matter which recumbency, inadequate food intake, or undetected were similar to lesions in birds examined previously. spinal cord or brain stem lesions could all have con- The spinal cord was not affected. A preventive treattributed to the terminal muscle weakness. Clinical ment program with ivermectin administered every six examination early in the course of disease may allow weeks was altered to more frequent administration after recognition of regional dysfunction and guide subse- the presumptive diagnosis of verminous encephalitis quent histopathological examination. was made. The most consistent initial microscopic finding in With the increasing frequency with which ratites are our study was perivascular cuffing by mononuclear being raised in Canada, it is important that leukocytes similar to that seen in viral infections. After veterinarians and pathologists include verminous viral isolation and serological studies were negative, encephalitis in the list of causes of neurological synexamination of multiple additional sections of dromes in these birds. cerebellum revealed parasitic tracts in five birds and nematode cross sections in one. These lesions were similar to those described by Kazacos et al (8,9). Other Acknowledgments reports on the migration of Baylisascaris sp. larvae in We thank Dr. K. Duval-Hudelson for clinical care, birds describe nonsuppurative meningoencephalitis H. Coates and H. Winter for preparation of histoland malacia, with most severe lesions in the cerebellum ogical specimens, T. Eaton for photography, and (2-9) and less severe involvement of the medulla Dr. W. Korver for providing information on problems oblongata (2,5,7), pons (7), midbrain (3,4), and occurring after our involvement with the farm ended. cerebrum (2,3,7). The localization of the most severe Arbovirus study was kindly conducted by Dr. H. and characteristic lesions in the cerebellum emphasizes Artsob, Zoonosis Section, Laboratory Centre for the importance of including this region of the brain Disease Control, Health and Welfare Canada, Ottawa. for microscopic examination. Although cross sections cvJ of parasites were also seen in previous reports on spontaneous (3-9) and experimental (2) infections, finding References of the actual agent may be the exception. A lack of KR, Boyce WM. Baylisascaris larva migrans. J Am inflammation surrounding cross sections of parasites 1. Kazacos Vet Med Assoc 1989; 195: 894-903. has been reported previously (4). The identification as 2. Kazacos KR, Wirtz WL. Experimental cerebrospinal nematodiasis due to Baylisascarisprocyonis in chickens. Avian Baylisascaris sp. of the parasites that we observed was Dis 1983; 27: 55-65. based upon the characteristic morphology, size (14), 3. Kazacos KR, Kazacos ER, Render JA, Thacker HL. and high pathogenicity, but was not definitive as intact Cerebrospinal nematodiasis and visceral larva migrans in an worms were not examined. Australian (Latham's) brush turkey. J Am Vet Med Assoc 1982; The owner of the flock was informed that a Bayli181: 1295-1298. sascaris sp. parasite, likely of raccoon origin, was 4. Sass B, Gorgacz EJ. Cerebral nematodiasis in a chukar patridge. J Am Vet Med Assoc 1978; 173: 1248-1249. responsible for the problem in the birds. Raccoons had 5. Richardson JA, Kazacos KR, Thacker HL, Dhillon AS, Winterbeen seen on the premises, although not in direct confield RW. Verminous encephalitis in commercial chickens. Avian tact with the animals. Extensive efforts have since been Dis 1980; 24: 498-503. made to prevent access of raccoons to straw storage 6. Winterfield RW, Thacker HL. Verminous encephalitis in the Avian Dis 1978; 22: 336-339. and animal housing areas. Despite this, in February 7. emu. Reed WM, Kazacos KR, Dhillon AS, Winterfield RW, Thacker 1991, a mature breeding female began to have similar HL. Cerebrospinal nematodiasis in bobwhite quail. Avian Dis clinical signs and was eventually euthanized. The entire 1981; 25: 1039-1046. brain of this bird underwent pepsin digestion and 8. Kazacos KR, Winterfield RW, Thacker HL. Etiology and epidemiology of verminous encephalitis in an emu. Avian Dis Baermann extraction, but parasites were not identified. 1982; 26: 389-391. In February, all birds were placed on a preventive 9. Kazacos KR, Fitzgerald SD, Reed WM. Baylisascarisprocyonis program of ivermectin (Ivomec, MSD Agvet, Kirkland, as a cause of cerebrospinal nematodiasis in ratites. J Zoo /Wildl Med 1991; 22: 460-465. Quebec) per os at 200 ag/kg every second month. In i Levi A, Perelman B, Waner T, van Grevenbroek M, van Creveld April, another adult female breeder began to have 10. C, Yagil R. Haematological parameters of the ostrich (Struthio characteristic clinical signs. She died of complications camelus). Avian Pathol 1989; 18: 321-327. secondary to recumbency one month later but was not 11. Levy A, Perelman B, Waner T, van Grevenbroek M, van necropsied. Whether continued problems were due to Creveld C, Yagil R. Reference blood chemical values in ostriches (Struthio camelus). Am J Vet Res 1989; 50: 1548-1550. recontamination, or to survival of ascarid eggs in the TB. Nervous system. In: Sturkie PD, ed. Avian general environment, remains unknown. After this 12. Bolton Physiology. 3rd ed. New York: Springer-Verlag, 1976: 1-28. incident, the frequency of ivermectin administration 13. DeLahunta A. Veterinary Neuroanatomy and Clinical was increased to once per month. There has been no Neurology. 2nd ed. WB Saunders, 1983: 272. 14. Bowman DD. Diagnostic morphology of four larval ascaridoid subsequent case identified in this farm. nematodes that may cause visceral larva migrans: Toxascaris Recently, however, an adult emu from a different leonina, Baylisascaris procyonis, Lagochilascaris sprenti, and farm was submitted live to the VTH with signs of Hexametra leidyi. J Parasitol 1987; 73: 1198-1215.
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