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Current Perspectives on Rabies Postexposure Prophylaxis Agathe Blaise1 and Philippe Gautret1,2* 1
Assistance Publique Hôpitaux de Marseille, CHU Nord, Pôle Infectieux, Institut HospitaloUniversitaire Méditerranée Infection, 13015 Marseille, France; 2Aix Marseille Université, Unité de Recherche en Maladies Infectieuses et Tropicales Emergentes [URMITE], UM63, CNRS 7278, IRD 198, Inserm 1095, Faculté de Médecine, 27 bd Jean Moulin, 13005 Marseille, France Abstract: Rabies is a zoonose affecting wild and domestic animals and transmitted to humans through bites or scratches, causing over 60,000 human deaths, annually. The disease results from the transmission of a neurotropic virus leading to invariably deadly encephalitis. The post-exposure prophylaxis consists of careful washing and disinfection of the wound, antibiotherapy and tetanus prophylaxis when needed. Furthermore, rabies vaccine and rabies immunoglobulin [RIG] administration should be applied according to the type of wound, and the animal involved, according to the WHO protocols that are regularly updated. Unfortunately it is sometimes difficult to obtain RIG in some countries due to their high cost, leading to suboptimal treatment and possible death. Also, observance can be weak, due to the number of repeated visits required with protocols [up to five visits over 28 days]. These limitations justify research on new vaccines which were not conclusive at the moment. New RIGs are under development, including a monoclonal antibody cocktail which is more promising in a near future. Finally, vaccination protocols are in the way of being shortened in given conditions. Further studies are needed to validate these new practices.
Keywords: Humans, post exposure prophylaxis, rabies immunoglobulin, rabies, recommendations, vaccines. INTRODUCTION Rabies is a viral zoonosis affecting domestic and wild mammals, considered as reservoirs and vectors, and spread to humans is usually through a bite or scratch. Rabies is found on all continents except Antarctica, but 95% of human deaths related to this disease occur in Asia and Africa, notably in India, China, Bangladesh Pakistan, Myanmar, Nepal and Indonesia with recent outbreaks in Flores and Bali. There were 61,000 deaths recorded by WHO in 2010 [this figure is probably underestimated], mainly transmitted by dogs and affecting children in 60% of cases [1, 2]. The disease results from the transmission of the virus RNA single-stranded order Mononegavirales, family Rhabdoviridae, genus Lyssavirus via an animal phase of viral shedding, through saliva during a bite, scratch, or when licking injured skin or mucosa or very rarely through aerosol [3, 4]. There is no transmission through intact skin. Inter-human contamination is exceptional, described in some patients through organ transplant from infected donors [5]. The incubation period varies from less than one week to several years, but is usually between one and three months, rarely more than a year. The first signs associate fever and pain at the site of the bite or scratch that enabled the transmission of the disease. Neurotropic virus spreads through the nerve ending in the central nervous system, causing encephalitis, almost always invariably fatal in 7-10 days after the first *Address correspondence to this author at the Aix Marseille Université, Unité de Recherche en Maladies Infectieuses et Tropicales Emergentes [URMITE], UM63, CNRS 7278, IRD 198, Inserm 1095, Faculté de Médecine, 27 bd Jean Moulin, 13005 Marseille, France; Tel: 0033 [0]4 91 96 35 35/36; Fax: 0033 [0]4 91 96 89 38; E-mail:
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symptoms [6]. There are two forms of rabies [7], one called "furious" involving hyperactivity, hydrophobia, leading in a few days to a cardio-respiratory arrest. The other form called "paralytic" combines a flaccid paralysis of the limbs, progressing to coma and death. This form is often not associated with the diagnosis of rabies, making a probable underreporting of cases worldwide. Unlike other viruses, lyssavirus is neurotropic, and does not cause viremia. Confirmation of the diagnosis is obtained by the combination of a consistent clinical form, and the presence of viral RNA in saliva or hair follicles at the neck, rich in nerve endings [8, 9]. Genetic analysis of lyssavirus then provides important epidemiological evidence, determining the viral species, its usual reservoir and likely geographical origin [1, 10]. Post-exposure prophylaxis [PEP] starts with a local cleansing of the wound and use of disinfectant as soon as possible after the potentially contaminating contact, effective vaccination as recommended by WHO [2], and possibly the administration of rabies immunoglobulin. When applied in due time before the clinical phase of rabies, this treatment is highly effective in preventing the disease. Worldwide, more than 14 million people receive PEP annually after being bitten by a potentially rabid animal. MATERIALS AND METHODS We conducted a bibliography search using PUBMED search engine with the following key words: "rabies" "postexposure prophylaxis", "vaccines" and "immunoglobulin" bringing 124 results after filtering publications concerning only "humans" and publications under 35 years. All of these
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items have been revised and refined, and 39 items were included in this review. CLINICAL IMPLICATION PEP Cleaning the wound caused by bites, scratches or damaged mucosa should be as rapid as possible. It consists of a thorough wash using running water with mild soap and cleaning with a virucidal substance. An optional suture should be avoided or should follow the injection of immunoglobulin if absolutely necessary. Then modalities for post-exposure rabies prophylaxis should be discussed. It combines vaccination with different vaccines and protocols, and administration of immunoglobulin depending on the type of bite. We first detail the vaccines and immunoglobulin, currently existing and ongoing developments, and finally the protocols currently recommended, and the overhangs for these protocols. VACCINES Attenuated vaccines against rabies appeared in 1885, with the technique of Louis Pasteur [11]. With a constantly changing technical production until the 1950s, the last vaccines from cell culture techniques are inactivated vaccines [12, 13]. The use of vaccines for over 40 years has shown the efficacy and safety of these products, as used in pre-exposure prophylaxis and post exposure. Associated with washing of the wound, and possibly immunoglobulin, they guarantee the absence of rabies disease development among individuals exposed to the virus. There are different types of vaccines [12], mammalian nerve tissues vaccines, avian tissue vaccines, and cell culture derived vaccines. Products by cell culture or CCEEVs [Cell Culture and embryoned egg-based vaccines rabies] vaccines include: •
PDEV on embryoned duck eggs [purified duck embryo vaccine] [1950].
•
HDCV on human cells [human diploid cell vaccine] [1964].
•
PCECV on embryonic chicken cell [purified chick embryo cell vaccine] [1965].
•
PVRV on Vero cells [purified Vero cell rabies vaccine] [1984] [12, 13].
After cell culture, the virus sample is concentrated, purified, inactivated and lyophilized. Vaccines can be used for at least 3 years, if stored in a cool [2-8 °C] and dark area. The vaccine should be used within 6 hours after reconstitution [2]. The WHO issues recommendations for the definition, production and control of the production of these vaccines, through the WHO Expert Committee on Biological Standardization [14]. Vaccines from nerve tissue are less immunogenic, induce more side effects and are not recommended by the WHO since 1984 [15]. Nevertheless, some South American and Asian countries continue to use it and are encouraged by the WHO to gradually replace their type of vaccine [16].
Blaise and Gautret
The vaccines are presented in single-dose form, from 0.5 to 1 ml, for intramuscular injection. A sterile solvent allows reconstituting the vaccine, containing at least 2.5 IU/vial for potency [2]. In children over 2 years and adults, the vaccine is injected intramuscularly in the deltoid region, while before the age of 2 years; it should be injected in the anterolateral thigh. The buttock should not be the site of vaccination for rabies vaccines since it is shown that vaccination induces lower vaccine response [17]. Some of intramuscular vaccines might be used intra-dermally, which is used in developing countries [Asia and South America] for reasons of cost alternative. Indeed, this mode of administration uses significantly less product [0.1 ml per site, multisite injections] [2, 18], confer equal immunogenicity and safety. These two routes are equivalent in terms of immune response. Intradermal administration may be technically more demanding than intramuscular injection, and may have some difficulties in implementation, although it is widely used in some countries in Asia. WHO proposes in annex of its recommendations technical assistance by the explanation of the realization of this intradermal injection [19]. Only two of the three vaccines available CCEEVs can be used intradermally: PVRV on Vero cells [purified Vero cell rabies vaccine] and PCECV on embryonic chicken cell [purified chick embryo cell vaccine]. For the intradermal route, the recommended injection zones are: deltoid, lateral thigh, suprascapular region [20]. Generally, these vaccines are well tolerated. Erythema, edema, and pain may occur at the site of vaccination in 3545% of vaccinated people, especially when the intradermal route is used. General symptoms may also appear with fever, headache, and gastrointestinal disorders in 5-15 % of vaccinated people. Rarely, significant allergic reactions or Guillain-Barré-like syndrome were observed [2]. Provided the administration of 2 boosters following an eventual new exposure, a long-term duration of protection is obtained, following a complete protocol. This is independent of the route of administration of the vaccine, and neutralizing antibodies titration. Revaccination at regular intervals is no longer relevant, outside the context of certain high-risk occupations [21, 22]. The rabies vaccines have the disadvantage of having to be administered several times, making it a cost issue and a potential compliance problem associated with repeated medical visits. What is expected of a new vaccine is important immunogenicity, with a single effective dose, associated with the safety and the ease of cell culture, with an affordable cost. The rabies virus is composed of a single strand of RNA which encodes five proteins including nucleoprotein [N], phosphorprotein [P], matrix protein [M], glycoprotein [G] and RNA polymerase [L]. The G glycoprotein is exposed on the surface of the virus, and is therefore one which has a large number of antigen sites available for the link with neutralizing antibodies [12, 13]. The different tracks of new vaccines are the following: DNA vaccines: DNA vaccines offer a thermo stability and interesting cost of production. However, they are less efficient than traditional vaccines, however, one vaccine using a G [glycoprotein gene] modified rabies virus showed higher immunogenicity compared to usual vaccines. These
Current Perspectives on Rabies Postexposure Prophylaxis
new vaccines must be validated by the regulations in terms of production, immunogenicity and safety [12, 13]. Vaccines derived from plant: Several studies have shown that the G glycoprotein may be produced by transgenic plants; these transgenes have been administered orally or parenterally to animal model. However, there are limitations and concern regarding the antigenic response [12, 13]. Recombinant vaccines: Increasingly poxviruses [23] or other viruses such as adenoviruses have been considered for recombinant vaccine research, and are more antigenic than traditional vaccines. However, studies requiring careful longterm evaluation are needed since a potential replication of a recombinant virus is possible. In addition, the oral route is currently the only route of administration, and remains a limitation for human vaccination and seems more adapted in the context of mass vaccination of wild and domestic animals. Inactivated recombinant rabies virus vaccines: Residual pathogenicity is an important problem in immunecompromised patients. The ability to clone the glycoprotein of rabies virus with genetic engineering via bacterial plasmids opens a new way of rabies vaccines production. The use of gene rearrangements, duplication or deletion gives varying degrees of immunogenicity, this line of research is interesting, but the public perception and multiple regulatory problems could make complex the use of these products. These new vaccines induce a satisfactory immune response in small animal models. Unfortunately, they cannot at present compete with traditional vaccines, given their price, and acceptability in humans. Faber et al. [24] shows an example of this approach with a candidate live inactivated vaccine, variant of classical rabies vaccine glycoprotein, interesting for its immunogenicity and nonpathogenic even in immunesuppressed animals. In addition, new adjuvants are evaluated to an economy of material [25, 26]: increasing the immunity induced by vaccination, immunization schedules may be shortened. The use of novel adjuvants is being tested in the context of different vaccine [27]. Two studies show the use of CpG oligodeoxynucleotides [CpG-ODNs] [28] or the microspheres of poly [lactide-co-glycolide] [29] and suggest an increase in the effectiveness of the vaccines currently used, with 3 versus 5 doses usually required [30]. Despite these encouraging results, these studies are done in mice, which do not have the same immune expression patterns as humans. The problem with these innovative vaccines is the difficulty of interpretation of therapeutic efficacy: the antibody levels of vaccination is the only parameter currently measured. Modulation quality of immunity resulting from vaccination using new processes is difficult to assess. Indeed, it uses the CD4 cells, memory B cells, and other parameters, that are not currently measured [25]. IMMUNOGLOBULIN Under certain bite conditions, which are developed further, RIG administration is indicated in addition to the vaccination. Evidence of the effectiveness of these products has been given as the opportunity of a wolf bite in Iran in 1954, making a study in the treatment of 29 bitten patients [3]. Of
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the 18 patients severely bitten to the neck or head, 3 of 5 who received vaccine alone died; while 1 of 13 who received the combination of vaccine and RIG died. This is a passive immunization; the activity is still a short time [half-life of 21 days [3, 31]. RIG should be injected as soon as possible after the bite, ideally at the same time or immediately after vaccination. The entire injection should be done as close as possible to the place of potential rabies inoculation [into and around the wound]. Otherwise, the largest part must be injected nearby the wound, and the rest in a remote site for intramuscular vaccination. The vaccine products and RIG must not be mixed in the same syringe. RIGs are of three different types, human RIG [HRIG], equine RIG [ERIG], and the purified fraction F [ab '] 2 of ERIG. This third form is potentially less immunogenic. The interest of these RIGs, delivered on the site of the bite is to quickly confer protective neutralizing antibodies before the development of active immunity through vaccination. Thus, it is not recommended to inject RIG more than seven days after administration of a vaccination since it could disrupt the immune response. The doses are to deliver RIG of 20 IU/kg body weight for HRIG, and 40 IU/kg for ERIG. If the volume with doses was not significant enough to inject the entire wound, sera could be diluted in physiological serum in order to administer all RIG in the wound [2]. Rare local adverse transient ERIG reactions occur but are transient anaphylactic reactions are described in the ERIG administration, but skin testing prior to administration is not necessary because it does not predict reactions, and no longer recommended [2]. In practice, the administration of these RIGs should be in a technical center prepared to manage anaphylaxis. ERIG should be used without delay where HRIG is not available. One possibility to avoid the use of these RIG is to vaccinate [pre-exposure vaccination] preventively populations likely to be bitten, since the protocol in case of previous vaccination does not use RIG, but only 2 doses of vaccine. This approach could be discussed for patients at risk such as children in rabies-endemic areas. However, it would be ineffective if vaccine supplies are not sufficient to vaccinate the entire target population. In addition, in immuno-compromised patients [HIV, immunosuppressive drugs, immunosuppressive diseases, and malaria chemoprophylaxis], this measure would probably be not effective enough [3]. The high price of these RIGs, low availability of these products, and rare side effects make discussing the possibility of development and use of monoclonal antibody [Mab]. The development of Mab [32] is an alternative to the lack of HRIG or ERIG products, notably in developing areas. Theoretically sufficient stocks of products could be produced at a reasonable cost and tests are currently performed in humans. In 2007, a Mab was isolated from a transgenic mouse, after the work of Sloan et al. [33]. This antibody [Ab], known as Rab1, is able to neutralize all known rabies virus, is inexpensive to achieve, and is stable in production, making it a promising Mab. Todd G Smith et al. [12] refers to the possibility of using Ab to identify mAbs with qualifications in their rabies serum activity. Muller et al. [32] show the strategy of producing 3 cocktails Mab whose efficiency is equal to that of HRIG or ERIG. The ability to create on
16 Infectious Disorders – Drug Targets, 2015, Vol. 15, No. 1
immortalized human cells Mabs avoids the risk of allergic reactions. The production of these Mabs via transgenic plants is also a potential development with significant production related to extensive farming. Bakker et al. [34] in 2008 reported the first data from a phase II study, evaluating a cocktail of Mabs human CL 184 with 2 Mabs, the CR57 IgG1 lambda, and CL4098 IgG1 kappa. Patients tested were from the USA and India, and received an intramuscular dose of CL184 or placebo in a double-blind, randomized, and with increasing doses. In addition, other patients received a dose of CL184 20UI/kg concomitantly with the rabies vaccination. The safe use was the main objective, and neutralizing Ab rate was the parameter monitoring efficacy endpoint. The only reported side effect was pain at the injection in less than 40% of cases. Neutralizing Ab were detected from the first day in some patients until day 21. All patients had a higher 0.5UI/ml from day 14 in those who were vaccinated concomitantly rates, making it an interesting alternative approach to human or equine immunoglobulins. However, several countries have refused to allow phase III studies on exposed patients; considering such studies unethical as we have time proven excellent technology used today.
Blaise and Gautret
•
RIG administration if the indication is used.
The protocols are decided according to the severity of the disease, the patient's status with respect to its immunity, the animal responsible, its place of origin and what is known of the local epidemiology of rabies. The decision also takes into account the possibility of whether or not the animal can be monitored for 10 days, and shows no clinical sign of rabies at the end of this period. In this case, the post-exposure prophylaxis can be initiated and stopped [2]. The exposure categories are summarized in Table 1. •
Category I corresponds to a licking on healthy skin or contacting potentially contaminating secretions on unbroken skin and no PEP is indicated, since there is no risk of infection.
•
The category II includes the biting of the skin, small scratches, and abrasions in the absence of blood suffusion. Vaccination should be undergone for post-exposure prophylaxis, combined with RIG if the patient is immuno-compromised.
•
Category III corresponds to trans-dermal bites or scratches, licks on broken skin, mucous membrane contamination with infected saliva or any contact with bats. All these situations require vaccination associated with the administration of RIG, on different sites as soon as possible.
THE CURRENT PROTOCOLS Post-exposure prophylaxis consists of the realization [2]: •
Disinfection as soon as possible after the bite or scratch, which is an integral part of this approach, consisting of washing with water and soap, detergent or virucidal substance.
There is no contraindication for vaccination, as the lethal risk to the possible development of rabies is great. Vaccination in children, pregnant women, and immuno-compromised patients, even in pediatrics is possible and recommended if the f treatment is indicated.
•
Realization of the vaccination according to WHO recommendations.
The main situations and their management are recalled in Tables 1 to 3.
Table 1.
Recommended rabies post-exposure prophylaxis [PEP] according to type of exposure. Who 2013. WHO expert consultation on rabies. Second report.
Category of exposure
Type of exposure to a domestic or wilda animal suspected or confirmed to be rabid, or of unknown status
Recommended PEP
Simple contact with animals I
Contact of intact skin with secretions or excretions of a rabid mammal including human.
None
Administer vaccine as soon as possibleb II
Nibbling of skin, minor abrasions and scratches without bleeding
Transdermal bitesd or scratches III
Contamination of broken skin or mucous membrane with saliva Bat bite or scratch or exposure of a mucous membrane to bat secretion or excretion
a
Stop PEP if animal remains healthy throughout an observation period of 10 daysc or is proven to be negative for rabies following laboratory investigation Administer rabies vaccine and immunoglobulin, as soon as possible. Rabies immunoglobulin can be injected up to 7 days following the first vaccine injection. Stop PEP if animal remains healthy throughout an observation period of 10 daysc or is proven to be negative for rabies following laboratory investigation
Exposure to rodents, rabbits, or hares does not routinely require rabies PEP.
b
If an apparently healthy dog or cat is placed under observation, PEP may be delayed.
c
This observation period applies only on dogs and cats. Other potentially rabid domestic and wild animals should be euthanized for laboratory investigation.
d
Bites on the head, neck, face, hands and genitals are category III exposures because of the rich innervation of these areas.
Current Perspectives on Rabies Postexposure Prophylaxis
Table 2.
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Rabies post-exposure prophylaxis [PEP] schedules – United States, 2010 [35].
Vaccination status
PEP
Regimen
Not previously vaccinated
Wound cleansing
Immediate thorough cleansing of wounds with soap and water and a virucidal agent when available.
Human rabies immune globuline [HRIG]
Administer 20 UI/kg body weight as much as possible into the wound and any remaining volume intramuscularly [IM] at an anatomical site distant from that of vaccine administration.
Vaccine
Inject human diploid cell vaccine [HDCV] or purified chick embryo cell vaccine [PCECV], 1.0 mL, IM, 1 each on days 0, 3, 7, and 14 a.
Wound cleansing
Immediate thorough cleansing of wounds with soap and water and a virucidal agent when available.
HRIG
None
Vaccine
Inject HDCV or PCECV, 1.0 mL, IM,1 each on days 0 and 3.
Previously vaccinatedb
a
For immunosuppressed individuals, rabies PEP should be administred using 5 doses of vaccine on days 0, 3, 7, 14 and 28. b Any person with a history of pre-exposure vaccination with HDCV, PCECV, or rabies vaccine adsorbed [RVA]; prior PEP with HDCV, PCECV, or RVA; or previous vaccination with any other type of rabies vaccine and a documented history of antibody response to the prior vaccination.
Table 3.
Comparison of selected rabies post-exposure regimens adapted from Warrell MJ [39]. Days of injection Superscript: number of sites injected
Vaccine regimen &route
Visits to clinic
Total vaccine used
5
5
3
4
4
4
Post-exposure [+RIG day 0] in previously unvaccinated individuals IM 5 doses
0
IM 2-1-1
0²
IM 4 doses [CDC]
0
3
7
2-sites ID
0²
3²
7²
28²
4
