RABIES Etiology Lyssavirus of family Rhabdoviridae Epidemiology Occurs i n all farm animals worldwide except Australia and New Zealand. Major zoonoses. Transmitted by bites of infected animal. Many different wildlife are vectors depending on geographic location; vampire-bats in South America, foxes in Europe and North America, skunks in North America, mongoose in Africa, raccoon in the United States recently Signs Incubation period varies from 2 weeks to several months. Cattle - Paralytic form: bizarre mental behavior (yawning, bellowing), incoordination, decreased sensation of hindquarters, drooling saliva, recumbency, and death in 4-7 days. Furious form: hypersensitive, belligerent, then paralysis and death as i n paralytic form. Sheep - Outbreaks common; sexual excitement, wool pulling, attacking, incoordination, and then paralysis. Horses - Abnormal postures, lameness or weakness, depression, ataxia, pharyngeal paralysis, recumbency, hyperesthesia, biting, loss of anal sphincter tone, death in 4-6 days. Pigs - Excitement, attack, twitching of nose, clonic convulsions, paralysis Clinical pathology No antemortem test Lesions Non-su ppurative encephalomyelitis Differential diagnosis list: • Cattle: Lead poisoning, lactation tetany, hypovita minosis-A, listerial meningoencephalitis, polioencephalomalacia, nervous acetonemia • Horse: Viral encephalomyelitis, herpes viral paralysis, cerebrospinal nematodiasis, equine degenerative myeloencephalopathy, protozoal encephalomyelitis, neuritis of cauda equina, horsetail poisoning, Borna, Japanese encephalitis, botulism • Sheep: E nterotoxemia, pregnancy toxemia, lou ping-ill, scrapie • Pig: Pseudorabies, Teschen's disease, Glasser's disease, and other meningitides (E. coli and Streptococcus sU/s). Diagnostic confirmation Fluorescent antibody test of brain. Negri bodies histologically Treatment None. All rabies cases are fatal Control Prevention of exposure. Vaccination of domestic ani mals and wildlife. Quarantine and biosecurity to prevent entry of virus into country ETIOLOGY Rabies is associated with the rabies virus of the genus Lyssavirus of the family Rhabdoviridae.1 The genus is composed of at least six genotypes. It was recognized long ago that the strain of virus known as the ' street' rabies virus differed in some way from 'fixed' strains which had been cultivated for vaccine production (grown in cell culture or passaged through serial generations of laboratory animals) . It is now known that t there are several strains of rabies virus, which are adapted to particular host species but remain infective for any warm-blooded mammal.2 EPIDEM IOLOGY Occurrence Rabies occurs in all warm-blooded animals.1.3 The disease occurs in cattle, sheep, pigs, and horses in most countries, except the insular countries that exclude it by rigid quarantine measures or prohibition of the entry of dogs. However, the genus Lyssavirus can still cause surprises. In 1996 and 1998, two women died in Queensland, Australia, from infections with a newly discovered rabies-related virus (Australian bat lyssavirus) .4 In 2002, a man died in Scotland after contracting European bat lyssavirus rabies indicating that after a century of apparent freedom from rabies, the disease is now enzootic in the UK 4 South America, Latin America and the C aribbean Rabies in cattle is a major economic and public health problem in South America, where vampire bat-transmitted rabies results in cyclic outbreaks. Bovine paralytic rabies is endemic in the tropical regions extending from northern Mexico, to northern Argentina, and on the island of Trinidad.! An outbreak in cattle in Guyana was associated with a large number of bats that had inhabited a culvert that was not cleaned regularly because of excessive rainfall. Europe In Europe, sylvatic rabies is a major problem where the red fox is the prindpal vector. The disease is still spreading from a focal point that developed in Poland in the mid -1930s. It is endemic in Yugoslavia and Turkey, and has spread westward to Germany, Denmark, Belgium, Czechoslovakia, Austria, Switzerland, and France. Spread continues at the rate of about 30-60 km (18-37 miles) per year and the threat to the United Kingdom increases each year. finland had been free of rabies since 1959, but in 1988 sylvatic rabies occurred with the raccoon dog as the vector. Monoclonal antibody indicated the virus was an Arctic-type strain possibly related to the red fox. France reported more than 2000 cases of rabid cattle between 1968 and 1982, and had more cases in sheep than in either dogs or cats during the same time period. In former East Germany, sheep were the second most frequent animal diagnosed with rabies after foxes. Epidemiological studies of rabies in Lithuania from 1990 to 2000 found that rabies among wildlife comprised 54 % with the majority of cases in foxes (27%), followed by raccoon dogs (21 %).5 The incidence of rabies in foxes and raccoon dogs increased over the period of study. Also, the number of humans attacked by domestic animals and wild animals has increased. Africa Rabies occurs in most countries in the African continent, but the reported incidence is surprisingly low for an area with such a high population of wild carnivores. The incidence of rabies, and the range of species involved, is increasing in Africa, and a number of wildlife hosts has been identified, including wild dogs, jackals and mongoose. Because of dislocation of civilian life, rabies in Zimbabwe has increased in prevalence and geographical distribution in recent years. Rabies is now a very serious zoonotic disease in South Darfur, Sudan.!6 South Africa Over a 4-year period, of all the domestic animal rabies cases reported, cattle accounted for one-half of the rabies cases in South African domestic animals. The mongoose accounted for 70% of the wild animal cases reported.7 Widespread distribution of the rabies virus occurs when the young mongooses are evicted from their parents' territory during the winter months, forCing them to scatter over a wide area. This increases the probability of domestic animals coming in contact with rabid animals. Canada The arctic fox variant of rabies invaded most of Canada south of 600N and east of the Rocky Mountains in the early 1950s largely by the migration of arctic foxes into the populated areas.s It died out in most of that range, but persisted for over 40 years in southern Ontario with sporadic incursions into narrow adjacent strips in western Quebec and northern New York. The principal vectors were red foxes (Vulpes vu/pes) and, to a lesser extent, striped skunks (Mephitis mephitis) . During the period 1957 to 1989, Ontario experienced more animal rabies cases than any almost every North American jurisdiction almost every year, and over 95% of those cases were limited to the southernmost 10% of the province's land area.A second major outbreak, involving striped skunks, progressed from North Dakota into the prairie provinces during the late 1950s and 1960s. In the 1990s, the endemic areas in Canada are southern Ontario, which accounts for 85 % of the Canadian diagnoses, and the prairie provinces where rabies is endemic in skunks. In western Canada, the main reservoirs of the rabies virus are skunks, bats, and foxes. In southern Ontario, Canada, the ecogeographic patterns of rabies indicate that townships could be aggregated into 12 rabies units or clusters 9 The units had different behaviors in terms of species composition, persistence, and periodicity. The ratio of rabid skunks to rabid foxes varied between areas which may be due to seasonal factors and urban development. This information is useful for planning rabies control programs. U n ited States Information on rabies surveillance in the United States is published annually by the Centers for Disease Control and Prevention lO-14 From 1999 to 2003, more than 90% of cases occurred in wild animals, 6 to 9% in domestic animal species. The disease occurred in humans, raccoons, skunks, bats, foxes, cats, dogs, cattle, sheep and goats, horses and mules, mongoose, rodents and lagomorphs. Most cases of rabies reported annually in the United States occur among three groups of carnivores: raccoons, skunks, foxes, and among batsY However, between 1960 and 2000, a total of 2851 cases of rabies in 17 other carnivore taxa were reported to the Centers for Disease Control and Prevention, Atlanta, Georgia lS Three species of other carnivores (mongooses, coyotes, and bobcats accounted for 92% of the cases reported among other carnivorous mammals. The most frequently reported rabid wildlife cases occurred in raccoons, skunks, bats, and foxes.1o The relative contributions of those species continue to change in recent decades because of fluctuations in enzootics of rabies among animals infected with several distinct variants of the rabies virus. During the past 30 years, rabies in domestic animals has steadily decreased in the United States, whereas annual occurrence in wild animals has increased. Wild animals accounted for 92% of all reported cases of rabies in 1995, a decrease from 1994. Raccoons were the most frequently reported rabid animal (50.3% of all animal cases), followed by skunks (22.5 %), bats (10.0 %), foxes (6.5%) and other wild animals, including rodents and lagomorphs (2.7%). Domestic animals accounted for nearly 8% of all rabid animals in the United States in 1995 . In recent years, the number of rabid cattle was equal to, or greater than, the number of rabid dogs. The incidence of rabies in horses is 'low compared to wildlife or domestic small animals but some yearly fluctuations occur. " tn 1990, for the first time since surveillance began in 1950, the number of cases in raccoons exceeded that in skunks. Raccoon rabies spread from Florida to raccoons in Georgia, Alabama, South Carolina, and North Carolina by natural spread.2 A separate focus in the northeastern States was caused by a translocation of raccoons from Florida, with legal permits to Virginia for restocking of hunting preserves.2 From the index case in a raccoon in 1977, near the Virginia-West Virginia border, over the next 17 years, 20 000 cases of rabies were recorded in raccoons, and several thousand associated cases in domestic dogs and other animals. In Canada, the rabies virus isolates from rabies-positive raccoons from 1982 to 1994 were the same strains found in foxes and skunks in eastern Canada,s and is different from the 'MidAtlantic' strain found in raccoons in the eastern United States. Local dynamics of epidemics of rabies in raccoons in the United States can be predicted.16 Historically, in North America, the number of cases of rabies in skunks exceeded that in either raccoons or foxes. Endemic skunk rabies occurs mainly in four geographical regions: southern Ontario and Quebec and upper New York State; the north central United States and the Canadian provinces of Manitoba, Saskatchewan, and Alberta; California; and south central United States. Within these broad areas, the disease persists in enzootic foci and erupts every 6-8 years. Experimental studies suggest that the species specificity of endemic rabies is due to differences in the pathogenicity of variants of rabies virus. Skunk rabies peaks in the spring and early winter, which is probably a reflection of certain life history events within the skunk population. The prevalence of rabies in bats in the United States is about 6%, and transmission to humans is rare even though sensational journalism has caused many people to consider bats as a serious threat to health. All of the confirmed cases of rabies in bats in Michigan in 1993 were associated with the big brown bat; in New York the prevalence in 1993 was 4.6% and nearly 90% of rabid bats were the common big brown bat. However, the silverhaired bat was associated with two human cases of rabies. Trends in national surveillance for rabies among bats in the United States from 1993 to 2000 have consistently found a diffuse geographic pattern of rabies in bats throughout the continental United StatesY Although spillover infection of bat variants of rabies among terrestrial animals such as dogs and cats are rare, these variants of rabies virus have been associated with 92% of the indigenously acquired human rabies infections in the United States since 1990Y Data from 37 states from 1993 to 2000 indicate an increased risk of rabies among certain groups of bat species was consistently found across season and most geographic regions of the USY The Brazilian free-tailed, eastern pipistrelle, and the silver-haired bats, when considered as a single group, were more rabid more frequently than were other bat gro.ups. All warm-blooded animals, with the possible exception of opossums, are susceptible, and there is no variation in susceptibility with age; 1-day-old pigs have been affected. Variation in susceptibility between species is noticeable. Foxes, cotton rats, and coyotes are extremely susceptible; cattle, rabbits, and cats are highly susceptible; dogs, sheep, and goats are moderately susceptible; and opossums little if at all. Distribution of virus variants The Lyssavirus genus belongs to the Rhadoviridae family of the Mononegavirales order and includes unsegmented RNA viruses causing rabies encephalomyelitis. They are well fitted to vectors belonging to the orders Carnivora (flesh-eating mammals including skunks), and Chiroptera (the order which comprises all of the 178 genera in 16 families of bats) . Seven genotypes have so far been delineated within the genus. These genotypes are divided into two immunopathologically and genetically distinct phylogroups. Phylogroup I includes two African genotyp es: Mokola virus, which has been isolated from shrews and cats, although its reservoir remains unknown, and Lagos bat virus, which has been found mainly in frugivorous bats but also in an insectivorous bat. Phylogroup II has five genotypes: Duvenhage virus (Africa), European bat lyssavirus I (EBLV-l; Europe), EBLV-2 (Europe), Aus tralian bat lyssavirus (Australia), and the classical Rabies virus (RABV, worldwide) . Members of the genotypes Duvenhage virus, EBLV- 1, and EBLV-2 are exclusively found in insectivorous bats, members of the genotype Australian bat lyssavirus are found in both insectivorous and frugivrorous bats, and member of the genotype RABV are found in carnivorous and American bats (insectivorous, frugivorous, and hematophagus) . The fact that lyssaviruses are well established in two ecologically distinct mammal orders may very likely be the consequence of successful host switching. . Analysis of 36 carnivoran and 17 chiropteran lyssavirus representing the main genotypes and variants strongly supports the hypothesiS that host switching occurred in the history of the lyssaviruses. In fact, lyssaviruses evolved in chiroptera long before the emergence of carnivoran rabies, very likely follOwing spillovers from bats.IS Using dated isolates, the emergence of carnivoran rabies from chiropteran lyssaviruses is estimated to have occurred 888 to 1459 years ago. In Europe, bat rabies is associated with two specific virus strains: European bat lyssavirus type 1 and European bat lyssavirus type 2. European bat lyssavirus type 1 isolates have been found in serotine bats in France.19 European bat lyssavirus type 2 virus have now been found in Daubenton's bats in England and Scotland.20 In North America, variants of rabies virus are maintained in the wild by several terrestrial carnivore species, including raccoons, skunks, and a number of bat species.21 Each antigenically and genetically distinct variant of the virus in mammalian species occurs in geographically discrete areas and is strongly associated with its reservoir species l1 Within each area, a spillover of rabies into other species occurs, especially during epidemics. Temporal and spatial analysis of skunk and raccoon rabies in the eastern United States, indicated that epidemics in raccoons and skunks moved in a similar direction from 1990 to 2000. However, to date there is no evidence that the raccoon rabies virus variant is cycling independently in the skunk population of the eastern United States or that the variant has undergone any genetic adaptations among skunks.21 Within broad geographic regions, rabies infections in terrestrial mammals can be linked to distinct virus variants, identified by panels of monoclonal antibodies or by genetic analysis.2 These analyses have demonstrated substantial differences between isolates from various parts of the world. Most outbreaks of rabies tend to be host species-specific. Each variant is maintained primarily by intraspecific transmission within a dominant reservoir, although spillover infection of other species may occur within the region. Geographic boundaries of the currently recognized reservoirs for rabies in terrestrial mammals have been established. Reservoirs for rabies virus are found worldwide. The virus is maintained at endemic and epidemic levels in a wide variety of Carnivora and Microchiroptera (bats) species. There are also antigenically similar rabies-like viruses, including the Makola . virus, the Lagos bat virus, Duvenhage virus, European bat lyssavirus 1 and European bat lyssavirus 2 rabies, which are found principally in small mammals (rodents, insectivores, insectivorous or frugivorous bats) . These strains appear to be limited in their geographical distribution to regions in Africa, unlike rabies virus which is distributed worldwide. The rabies-related viruses represent potential public and veterinary threats because of the lack of effective vaccines and the difficulties with diagnosis. The geographic boundaries of the currently recognized reservoirs for rabies in terrestrial species in North America are as follows: o Raccoons in the southeastern United States o Red and arctic foxes in Alaska, resulting in spread across Canada as far east as Ontario, Quebec, and the New England states Striped skunks in California, the north central States, and the south central States o Gray foxes in small reservoirs in Arizona o Coyotes in south Texas as a result of spread from domestic dogs in a longstanding reservoir at the Texas-Mexico border. The first reported occurrence of rabies in a human being infected with the raccoon rabies virus was from Virginia in 2002.14 In Ontario, wildlife rabies persists in two predominant species: the red fox and the striped skunk. Molecular epidemiology studies indicate that there is no host specificity, but rather there are very clear and consistent differences in the virus from distinct geographical regions. Such analyses will allow further epidemiological study of the behavior of the virus in different regions. Overlying the disease in terrestrial mammals are multiple, independent reservoirs for rabies in several species of insectivorous bats. Distinct viral variants can be identified for different bat species, but geographical boundaries cannot be defined for rabies outbreaks in the highly mobile bat species. Certain antigenic variants exist in nature against which conventional vaccines do not fully protect. In Canadian studies, two major antigenic groups can be distinguished among the rabies virus isolates examined. One group is found in Ontario, Quebec and the Northwest Territories and is represented in the wild by endemic red fox and striped skunk rabies that originated in northern Canada. The second group is found in Manitoba where striped skunk rabies is endemic. The epidemiology of rabies in Chile and the animal species which serve as rabies reservoirs have been examined.22 None of Chilean isolates segregated with viruses from the terrestrial reservoirs. No non-rabies lyssaviruses were found, and the Chilean samples were not related to viruses of the sylvatic cycle maintained by the common vampire bat. The Brazilian free-tailed bat was identified as the reservoir for the rabies genetic variant most frequently isolated in Chile from 1977 to 1998. The close association of a group of rabies viruses obtained from a domestic dog, Brazilian free-tailed bats, and a red bat with viruses maintained by red bat species in North America implicated species of this genus as the possible reservoirs of this particular genetic variant in Chile. In Trinidad, bovine rabies is common and is due to the bat type.23 Methods of transmission The source of infection is always an infected animal, and the method of spread is almost always by the bite of an infected animal, although contamination of skin wounds by fresh saliva may result in infection. Not all bites from rabid animals result in infection because the virus is not always present in the saliva and may not gain entrance to the wound if the saliva is wiped from the teeth by clothing or the coat of the animal. The virus may appear in the milk of affected animals, but spread by this means is unlikely as infection. The rabies virus is relatively fragile, susceptible to most standard disinfectants, and dies in dried saliva in a few hours. One of the most important parameters in rabies models is the transmission rate, or the number of susceptible animals infected by a diseased animal per unit of time. In a population of 19 raccoons feeding at a concentrated, common food source available during the summer in rural eastern Ontario, raccoons bite and are bitten an average of 0.99 to 1.28 times per hour, respectively. 24 Because of the natural occurrence of rabies in animals in caves inhabited by infected insectivorous bats, inhalation as a route of infection came under suspicion. It is now accepted that interbat spread, and spread from bats to other species is principally by bites, but that infection by inhalation also occurs. That infection can occur by ingestion has been put to use in devising systems of vaccinating wildlife by baiting them with virus-laden baits. This also has implications for epidemiological study generally. For example, attenuated viruses used in baits could be taken by . other than the target species, thus creating an unexpected seropositive segment of the animal population. It is also considered likely that outbreaks occurring naturally amongst carnivores may originate by them eating bats that have died of rabies. Animal vectors Traditionally, the dog, and to a minor extent the cat, have been the main source animals. However, native fauna, including foxes, skunks, wolves, coyotes, vampire, insectivorous and fruit-eating bats, raccoons, mongoose, and squirrels provide the major source of infection in countries where domestic carnivora are wellcontrolled. In general, foxes are less dangerous than dogs, foxes tending to bite only one or two animals in a group, while dogs will often bite a large proportion of a herd or flock. Raccoons and skunks are major reservoir of rabies in North America. Bats are the important species in which subclinical carriers occur. Multiplication of the virus without invasion of the nervous system is known to occur in fatty tissues in bats, and may be the basis of the 'reservoiring' mechanism in this species. Violent behavior is rare in rabid animals of this species, but has been observed. Bats represent a serious threat of spread of rabies because of their migratory habits. Most spread is within the species, but the threat to humans and animal species by bats cannot be completely disregarded. Although rodents can be infected with the rabies virus they are not thought to play any part in the epidemiology of rabies, either as multipliers or simply as physical carriers of the virus. Many of the viruses they carry are rabieslike rather than classical rabies. Rabies has occurred in swine herds where the skunk population is high, where farms were settled from rough terrain resulting in considerable interface between wildlife and domestic animals, and in which the management system allows the pigs to run free on the premises. The disease has occurred in pigs reared in a closed feeder barn where access by wildlife was very unlikely. There is a difference in role between vectors. For example, in Europe it is thought that foxes carry the infection into a new area, but other species disseminate it within an area.25 Foxes are the principal vectors and, as in Canada, cattle are the principal receptors. In western Canada, the main reservoirs of infection are skunks, bats, and foxes. This would have important consequences for control programs based on wildlife surveillance. Domestic livestock like cattle are rarely a source of infection, although chance transmission to humans may occur i f the mouth of a rabid animal is manipulated during treatment or examination. The virus may be present in the saliva for periods up to 5 days before signs are evident. Sea��onal spread Spread of the disease is often seasonal, with the highest incidence in the late summer and autumn because of largescale movements of wild animals at mating time and in pursuit of food. In Canada, th e frequency of rabies infection in livestock populations increases in the fall when adolescent foxes mature, begin mating behavior, and travel over large areas. Latent infection Because of rapid developments in virological techniques, especially serological screening of animal populations to obtain presumptive diagnoses of the presence of a virus in the population, the question of latent infection and inapparent carriers of rabies has assumed some importance. The presence of rabies antibodies in animals in a supposed rabies-free area is likely to arouse concern. Inapparent carriers do occur in bats and there is some evidence that latent infections can occur in other species. Zoonotic i m p l i cations The prime importance of rabies is its transmissibility to humans, with veterinarians being at special risk. European data indicate that by far the greatest proportion of humans requiring pretreatment for rabies have been exposed to a rabid domestic animal, not a wild one.I,3 Human rabies is extremely rare in countries where canine rabies is controlled by regular vaccination. In the United States, a total of 28 cases of human rabies occurred from 1980 to 1995. Most were due to viral variants associated with bats. Rates of post-exposure prophyl axis in developing countries are about 10 times higher than those in the United States, and rates of human rabies are approximately 100 times higher. According to the WHO, over 30 000 people die each year from rabies and more than 10 million undergo post- exposure treatment, having been bitten by a rapid anima1.3 In 1987, according to surveillance conducted by the World Health Organization, dogs were responsible for 91 % of all human rabies cases; cats, 2%; other domestic animals, 3%; bats, 2%; foxes, 1 %; and all other wild animals, fewer than 1 % . The disease is a major occupational hazard for veterinarians who should receive pre-exposure prophylaxis. Because horses will bite each other and their handlers, rabid horses that are aggressive pose a serious threat to humans. There is a lack of general rabies knowledge among the public 26 The laissez-faire attitude toward rabies by Americans causes instances of rabies exposure to be commonplace. A survey of middle school children in Texas found a lack of basic knowledge about rabies. Only 0.3% of children achieved a minimum score of 75% on a survey of knowledge about rabies.26 Respondents lacked knowledge about the disease is transmitted, and less than one-third were even aware of rabies epidemic in southern Texas despite the fact that a rabies epidemic had been occurring in southern Texas for the previous 13 years. Even more astonishing was the finding that 80% knew of the risk of acquiring rabies from an unvaccinated pet buy 57% claimed to own unvaccinated pets. Rabies is not of major economic importance in farm animals, although individual herds and flocks may suffer many fatalities. The disease in human has always been considered fatal. Since 1970, there have been reports of five patients said to have survived rabies encephalitis.4 All patients had received some rabies vaccine before the onset of clinical signs but none had had rabies immunoglobulin. A 15-year-old girl who developed rabies one month after being bitten by a bat survived following intensive medical therapy including induced coma while a native immune response matured, and treatment with ketamine, midazolam, ribarvirin, and amantadine.27 Probable drug-related toxic effects included hemolysis, pancreatitis, acidosis, and hepatotoxicity. The patient was discharged to her home after 76 days, and at nearly ! 5 months after her initial hospitalization she was alert and communicative, but with choreoathetosis, dysarthria, and an unsteady gait. Rabies in the Americas. Between 1993 and 2002, the number of human Jnd canine rabies cases in the Americas Region fell by approximately 80% .28 There were 39 human cases in 2002, 63% of them transmitted by dogs. Human rabies transmitted by wildlife, mostly by bats is a risk to inhabitants in many countries in the Region. This sharp reduction is attributable mainly to the control measures implemented by the countries in the Region, such as mass vaccination of dogs and prophylactic treatment of people who have been exposed. Econom ic importance ! The economic costs of rabies in a country . are associated with pet animal vaccinations, animal bite investigations, confinement and quarantine of domestic animals which bite humans or which are suspected of exposure to rabid animals, salaries of animal control officers, laboratory diagnosis, the costs of pre-exposure and post-exposure prophylaxis and treatment and consultation, public education, staff training and clerical costs. The cost of the 'point infection control' program as a response to raccoon rabies introduction in Ontario in 1999 was $363 000 (Cdn) or $500 Cdn/km2. The costs were justified as by containing the spread of raccoon rabies, annual savings to Ontario are estimated at $8 to 12 million.29 The reported associated costs in Ontario before raccoon rabies occurred were estimated at about $6 million annually, excluding pet vaccination costs. PATHOGENESIS Following the deep introduction of rabies virus by the bite of a rabid animal, initial virus multiplication occurs in striated muscle cells at the site. The neuromuscular spindles then provide an important site of virus entry into the nervous system. Entry into the nervous system may also occur at motor end plates. In the olfactory end organ in the nares, neuroepithelial cells are in direct contact with the body surface and these cells extend without interruption into the olfactory bulb of the brain. Following entry of the virus into nerve findings, there is invasion of the brain by passive movement of the virus within axons, first into the spinal cord then into the brain1,4 The immune response during this phase of the infection is minimal and explains why neutralizing antibody and inflammatory infiltration are usually absent at the time of onset of encephalitic signs. Antibody titers reach substantial levels only in the terminal stages of the disease. Following entry of rabies virus to the central nervous system (CNS), usually in the spinal cord, an ascending wave of neuronal infection and neuronal dysfunction occurs. The primary lesions produced are in the CNS, and spread from the site of infection occurs only by way of the peripheral nerves. This method of spread accounts for the extremely variable incubation period, which varies to a large extent with the site of the bite. Bites on the head usually result in a shorter incubation period than bites on the extremities. The severity and the site of the lesions will govern to a large extent whether the clinical picture is primarily one of irritative or paralytic phenomena. The two extremes of the paralytic or dumb form and the furious form are accompanied by many cases that lie somewhere between the two. Gradually ascending paralysis of the hindquarters may be followed by severe signs of mania, which persist almost until death. Destruction of spinal neurons results in paralysis, but when the virus invades the brain, irritation of higher centers produces manias, excitement, and convulsions. Death is usually due to respiratory paralysis. The clinical signs of salivation, indigestion and pica, paralysis of bladder and anus, and increased libido all suggest involvement of the autonomic nervous system, including endocrine glands. At death, there are viral inclusions and particles in almost all neurons in the brain, spinal cord and ganglia, but none in the supportive cells of the CNS. Electron microscopic examination also shows the presence of the virus in the cornea, which it reaches centrifugally along the peripheral nerves. Virus reaches the salivary glands and many other organs in the same way, but the highly infective nature of saliva arises from passage of the virus along the olfactory nerve to taste buds and other sensory end organs in the oropharynx, rather than from the salivary glands. Experimentally, infection of non -nervous tissues in skunks and foxes has been reproduced in the adrenal medulla, cornea, and nasal glands.19 The virus may be found in milk, in some organs and in fetuses, but the virus cannot be demonstrated in the blood at any time. Variations in the major manifestations as mania or paralYSis may depend upon the source of the virus. Virus from vampire bats almost always causes the paralytic form. 'fixed' virus that has been modified by serial intracerebral passage causes ascending paralysis in contrast to 'street' virus, which more commonly causes the furious form. The site of infection and the size of the inoculum may also influence the clinical course. There is also geographical difference in the proportion of animals affected by the furious or paralytic form of the disease. In the Americas most cases are paralytic. In Africa and India most cases in farm animals are the furious form. The disease is always fatal, but infrequently an experimentally infected animal shows clinical signs of the disease but recovers. There are two recent records of spontaneous recovery in man, and the occurrence of non-fatal rabies in all species has been reviewed. There appears to be no field occurrence in domestic animals of the finding in experimentally infected mice that some strains of virus invade only peripheral nerves and spinal ganglia leaving a number of survivors With permanent nervous disability. The pathogenesis of recovery from rabies is important relative to vaccination and serological testing to determine the incidence and prevalence of the disease. The literature on the animal models used for the study of the pathogenesis and treatment of rabies has been reviewed.1 CLINICAL FINDINGS Cattle and sheep Cattle Among farm animals, cattle are most commonly affected. The incubation period in naturally occurring cases is about 3 weeks, but varies from 2 weeks to several months in most species, although incubation periods of 5 and 6 months have been observed in cattle and dogs. In one large -scale outbreak in sheep, deaths occurred 17-1 11 days after exposure. Experimentally, in cattle the average incubation period was 15 days and the average course of the disease was 3.7 days. Unvaccinated cattle had shorter incubation and clinical duration of disease than vaccinated cattle. Major clinical findings included excessive salivation (100%), behavioral change (100%), muzzle tremors (80%), vocalization (bellowing 70%), aggression, hyperesthesia and/or hyperexcitability (70 %), and pharyngeal paralysis (60 %). The furious form occurred in 70% . In sheep, experimentally, the average incubation period was 10 days, and the average course of the disease was 3.25 days. Major clinical findings included muzzle and head tremors (80%), aggressiveness, hypereXCitability and hyperesthesia (80%), trismus (60%), salivation (60%), vocalization (60%), and recumbency (40%). The furious form occurred in 80% of sheep. In the paralytic form, knuckling of the hind fetlocks, sagging and swaying of the hindquarters while walking, often deviation or flaccidity of the tail to one side, are common early signs. Decreased sensation usually accompanies this weakness and is one of the best diagnostic criteria in the detection of rabies. It is most evident over the hindquarters. Tenesmus, with paralysiS of the anus, resulting in the sucking in and blOwing out of air, usually occurs late in the incoordination stages just before the animal becomes recumbent. This is a characteristic finding but it may be transient or absent. Drooling of saliva is one of the most constant findings. The yawning movements are more accurately described as voiceless attempts to bellow. When paralysis occurs, the animal becomes recumbent and unable to rise. Bulls in this stage often have paralysiS of the peniS. Death usually occurs 48 hours after recumbency develops and after a total course of 6-7 days. The paralytic form of rabies has been reproduced experimentally by the 1M injection of brain tissue from naturally occurring cases of paralytic rabies (' derriengue') in cattle in Mexico. In furious rabies the animal has a tense, alert appearance, is hypersensitive to sounds and movement, and is attracted to noise so that it may look intently or approach as though about to attack. In some cases, it will violently attack other animals or inanimate objects. The'se attacks are often badly directed and are impeded by the incoordination of gait. Frequently, loud bellowing is usual at this stage. The sound is characteristically hoarse and the actions are exaggerated. Sexual excitement is also common, bulls often attempting to mount inanimate objects. Multiple collections of semen for artificial insemination have been made during very short periods from bulls that later proved to be rabid. With this violent form of the disease the termination is characteristically sudden. Severe signs may be evident for 24-48 hours and the animal then collapses suddenly in a paralyzed state, dying usually within a few hours. There is no consistent pattern in either the development or the range of signs. Body temperatures are usually normal but may be elevated to 39.5-40.soC (103-105°F) in the early stages by muscular activity. Appetite varies also. Some animals do not eat or drink, although they may take food into the mouth. There is apparent inability to swallow. Others eat normally until the terminal stages. The course may vary from 1 to 6 days. So wide is the variation in clinical findings that any animal known to be exposed and showing signs of spinal cord or brain involvement should be considered rabid until proved otherwise. Sheep In sheep, rabies often occurs in a number of animals at one time due to the ease with which a number of sheep can be bitten by a dog or fox. Clinically, the picture is similar to that seen in cattle. The minority show sexual excitement, attacking humans or each other, and vigorous wool pulling; sudden falling after violent exertion, muscle tremor, and salivation are characteristic. Excessive bleating does not occur. Most sheep are quiet and anorectic. Goats are commonly aggressive, and continuous bleating is common. Horses Most recorded cases in horses are lacking in distinctive nervous signs initially, but incline to the paralytic form of the disease. Experimentally, the average incubation period was 12 days and the average duration of disease was 5.5 days.30 Unvaccinated animals had shorter incubation periods and duration of clinical disease. Muzzle tremors were the most frequently observed and most common initial signs. Other clinical findings included pharyngeal paresis (71 %), ataxia or paresis (71 %), and lethargy or somnolence (71 %). The furious form occurred in 43% of cases, some of which began as the dumb form. The paralytic fo..r m was not observed. I�� naturally occurring cases, the initial clinical findings may include abnormal postures, frequent whinnying, unexplained aggressiveness and kicking, biting, colic, sudden onset of lameness in one limb followed by recumbency the next day, high-stepping gait, ataxia, apparent blindness, and violent head- tossing. Lameness or weakness in one leg may be the first sign observed, but the usual pattern of development starts with lassitude, then passes to sternal recumbency and lateral recumbency, followed by paddling convulsions and terminal paralysis. In a series of 21 confirmed cases in horses, the clinical findings at the time of initial examination included ataxia and paresis of the hindquarters (43%), lameness (24%), recumbency (14%), pharyngeal paralysis (10%), and colic (10%) .31 The major clinical findings observed over the course of hospitalization included recumbency (100%), hyperesthesia (81%), loss of tail and anal sphincter tone (57%), fever -38.5°C (52%), and ataxia and paresis of the hindquarters (52%). Mean survival time after the onset of clinical signs was 4.47 days (range, 1-7 days) . Clinical findings of the furious form of rabies, such as aggressiveness (biting), compulsive circling, and abnormal vocalization, were evident in only two horses. Supportive therapy, given to nine horses, had no effect on survival time and did not correlate with the detection of Negri bodies at necropsy. Horses developing the furious form show excitement, become vicious, and bite and kick. Their uncontrolled actions are often violent and dangerous and include blind changes, sudden falling and rolling and chewing of foreign material or their own skin. Hyperesthesia and muscular twitching of the hindlimbs followed by crouching and weakness are also recorded in the horse. Pigs Pigs manifest excitement and a tendency to attack, or dullness and incoordination. Affected sows show twitching of the nose, rapid chewing movements, excessive salivation, and clonic convulsions. They may walk backward. Terminally, there is p aralysis and death occurs 12-48 hours after the onset of signs. The clinical findings in pigs are extremely variable, and individual cases may present in a variety of ways and only one or two of the classical findings may occur. CLINI CAL PATHOLOGY No antemortem laboratory examination is of diagnostic value, but tests for lead on blood, urine, and feces may help to eliminate lead poisoning as a possible diagnosis. Virus neutralization tests are available, but the presence of antibodies is not diagnostic. Other available tests are passive hemagglutination, complement fixation, radioimmunoassay, and indirect fluorescent antibody staining. These are used to determine immune status rather than as a diagnostic aid. An ELISA is available for measurement of rabiesspecific antibody in the sera of major domestic and wildlife reservoirs in North America. N ECROPSY FINDINGS Confirmation of a diagnosis of rabies depends on careful laboratory examination of fresh brain. The recommended laboratory procedure includes the following three tests and it is recommended that at least two of them be used on all specimens. o A fluorescent antibody test (FAT) on impression smears from the brain - current recommendations include sampling of the hippocampus, medulla oblongata, cerebellum or gasserian ganglion. However, a recent publication stipulates that the hippocampus and cerebellum are less desirable samples than the thalamus, pons, or medulla for the detection of viral antigen, and that the current sampling recommendations stem from the visibility of Negri bodies, rather than the true distribution of viral antigen 32 An FAT can be completed in approximately 2 hours and is highly accurate when done routinely by experienced personnel. The reliability of FAT confirmed by the mouse inoculation test is over 99 % .14 Those specimens that are negative on FAT, and have contact with humans, are inoculated into experimental mice. The incubation period in mice before clinical signs are seen averages 11-12 days (range of 4-18 days), and death occurs in 7-21 days. The mouse brain is harvested as soon as signs appear and is submitted to the same tests described above. Thus a positive result can be obtained as soon as 4-7 days after inoculation. Some mice must be left for the full 21 days because only a negative result at that time can give a complete negative to the test. A tissue culture infection test is now available, which allows demonstration of the virus in stained tissue culture cells within 4 days. This may replace the mouse inoculation test 9 A dot ELISA is available for the detection of rabies antigen in animals 33 It is rapid, simple, economical and, in comparison with the FAT, the agreement is 95 %. A histological search for Negri bodies in tissue sections with results available in 48 hours. Because of false-positive diagnoses the technique is in some disrepute. An immunoperoxidase test for rabies can be used on formalin-fixed, p araffin-embedded brain tissues of domestic animals and wild animals when fresh tissues are not available.16,23 In some cases, the brain tissue may be negative for the rabies virus using standard diagnostic techniques but immunohistochemical tests may detect the presence of antigen.20 A reverse transcriptase polymerase chain reaction test has been found of value in detecting rabies infection in decomposed brain samples that were negative by the direct fluorescent antibody test.34 The histopathologic changes of rabies infection include a non -suppurative encephalomyelitis and ganglioneuritis, with neuronal necrosis and the formation of glial nodules. Negri bodies are most commonly found in the Purkinje cells of the cerebellum irl ruminants. Spongiform change has also been reported in the brain of a heifer irlfected with rabies viruS 35 Samples for confirmation of diag nosis o Histology - one half of midsagittallysectioned brain, cervical spinal cord (including root ganglia), gasserian ganglion, parotid salivary gland (LM, IHC) o Virology - one half of midsagittallysectioned brain, cervical spinal cord (FAT, ISO, BIOASSAy) . Note the zoonotic potential of this organism when handling carcass and submitting specimens. DIFFERENTIAL DIAGNOSIS The diagnosis of rabies is one of the most difficult and important duties that a veterinarian is called upon to perform. Since in most cases there. is a probability of h u ma n exposure, .failure to recognize the disease may place human life in jeopardy. It is not even sufficient to say that if rabies . occurs in the area one will classify every animal showing nervous signs as rabid, because nervous signs may not be evident for some days after the illness commences. In addition, many animals suffering from other diseases will be left u ntreated. The best pol icy is to handle all suspect animals with extreme care but continue to treat them for other diseases if such treatment appears to be indicated. If the animal is rabid, it will die and the diagnosis can then be confirmed by laboratory examination Several di,Seases ar�� characterized by signs of abnormal mental state or paralysis, or a combination bf,both (see Table 22.1 for the horse; Table 32.3 for cattle): Rabies must be differentiated from the following common diseases affecting the nervous '''system, accordirig to species: Cattle and sheep • Lead poisoning, In acute and subacute lead poisoning in cattle the clinical findings are similar to those of furious and dumb rabies. In acute lead poisoning, the common clinical findings are blindness, convulsions, champing of the jaws with the production of frothy saliva, and twitching of the eyelids and ears. In subacute lead poisoning in cattle there is blindriess, stupor, headpressing, grinding of the teeth, and almost no response to treatment. Rabid cattle are usually not blind, and signs of motor irritation such as convulsions and twitching of the facial muscles usually do not occur. However, there are signs of bizarre mental behavior, such as wild gazing, bellowing, yawning, attacking, and compulsive walking • Lactation tetany occurs in lactating cattle on lush pasture in the spring during cold wet and windy weather, and is characterized by hyperesthesia, tremors, convulsions, recumbency, and rapid death • Vitamin A deficiency occurs in groups of young cattle from 6 months to 1 8 months of age not receiving adequate carotene intake or vitamin A supplementation and is characterized by blindness in the ocular form and episodes of tremors and convulsions • Polioencephalomalacia in cattle and sheep is characterized by blindness, nystagmus, opisthotonos, and convulsions; bellowing, loss of sensation, and tenesmus do not occur • Listeriosis in cattle and sheep is man ifested by localizing signs of circling and facial nerve paralysis • Enterotoxemia in sheep is usually confined to lambs on heavy carbohydrate d iets • Pregnancy toxemia is a disease of pregnant ewes and is readily differentiated by the presence of ketonuria • Louping-ill in sheep is transmitted by insects, has a seasonal occurrence, and a localized geographical distribution. Pigs In pigs, rabies must be differentiated from pseudorabies, Teschen's disease, and involvement of the brain in several other diseases of the pigs, such as hog and African swine fever, meningitis associated with Streptococcus suis type II, Haemophilus spp., Glasser's disease, Escherichia coli, septicemia, and erysipelas. Horses In horses, rabies must be differentiated from several diseases of the nervous system (summarized in Table 22). The most common include: viral encephalomyelitis, herpes virus myeloencephalopathy, cerebrospinal nematodiasis, equine degenerative myeloencephalopathy, equine protozoal myeloencephalitis, neuritis of the cauda equina, horsetail poisoning, Borna, Japanese encephalitis, botulism . TREATMENT No treatment should be attempted after clinical signs are evident. If the bite is seen, immediately after exposure, irrigation of the wound with 20% soft soap solution or a solution of Zephiran may prevent the establishment of the infection. Immediate and thorough washing of all bite wounds and scratches with soap and water is perhaps the most effective measure for preventing rabies in veterinarians bitten by rabid animals. In experimental animals, simple local wound cleansing has been shown to markedly reduce the likelihood of rabies. Post-exposure vaccination is unlikely to be of value in animals, as death usually occurs before appreciable immunity has had time to develop. Euthanasia of suspect animals must be avoided, particularly if human exposure has occurred, since the development of the disease in the animals is necessary to establish a diagnosis. Antirabies semm may become available for animal treatment at some future date. In some countries, cases of rab ies in farm animals are notifiable to the animal health and disease regulatory bodies. CONTROL The major goal of rabies control in domestic and wild animals is the reduction or elimination of human rabies. The most rational approach to reducing human rabies is to reduce the prevalence and incidence of disease in animals. In developed countries, this has been accomplished by vaccination of dogs and cats, leaving much rabies in wildlife to be controlled. In countries without wildlife reservoirs, such as the Philippines, it would be economically advantageous to eliminate dog rabies. In Africa, where the incidence of rabies as well as the range of species involved is increasing, there is a need to develop new and economical methods of vaccinating domestic animals. Pre-exposure immunization for individuals, like veterinarians, who are at high risk to rabies, has been recommended by the World Health Organization, since it reduces risk and provides a more rapid anamnestic response, eliminating the need for human globulin should exposure occur. Rabies pre- exposure vaccination is now mandatory in many veterinary colleges. Despite some mild adverse reactions, immunization against rabies is an important prophylaxis measure wellaccepted by veterinary students. For farm animals, there are two useful control techniques: the prevention of exposure and pre-exposure vaccination. Prevention of exposure to the virus This can be achieved by controlling access of wildlife species which are likely to come into contact with the farm livestock in particular areas or through vaccinatiqn of the wildlife. Foxes accounted for a very large proportion (85% in Europe) of wildlife rabies, and a control program aimed at reducing their population using poison or traps was attempted until the 1970s 36 This method of population reduction failed to control outbreaks or reduce enzootic rabies. Point infection control. To control the introduction of raccoon rabies in Ontario in 1999, 'point infection control' was used to control the epidemic.29 This involves the use of three tactics: population reduction, trap-vaccinate-release, and oral vaccination with baits to control the spread of raccoon rabies. Some raccoons were captured and euthanized which resulted in an 83 to 91 % reduction in the raccoon population in an area of 225 km2 around the location of the three original cases of raccoon rabies . Raccoon denSity in the population reduction zones declined from 5.1 to 7.1 km2 to 0.6 to 1.1 km2 follOwing control. Cats were also captured, vaccinated and released. Raboral V-RG oral rabies vaccine was distributed aerially to vaccinate free ranging raccoons. The point infection control program is considered to be highly successful and will continue to be used to contain isolated cases of raccoon rabies.29 Pre-exposure vaccination of hu mans The most successful form of rabies prevention is pre-exposure vaccination. In human medicine, there are no reported cases of rabies deaths in anyone who has had pre-exposure vaccination followed by a booster vaccination if exposed.4 The Centers for Disease Control (CDC) and Prevention has published the recommendations of the Advisory Committee on Immunization Practices (ACIP) for human rabies prevention, which indicate that rabies pre- exposure vaccination should be offered to persons more likely to be exposed to rabies vims than the population of the United States at large.37 The recommendations of the ACIP for pre-exposure prophylaxis and maintenance of a detectable antibody titer differ depending on the estimated degree of risk of exposure to the vims. Four risk categories have established: continuous; frequent; infrequent; and rare. The classification depends on factors such as the occupation of the individual and geography.38 With directed continuing education, common sense, first aid, and the availability of modem biological agents, human rabies is nearly always preventable .1 Rabies pre- exposure vaccination is recommended for anyone at increased risk of exposure to rabies, including veterinarians, veterinary students who work in uunivers it y veter inar y teach ing h os pitals, lab orat or y sta ff w ork ing with rab ies, vacci ne pr oducers, a nimal a nd w ildl ife c ontr ol pers onnel, a nd z ool og ists. Th e sta nda rd pre-ex pos ur e regime n is th ree d oses of vacc ine 1M or ID on da ys 0, 7, a nd 28 ( or 21). A b ooster d ose a fter 1 year increases a nd pr olongs the a ntib od y res ponse.4 Th is pre -ex pos ure vacci nat ion perm its post-ex pos ure vacc inati on t o c ons ist of tw o d oses of vacci ne on da ys 0, a nd 3 instead of 5 on da ys 0,3,7, 14, a nd 28 a nd av oids the need for post ex pos ure of adm inistrat ion of h uma n rab ies imm unogl ob uli n. A large proporti on of at-risk sta ff members w ork ing i n veter inar y cl inics, a nim al shelters, a nd w il dlife rehab ilitat ion ce nters in a st ud y area d id not rece ive rabies pre -ex pos ure vacc ni at ion acc ordi ng t o the rec omme ndati ons of the ACIP of the CDC.3 7,38 C ost ma y be fact or beca use ma ny of the se em pl oyees are c omm only sh ort-te nn, part-t ime, or v ol unteer w orkers. Post-exposure vaccination of humans Moder n post-ex pos ure treatme nt is highl y s uccess ful if d one adeq uate l y. Wound care w ith passive a nd act ive rab ies imm unizati on are es se nt ial es pec iall y after severe ex pos ure. P ost- ex pos ure treatme nt is ass umed t o ne utral ize or inact ivate virus wh ile it is st ill i n the w ounds, be fore it ga ins access t o the nerv ous s ystem where it is pr otected fr om t he imm une s ystem. There fore, treatme nt a fter ex pos ure t o rabies v ir us is ver y urge nt, eve n i f the pat ie nt was b itte n m onths be fore. Th or ough washi ng of rabies-i nfected w ounds with s oa p a nd wa ter ca n increase s urv iva l b y 50% 3 However, th is inex pe ns ive, readi ly ava ilab le treatme nt is om itted i n m ost cases. The World Health orga nizat ion rec omme nds a m ulti-site intradermal reg ime n of 0.1 mL of v acc ine at eight s ites on da y 0, at four sites on da y 7, a nd at one site each on da ys 28 a nd 90.39 Passive imm unizati on w ith h uma n rab ies imm unogl ob ul in lowers m ortalit y a fter severe ex pos ure. Post-exposure vaccination of domestic animals An e ffect ive post -ex pos ure pr ot oc ol for unvacc inated d omestic a nimals ex posed t o rab ies incl udes immed iate vacci nat ion agai nst rab ies , a str ict is olati on per iod of 90 da ys, a nd admi nistrat ion of b ooster vacc inat ions d uri ng the th ird a nd eighth weeks of the is olati on per iod .40 The pr ot oc ol has bee n e ffect ive in d ogs, cats, cattle, a nd h orses.4o Vaccination of domestic animals A Compendium of Animal Rabies Control is pub lished a nnua ll y b y the Nati onal Ass oc iati on of State P ub lic Health Veter inar ia ns, I nc. i n the United States a nd Ca nada.25 It pr ov ides rec omme ndati ons for imm unizati on pr oced ures in d omes tic a nimals , the vacci nes l ice nsed a nd marketed i n the United States. Detailed i nformat ion is pr ov ided on preex pos ure vacc inati on, ma nageme nt of d ogs a nd cats a nd l ivest ock, postex pos ure ma nageme nt, a nd c ontr ol meth ods i n wild a nimals. S uch publicati ons sh ould be c ons ulted whe n necessar y. I n ge neral, for cattle, shee p, a nd h orses the primar y vacci nati on is g ive n at 3 m onths of age a nd b oosters g ive n a nnuall y. Farm livest ock in e ndemic areas where cl inical cases of rab ies occ ur c omm onl y sh ould be vacc inated. In c ountr ies where vam pire bats are a maj or vect or for rab ies in farm l ivest ock, vacci nati on of l ivest ock is necessar y b ut in c ountr ies s uch as Arge nt ina, vacc inat ion d oes not s upport a c ost be ne fit a nal ysis Y Vaccines Alm ost al l rabies vacc ines for d omest ic a nimals are i nactivated.25 I nact ivated t si s ue c ult ure cell vacc ines g vi e n t oc attle res ult i n ne utraliz ing a nt ib od ies in 1 m onth a fter the pr imar y vacc inati on. A b ooster give n 1 year later i ncreases the titers, wh ich are detectable 1 year a fter the b ooster. A vacc ine inactivated with b inar y-eth yle nim ine, a nd c onta ini ng al umi num h ydr oxide adj uva nt, pr ov ides excelle nt pr otect ion for up t o3 years a nd is ver y useful for the c ontr ol of rab ies i n cattle in Lat in Amer ica where the vam pire bat is the mai n vect or. Vacci nal a nt ib od ies are prese nt in the c ol ostr um of vacci nated c ows a nd it is rec omme nded that, where cattle are vacc inated a nnuall y, calves be vacc inated at 4 m onths of age a nd aga in whe n 10 m onths of age. Calves fr om unvacc inated dams ca n be pr otected b y vacc inat ing them at 17 da ys of age. P ostvacci nal paral ysis d oes not occ ur a fter its use. A post -ex pos ure vacci nati on pr ot oc ol i ncl ud ing immediate rab ies vacci na ti on, w ith a mi nim um of one b ooster vacc inati on pr ior t o release fr om q uara nt ine, a nd 90 da ys strict is olat ion, was 99.7% s uccess ful i n unvacci nated catt le, h orses, shee p, g oats, a nd pigs. Vaccination of wildlife The litera ture on oral rabies vacc inat ion of vvild ca nliv ores i n the United States has bee n re viewed.42 Mas s ora l vacc inat ion of terrestr ial w ild a nim als is a rabies c ontr ol meth od that is feas ible, e ffective, a nd inte mat ionall y acce pted.36,42,43 It is based on the c once pt of a pplied herd imm unit y. T he vacci nes are e fficaci ous whe n fed as vacc ine-baits. The fact ors affect ni g acce pt a nce of baits for delivery of ora l rabies vacci ne t or acc oons have bee ne xami ned.44 The oral imm unizati on of foxes has res ulted in a s ubsta nt ial decrease in the number of rabies cases in E ur ope. As a res ult of oral vacc inat ion of the red fox (Vulpes vulpes) aga inst rab ies, us ing ha nd a nd aerial distr ib ut ion of vacc ine-lade n ba its, the rab ies vir us has a lm ost bee n ' c om plete ly erad icated fr om Wester n a nd Ce ntral E ur ope. 45 The same dramatic decrease oc curred i n s outher n Ontar io, Ca nada. In m ost c ountries, vacci ne ba its were d istr ib uted tw ice year ly; d ur ing the s pri ng ( March t o Ma y) a nd a ut um n (Se ptember t oO ct ober). Sever al E ur opea n c ountr ies have bec ome rab ies -free : Belgi um, Luxemb ourg, Fra nce, Ital y, Sw itzer land, f inla nd and the Netherla nds.43 With the E ur opea n Union c ons ist ing of 25 c ountr ei s from Ma y2 004,al l the sc ie nt ifci k nowledge is ava ilab le for establ ishi ng e ffic ie nt a nd ada pted oral vacci nat ion pr ograms a imed at el im inati ng terrestria l rabies fr om th is area. Pr ogress has bee n made i n a pplying oral rab ies vacc inat ion t o c onta in a nd e limi nate s ome strai ns of terrestr ial rab ies i n N orth Amer ica.42 N otable exam ples i nc lude near elimi nati on of rab ies fr om red foxes in s outher n Ontar io. C ontai nme nt a nd elim inat ion of ca nine rabies c oyotes fr om s outh Texas, c onta inme nt a nd near el im inat ion of racc oon rab ies fr om Oh io, preve nt ion of racc oon rabies s pread thr ough the Lake Cham pla in Valle y i n New York a nd acr oss northe m Verm ont a nd New Ham psh ire, a nd red uced inc ide nce of rab ies where other ora l rab ies vacci nati on pr ojects targeti ng racc oons have occ urred. As of 2005, b oth Ontar io a nd New Br unsw ick were free of racc oon rabies for greater tha n 10 m onths a nd 2 year s, res pectivel y, a fter im pleme ntat ion of'point infect ion c ontr ol 'strateg ies 29 b ut c onti nued s urve illa nce is crit ical t o m onit or e ffective ness. Rab ora IV -RG is the onl y rabies vacci ne lice nsed for use in the United States. It has not pr od uced s uffic ie nt levels of populat ion imm unit y i n sk unks i n the w ild at the c urre nt d ose a nd V-RG ma y be less e ffect ive in sk unks tha n other s pecies. Sk unks are a maj or c ontr ib ut or t or abie s in N orth fuller ica with 38% of cases ass ociate d w ith the racc oon varia nt of rabies virus inv olved sk unks i n 2001Y This has ra ised c onc er ns ab out a n inde pe nde nt ma inte na nce c yc le for racc oon rab ies i n sk unks. The nat ional rabies ma nageme nt g oals of v ir us c ontai nme nt a nd e limi nat ion of w li ll ki el y rema in e lus ive unt il a n oral vacc ine is l ice nsed that is imm unoge nic i n all terrestr ial rab ies reserv oir s pec ies. Sk unk rabies v ir us, wh ich has the br oadest ge og ra ph iC d istr ib ut ion of all terrestr ial rab ies va ria nts in the USA ca n c urre ntl y be addressed onl y thr ough l ocal trap vaccipub lished a nnua ll y b y the Nati onal Ass oc iati on of State P ub lic Health Veter inar ia ns, I nc. i n the United States a nd Ca nada.25 It pr ov ides rec omme ndati ons for imm unizati on pr oced ures in d omes tic a nimals , the vacci nes l ice nsed a nd marketed i n the United States. Detailed i nformat ion is pr ov ided on preex pos ure vacc inati on, ma nageme nt of d ogs a nd cats a nd l ivest ock, postex pos ure ma nageme nt, a nd c ontr ol meth ods i n wild a nimals. S uch publicati ons sh ould be c ons ulted whe n necessar y. I n ge neral, for cattle, shee p, a nd h orses the primar y vacci nati on is g ive n at 3 m onths of age a nd b oosters g ive n a nnuall y. Farm livest ock in e ndemic areas where cl inical cases of rab ies occ ur c omm onl y sh ould be vacc inated. In c ountr ies where vam pire bats are a maj or vect or for rab ies in farm l ivest ock, vacci nati on of l ivest ock is necessar y b ut in c ountr ies s uch as Arge nt ina, vacc inat ion d oes not s upport a c ost be ne fit a nal ysis Y Vaccines Alm ost al l rabies vacc ines for d omest ic a nimals are i nactivated.25 I nact ivated t si s ue c ult ure cell vacc ines g vi e n t oc attle res ult i n ne utraliz ing a nt ib od ies in 1 m onth a fter the pr imar y vacc inati on. A b ooster give n 1 year later i ncreases the titers, wh ich are detectable 1 year a fter the b ooster. A vacc ine inactivated with b inar y-eth yle nim ine, a nd c onta ini ng al umi num h ydr oxide adj uva nt, pr ov ides excelle nt pr otect ion for up t o3 years a nd is ver y useful for the c ontr ol of rab ies i n cattle in Lat in Amer ica where the vam pire bat is the mai n vect or. Vacci nal a nt ib od ies are prese nt in the c ol ostr um of vacci nated c ows a nd it is rec omme nded that, where cattle are vacc inated a nnuall y, calves be vacc inated at 4 m onths of age a nd aga in whe n 10 m onths of age. Calves fr om unvacc inated dams ca n be pr otected b y vacc inat ing them at 17 da ys of age. P ostvacci nal paral ysis d oes not occ ur a fter its use. A post -ex pos ure vacci nati on pr ot oc ol i ncl ud ing immediate rab ies vacci na ti on, w ith a mi nim um of one b ooster vacc inati on pr ior t o release fr om q uara nt ine, a nd 90 da ys strict is olat ion, was 99.7% s uccess ful i n unvacci nated catt le, h orses, shee p, g oats, a nd pigs. Vaccination of wildlife The litera ture on oral rabies vacc inat ion of vvild ca nliv ores i n the United States has bee n re viewed.42 Mas s ora l vacc inat ion of terrestr ial w ild a nim als is a rabies c ontr ol meth od that is feas ible, e ffective, a nd inte mat ionall y acce pted.36,42,43 It is based on the c once pt of a pplied herd imm unit y. T he vacci nes are e fficaci ous whe n fed as vacc ine-baits. The fact ors affect ni g acce pt a nce of baits for delivery of ora l rabies vacci ne t or acc oons have bee ne xami ned.44 The oral imm unizati on of foxes has res ulted in a s ubsta nt ial decrease in the number of rabies cases in E ur ope. As a res ult of oral vacc inat ion of the red fox (Vulpes vulpes) aga inst rab ies, us ing ha nd a nd aerial distr ib ut ion of vacc ine-lade n ba its, the rab ies vir us has a lm ost bee n ' c om plete ly erad icated fr om Wester n a nd Ce ntral E ur ope. 45 The same dramatic decrease oc curred i n s outher n Ontar io, Ca nada. In m ost c ountries, vacci ne ba its were d istr ib uted tw ice year ly; d ur ing the s pri ng ( March t o Ma y) a nd a ut um n (Se ptember t oO ct ober). Sever al E ur opea n c ountr ies have bec ome rab ies -free : Belgi um, Luxemb ourg, Fra nce, Ital y, Sw itzer land, f inla nd and the Netherla nds.43 With the E ur opea n Union c ons ist ing of 25 c ountr ei s from Ma y2 004,al l the sc ie nt ifci k nowledge is ava ilab le for establ ishi ng e ffic ie nt a nd ada pted oral vacci nat ion pr ograms a imed at el im inati ng terrestria l rabies fr om th is area. Pr ogress has bee n made i n a pplying oral rab ies vacc inat ion t o c onta in a nd e limi nate s ome strai ns of terrestr ial rab ies i n N orth Amer ica.42 N otable exam ples i nc lude near elimi nati on of rab ies fr om red foxes in s outher n Ontar io. C ontai nme nt a nd elim inat ion of ca nine rabies c oyotes fr om s outh Texas, c onta inme nt a nd near el im inat ion of racc oon rab ies fr om Oh io, preve nt ion of racc oon rabies s pread thr ough the Lake Cham pla in Valle y i n New York a nd acr oss northe m Verm ont a nd New Ham psh ire, a nd red uced inc ide nce of rab ies where other ora l rab ies vacci nati on pr ojects targeti ng racc oons have occ urred. As of 2005, b oth Ontar io a nd New Br unsw ick were free of racc oon rabies for greater tha n 10 m onths a nd 2 year s, res pectivel y, a fter im pleme ntat ion of'point infect ion c ontr ol 'strateg ies 29 b ut c onti nued s urve illa nce is crit ical t o m onit or e ffective ness. Rab ora IV -RG is the onl y rabies vacci ne lice nsed for use in the United States. It has not pr od uced s uffic ie nt levels of populat ion imm unit y i n sk unks i n the w ild at the c urre nt d ose a nd V-RG ma y be less e ffect ive in sk unks tha n other s pecies. Sk unks are a maj or c ontr ib ut or t or abie s in N orth fuller ica with 38% of cases ass ociate d w ith the racc oon varia nt of rabies virus inv olved sk unks i n 2001Y This has ra ised c onc er ns ab out a n inde pe nde nt ma inte na nce c yc le for racc oon rab ies i n sk unks. The nat ional rabies ma nageme nt g oals of v ir us c ontai nme nt a nd e limi nat ion of w li ll ki el y rema in e lus ive unt il a n oral vacc ine is l ice nsed that is imm unoge nic i n all terrestr ial rab ies reserv oir s pec ies. Sk unk rabies v ir us, wh ich has the br oadest ge og ra ph iC d istr ib ut ion of all terrestr ial rab ies va ria nts in the USA ca n c urre ntl y be addressed onl y thr ough l ocal tra pnate- release or po pulatio n su ppressio n programs.4 2 A satis factor y vacci ne for oral mass vaccinatio n o f sku nks has not yet bee n develo ped. Ma ny ex perime ntal a nd commercia l- produced live-modi fied or recombi na nt-based oral rabies virus vacc ines have bee n tested in sku nks with co ntradicto ry results. An oral mod ified live rabies virus Vacci ne SAD B19, used i n stri ped sku nks was i nnocuous a nd ma y be sa fer a nd more effective i ns ku nks a fter oral vaccinatio n th an previousl y co nsidered.46 An atte nuated SAG- 2 vacc ine was efficacious i n challe nge st ud ies i n sku nks a nd raccoo ns and ma y satis fy both s afet y and e fficac y co nce rns for or al rabies vaccinatio n o fm ajor North American rabies rese rvo ris.4 7 Duri ng the 1990s i n the United States, oral vacci natio n programs co nce ntrated u po n raccoo ns, g ra y foxes, a nd co yote, with similar success. As a result, raccoo n r abies has not s pread west o f its i nitial co nce ntratio n i n the easter n states, a nd gre y fox rabies i n co ntai ned i n the west ce ntral Texas, a nd no rece nt cases o fr abies have bee n re ported i n co yotes awa y from the Mexica n border for several years. However, vacci natio n is not a pa nacea a nd should be co nsidered as a ni m por ta nt adju nct to traditio nal preve ntio n a nd co ntrol tech niques i nh uma n a nd veteri na ry medici ne. It is notable that no practical vacc inatio n methods have bee n develo ped for bats.36 Phyloge netic a nal yses o f viruses from bats a nd car nivores suggest a historical basis for still existi ng vira l orig ins due to i nteractio ns betwee n these taxa. Thus the possibilit y for pathoge n emerge nce re su tli ng from tra nsmissio n b yr abid bats with subseque nt per petuatio n amo ng other a nimals ca nnot be discou nted easil y o n a ny co nti ne nt. Vam pire bats have bee n vacci nated 1M, scari ficat io n, ora l, or aerosol routes usi ng a vacci na-rabi es g lyco protei n recombi na nt vacci ne 48 The highest a ntibod y titers occu rred i na mmals vacc inated b y the 1M a nd scari ficatio n routes. All a nimals va cci nated b y the 1M, scari ficatio n, a nd oral routes su rvived ex perime ntal challe nge, exce pt 1 o f 8 receivi ng the aeosol vacci natio n died. Most co nsiste nt prog ress was achieved a nd mai ntai ned where : , Large cohere nt territor ies coveri ng certai n sized areas were treated simulta neousl y •. All areas o f fox habitat were included b yu si ng both ma nual a nd aerial distr ibutio n • Vacci natio n zo nes were progre SSivel y ex pa nded towards the i nfected area • At least t wo vacci natio ns were do ne • The bait de nsit y was a certai n mi nimum. The vacci natio n will succeed i n reduci ng or eradicati ng rabies o nl y i f a su fficie nt pro portio n o f the target po pu- 1atio n ca n be immu nized. Mathematical modeli ng tech niques are now bei ng tested to exami ne the po pulatio n biolog y o f rabies i n wildli fe s pecies such as raccoo ns a nd sk mlli:s 49 Mass immu nizatio n o f foxes b y aerial distributio n o f vacci nebaits co ntai ni ng liquid rabies vacci ne was highl y success ful i n co ntrolli ng rabies i n both mba na nd rural areas o fO ntari 036,42 I n 1989, the Ontario bega n a 5- year ex perime nt to elimi nate terrestrial rabies from a stud y area i n the easter n e nd o f souther n Ontario.50 Baits co ntai ni ng oral rabies vacci ne were dro pped a nnuall y i n the area at a de nsit y o f 20 baits/km 2 from 1989 to 1995. The ex perime nt was successful i n elimi nati ng the arctic fox varia nt o f rabies from the e ntire area. I n the 1980s, a n average o f 235 rabid foxes per year were re ported i nt he stud y area. Betwee n 1993 a nd 2001, no cases were re ported. Cases o f fox rabies i n other s pecies also disa ppeared. I n1 995, the last bovi ne a nd com pa nio n a nimal cases were re por ted a nd i n1 996 the last rabid sku nk occurred. Onl yb at varia nts o fr abies were prese nt u ntil 1999, whe n the raccoo n varia nt e ntered from New York. Quarantine and biosecu rity The most e ffective method o f preve nti ng the e ntry o f rabies i nto a cou ntry free o f the disease is the im positio n o f a quara nti ne period o f 4-6 mo nths o n all im ported dogs. This s ystem has successfull y preve nted the e ntr y o f the disease i nto isla nd cou ntries, but has obvious limitatio n i n cou ntries that have la nd borders. The occurre nce o ft he disease i n two dogs i n the United Ki ngdom i n 1969-1970 i nw hich the i ncubatio n period a ppeared to last 7-9 mo nths suggests that the more usual period o f 6 mo nths ma y give i ncom plete protectio n. There fore, vacci natio n o n two occasio ns with a n i nactivated vacci ne while the a nimal is still i n quara nti ne for 6 mo nths is the curre nt recomme ndatio n. To require a lo nger period o f quara nti ne would e ncourage evasio n o f the law b y smuggli ng. The situatio n i n the United Ki ngdom, a nd i n a ny cou ntr y where the d isease does not occur, is a vexed o ne. It is possible to rel y chie fl yo nq uara nti ne a nd act swi ftl y to stam p the disease out i f it occurs. The shoc k e radicatio n program would i nclude quara nti ne o f, a nd vaccinatio n i n, a risk area, ri ng vacci natio n arou nd it, a nd destructio n o f a ll wildli fe. This procedure is likel y to be ado pted i n cou ntries where the risk is small, such as Australia. Where the risk is great, co nsideratio n must be give n to mass vaccinatio n o f wildli fe b y baits, because wildli fe are the cracks i n the de fe nse armor. The use o f combi ned vacci r'les co ntai nirlg rabies vacci ne i no ther vacci nes used i nd ogs wou ld be a n e ffective a nd pa nic-f ree wa y o fi ncreasi ng the immu ne status o ft he pet po pulatio n. REV I EW LITE RATURE Frost AK, Hamir AN. The North American Raccoon Rabies. Epizootic Vet l3uIl 1998; 68:1343-1349. Krebs JW, Rupprecht CE, Childs JE. Rabies surveillance in the United States during 1999. J Am Vet Med Assoc 2000; 217:1799-1811. Krebs JW et al. Rabies surveillance in the United States during 2000. J Am Vet Med Assoc 2001; 219:1687-1699. Krebs JW et al. Rabies surveillance in the United States during 2001. J Am Vet Med Assoc 2002; 221:1690-1701. Rupprecht CE, Hanlon CA, Hemachudka T Rabies reexamined. Lancet Infect Dis 2002; 2: 327-343. Woldehiwet Z. Rabies: recent developments. Res Vet Sci 2002; 73:17-25. Krebs JW, Wheeling IT, Childs JE. Rabies surveillance in the United States during 2002. J Am Vet Med Assoc 2003; 223:1736-1748. Krebs JW et al. Rabies surveillance in the United States during 2003. J Am Vet Med Assoc 2004; 225:1837-1849. Warrell MJ, Warrell DA. Rabies and other lyssavirus diseases. Lancet 2004; 363:959-969. l3ellotto A et al. Overview of rabies in the Americas Virus Res 2005; 111:5-12. Slate D et al. Status of oral rabies vaccination in wild carnivores in the United States. Virus Res 2005; 111:68-76. REFERENCES 1. Rupprecht CE, Hanlon CA, Hemachudka T Lancet Infect Dis 2002; 2:327. 2. Frost AK, Hamir AN. Vet l3uIl 1998; 68:1343. 3. Woldehiwet Z. Res Vet Sci 2002; 73:17. 4. Warrell NlJ, Warrell DA. Lancet 2004; 363:959. 5. Zienius D et al. Vet Microbiol 2003; 93:91. 6. AliYH. Vet Rec 2002; 130:610. 7. Chaparro F, Esterhuysen JJ. Onderst J Vet Res 1993; 60:373. 8. Casey G A et al. Can Vet J 1996; 37:347. 9. Tinline RR, MacInnes CD. J Wildlife Dis 2004; 40:212. 10. Krebs JW et al. J Am Vet Med Assoc 2000; 217:1799. 11. Krebs JW et al. J Am Vet Med Assoc 2001; 219:1687. 12. Krebs JW et al. J Am Vet Med Assoc 2002; 221:1690. 13. Krebs JW et al. J Am Vet Med Assoc 2003; 223:1736. 14. Krebs JW et al. J Am Vet Med Assoc 2004; 225:1837. 15. Krebs JW et al. J Wildlife Dis 2003; 39:253. 16. Childs JE et al. Proc Natl Acad Sci US 2000; 97:13666. 17. Mondul AM et al. J Am Vet Med Assoc 2003; 222:633. 18. l3adrane H, Tordo N. JVirol 2001; 75:8096. 19. Picard-Meyer E et al.Vet Rec 2004; 134:589. 20. l3rookes SM et al. Emerg Infect Dis 2005; 11:572. 21. Guerra MA et al. Emerg Infect Dis 2003; 9:1143. 22. de Mattos CA et al. J Wildlife Dis 2000; 36:231. 23. Wright A et al. Vet Microbiol 2002; 87:95. 24. Totton SC et al. J Wildlife Dis 2002; 38:313. 25. Jenkins S et al. J Am Vet Med Assoc 2005; 226:1304. 26. Kresta AE, Henka SE. J Anim Vet Advan 2002; 1:63. 27. Willoughby RE et al. New Eng J Med 2005; 352:2508 PART 2 SPECIAL M EDICINE • Chapte' 22, 28. Bellotto A et al.Virus Res 2005; 111:5. 29. Rosatte R et al. J Wildlife Dis 2001; 37:265. 30. Hudson LC et al. J Vet Med B 1996; 43:277. 31. Green SL et al. J Am Vet Med Assoc 1992; 200:1133. 32. Bingham J, van der Merwe M. J Virol Methods ' . - " 2002; 101:85. 33. Jayakumar R et al. Comp Immunol Microbiol Infect Dis 1995; 18:269. 34. David D et al. Vet Microbiol 2002; 87:111. 35. Asian A et a\. Vet Rec 2004; 155:550. 36. Rupprecht CE et al. Dev Bioi (Basel) 2004; 119:173. 37. Trevejo RT. J Am Vet Med Assoc 2000; 217:1647. 38. Murray KG, Arguin PM. J Am Vet Med Assoc 2000; 216:188. 39. Madhusudana SN et al. Int J Infect Dis 2004; 8:339. 40. Wilson PJ, Clark KA. J Am Vet Med Assoc 2001; 218:522. 41. Larghi OP Dev Bioi (Basel) 2004; 119:205. 42. Slate D et al. Virus Res 2005; 111:68. 43. Cliquet F, Aubert M. Dev Bioi (Basel) 2004; 1 19:185. 44. Rosatte RC, Lawson KF. J Wildlife Dis 2001; 37:730. 45. Vos A. JVet Med B 2003; 50:477. 46. Vos A et al. J Wildlife Dis 2002; 38:428. 47. Hanlon CA et a\. J Wildlife Dis 2002; 38:420. 48. Aguilar-Setien A et a\. J Wildlife Dis 2002; 38:539. 49. Broadfoot JD et al. Ecol Appl 2001; 11:295. 50. Maclnnes CD et al. J Wildlife Dis 2001; 37:119.