Rabies surveillance in the United States during 1999

Zoonotic Viral Diseases of Equines and Their Impact on Human and Animal Health

INTRODUCTION

Zoonotic diseases are the infectious diseases that can be transmitted to human beings and vice versa from animals either directly or indirectly. These diseases can be caused by a range of organisms including bacteria, parasites, viruses and fungi. Viral diseases are highly infectious and capable of causing pandemics as evidenced by outbreaks of diseases like Ebola, Middle East Respiratory Syndrome, West Nile, SARS-Corona, Nipah, Hendra, Avian influenza and Swine influenza.

EXPALANTION

Many viruses affecting equines are also important human pathogens. Diseases like Eastern equine encephalitis (EEE), Western equine encephalitis (WEE), and Venezuelan-equine encephalitis (VEE) are highly infectious and can be disseminated as aerosols. A large number of horses and human cases of VEE with fatal encephalitis have continuously occurred in Venezuela and Colombia. Vesicular stomatitis (VS) is prevalent in horses in North America and has zoonotic potential causing encephalitis in children. Hendra virus (HeV) causes respiratory and neurological disease and death in man and horses. Since its first outbreak in 1994, 53 disease incidents have been reported in Australia. West Nile fever has spread to many newer territories across continents during recent years.It has been described in Africa, Europe, South Asia, Oceania and North America. Japanese encephalitis has expanded horizons from Asia to western Pacific region including the eastern Indonesian archipelago, Papua New Guinea and Australia. Rabies is rare in horses but still a public health concern being a fatal disease. Equine influenza is historically not known to affect humans but many scientists have mixed opinions. Equine viral diseases of zoonotic importance and their impact on animal and human health have been elaborated in this article.

CONCLUSION

Equine viral diseases though restricted to certain geographical areas have huge impact on equine and human health. Diseases like West Nile fever, Hendra, VS, VEE, EEE, JE, Rabies have the potential for spread and ability to cause disease in human. Equine influenza is historically not known to affect humans but some experimental and observational evidence show that H3N8 influenza virus has infected man. Despite our pursuit of understanding the complexity of the vector-host-pathogen mediating disease transmission, it is not possible to make generalized predictions concerning the degree of impact of disease emergence. A targeted, multidisciplinary effort is required to understand the risk factors for zoonosis and apply the interventions necessary to control it.

Novel Approaches to the Prevention and Treatment of Rabies

Rabies is a highly lethal disease caused by the neurotropic rabies virus (RABV), and it remains an important public health problem globally. Effective vaccines have been developed for pre- and post-exposure prophylaxis (PEP). PEP is only effective if it is initiated promptly after recognizing exposure. Once neurological symptoms develop, however, it is widely accepted that there is no effective treatment available. Recent studies indicate that the presence of RABV-specific immunity (i.e. Virus neutralizing antibodies, VNA) and the transient enhancement of the BBB permeability are absolutely required for effective virus clearance from the CNS. In principle, it has been shown in mice using various live-attenuated RABVs or recombinant RABVs expressing three copies of the G or expressing chemokine/cytokines, which can induce high levels of VNA in the serum and also capable of transiently enhancing the BBB permeability that it is possible to clear the virus from CNS. Also, it has been demonstrated that, intravenous administration of VNA together with MCP-1 (shown to transiently open up BBB) can clear RABV from the CNS in both immunocompetent and immunocompromised mice, as late as 5 days after lethal challenge. Novel therapeutic approaches aimed at allowing the peripheral VNA to cross the BBB by administration of the VNA in combination with biological or chemical agents that can transiently open up the BBB would be useful to establish an effective therapy for rabies in humans. In this review, we focus on the some of the approaches that can be used to meet the challenges in the field of rabies treatment.

Australian bat lyssavirus infection in two horses

In May 2013, the first cases of Australian bat lyssavirus infections in domestic animals were identified in Australia. Two horses (filly-H1 and gelding-H2) were infected with the Yellow-bellied sheathtail bat (YBST) variant of Australian bat lyssavirus (ABLV). The horses presented with neurological signs, pyrexia and progressing ataxia. Intra-cytoplasmic inclusion bodies (Negri bodies) were detected in some Purkinje neurons in haematoxylin and eosin (H&E) stained sections from the brain of one of the two infected horses (H2) by histological examination. A morphological diagnosis of sub-acute moderate non-suppurative, predominantly angiocentric, meningo-encephalomyelitis of viral aetiology was made. The presumptive diagnosis of ABLV infection was confirmed by the positive testing of the affected brain tissue from (H2) in a range of laboratory tests including fluorescent antibody test (FAT) and real-time PCR targeting the nucleocapsid (N) gene. Retrospective testing of the oral swab from (H1) in the real-time PCR also returned a positive result. The FAT and immunohistochemistry (IHC) revealed an abundance of ABLV antigen throughout the examined brain sections. ABLV was isolated from the brain (H2) and oral swab/saliva (H1) in the neuroblastoma cell line (MNA). Alignment of the genome sequence revealed a 97.7% identity with the YBST ABLV strain.

Humoral immune response to oral rabies vaccination in raccoon kits: problems and implications

Little is known about the immunogenicity of RABORAL V-RG(®) (V-RG), an oral rabies vaccine, in raccoon kits (Procyon lotor). The objectives of this study were to characterize the immunogenicity of V-RG in young kits and investigate the potential impact of maternal antibodies on response to vaccination of nursing raccoon kits. Raccoon kits (n=30) were vaccinated at either 3 weeks of age, 7 weeks of age, or assigned as contact controls. Nineteen kits (73%) that were whelped by unvaccinated mothers responded to V-RG exposure (orally or indirect contact) by production of detectable rabies virus neutralizing antibodies (RVNA) while 7 (27%) kits did not respond to V-RG exposure. Four kits were whelped by a mother with high levels of RVNA and all four kits acquired maternal rabies antibodies. At approximately 9 months of age, all kits were inoculated with a killed rabies vaccine, IMRAB3(®). The kits which initially responded to V-RG oral vaccination or contact with vaccinated littermates demonstrated a rapid anamnestic response. In contrast, the V-RG non-responders and those with acquired maternal antibodies exhibited a primary immune response to IMRAB3(®), where RVNA levels were substantially lower on days 5 and 7 than the levels in the animals with an anamnestic response. These findings suggest that the naïve contact kits and the nonresponsive kits most likely remained susceptible to rabies virus infection whereas the ones demonstrating response to V-RG would not have been susceptible to a rabies virus infection.

Ecology of zoonotic infectious diseases in bats: current knowledge and future directions

Bats are hosts to a range of zoonotic and potentially zoonotic pathogens. Human activities that increase exposure to bats will likely increase the opportunity for infections to spill over in the future. Ecological drivers of pathogen spillover and emergence in novel hosts, including humans, involve a complex mixture of processes, and understanding these complexities may aid in predicting spillover. In particular, only once the pathogen and host ecologies are known can the impacts of anthropogenic changes be fully appreciated. Cross-disciplinary approaches are required to understand how host and pathogen ecology interact. Bats differ from other sylvatic disease reservoirs because of their unique and diverse lifestyles, including their ability to fly, often highly gregarious social structures, long lifespans and low fecundity rates. We highlight how these traits may affect infection dynamics and how both host and pathogen traits may interact to affect infection dynamics. We identify key questions relating to the ecology of infectious diseases in bats and propose that a combination of field and laboratory studies are needed to create data-driven mechanistic models to elucidate those aspects of bat ecology that are most critical to the dynamics of emerging bat viruses. If commonalities can be found, then predicting the dynamics of newly emerging diseases may be possible. This modelling approach will be particularly important in scenarios when population surveillance data are unavailable and when it is unclear which aspects of host ecology are driving infection dynamics.

Seroprevalence of rabies virus antibodies in bats from southern China

Members of the Order Chiroptera are the natural reservoirs of lyssaviruses and play an important role in the transmission of rabies to animals and humans. In this present study, the seroprevalence for rabies virus was determined for bats sampled from four southern provinces on the Chinese mainland. A total of 685 bats of 8 species representing 4 families were collected from 10 sites, and were tested by the indirect fluorescent antibody test using fluorescein isothiocyanate (FITC)-conjugated protein A/G mixture and viral neutralization test. Rabies antibody response was only detected from three bat species (Rousettus leschenaulti, Rhinolophus blythi, and Rhinolophus ferrumequinum). The overall rabies seroconversion rate was only 2.2% (15/685). Of the 15 positive sera, 13 (12 fruit bats and 1 insectivorous bat) were indirect fluorescent antibody test positive, and two insectivorous bats were virus neutralization positive when tested by the modified fluorescent antibody viral neutralization test, albeit extremely low. To our knowledge, this is the first published report describing rabies seroprevalences from Chinese bats. These results suggest that bats may play a role in the ecology of lyssaviruses in China, and further surveillance for the presence of lyssaviruses in bats should be undertaken throughout the country and extended to other species.

Nutrition and behavior of striped skunks

Skunks are an integral part of the environment and a fascinating component of the earth's biodiversity. Their behavioral idiosyncrasies, made possible by their unique method of defense, make them entertaining to watch in the wild, and their beneficial habits far outweigh any potential negative attributes. Striped skunks can be a benefit in urban and agricultural areas because they prey on harmful and damaging insects and rodents that plague gardens and crops. The general public should be encouraged to live in harmony with skunks, as opposed to viewing them as nuisances. Keeping captive or pet skunks should be considered only after feeding, care, disease, and legal information has been investigated.

Quantitative assessment of the risk of rabies entering Japan through the importation of dogs and cats from the USA

Up to October 2004, dogs and cats imported into Japan were subjected to a quarantine regimen which consisted of vaccination and a 30- to 365-day waiting period in the country of origin and a 14-day quarantine period upon arrival in Japan. This regimen was replaced by a new one, consisting of vaccination, antibody level titration and a 180-day waiting period in the country of origin, in November 2004. To evaluate the effect of this policy change, a quantitative risk assessment was undertaken. The risk of rabies entering Japan through the importation of dogs and cats from the USA under the old – and new – regimens was quantitatively assessed and compared. Under the new regimen, rabies will enter Japan once every 4932 years (90% confidence interval 1812–13 412 years) through the importation of dogs and cats from the USA. Under the old regimen, rabies would enter Japan once every 70 years (39–205 years), 83 years (45–267 years) or 190 years (104–609 years) assuming that the animal departs the country of origin 30 days, 180 days or 365 days after vaccination, respectively. This indicates the policy change would reduce the risk by a factor of 1/25–1/70.

Rabies in small animals

Rabies in small animals has been dramatically reduced in the United States since the introduction of rabies vaccination of domestic animals in the 1940s. As a consequence, the number of human rabies cases has declined to only a couple per year. During the past several years, the dog rabies variant has almost disappeared completely. Rabies in wildlife has skyrocketed, however. Each wildlife species carries its own rabies variant(s). These wildlife epizootics present a constant public health threat in addition to the danger of reintroducing rabies to domestic animals. Vaccination is the key to prevent rabies in small animals and rabies transmission to human beings.

Rabies virus infection in a pet guinea pig and seven pet rabbits

Raccoon-variant rabies was confirmed in 7 pet rabbits and 1 pet guinea pig in New York State, and postexposure treatment was required in several adults and children. To prevent rabies virus infection, domestic rabbits and pet rodents should be protected from contact with wild animals, including double-cage housing when housed outside. Pet rabbits or rodents with any possible contact with a wild animal, particularly if the rabbit or rodent had wounds of unknown origin, should be quarantined for 6 months for observation, to prevent escape, and to avoid contact with humans, who will require treatment if the rabbit or rodent develops rabies. Bites and scratches to humans from rodents and lagomorphs should be evaluated for potential rabies exposure on an individual basis, with consideration of whether the animal was caged outside or permitted outdoors unsupervised.

Quantitative risk assessment of rabies entering Great Britain from North America via cats and dogs

Great Britain has been rabies-free since 1922, which is often considered to be in part due to the strict laws requiring that imported cats and dogs be vaccinated and quarantined for 6 months immediately on entry into the country. Except for two isolated incidents, this quarantine policy has contributed to ensuring that Great Britain has remained free of rabies. In 2000, amendments to the UK quarantine laws were made and the Pet Travel Scheme (PETS) was launched for companion animals traveling from European Union countries and rabies-free islands. Since its introduction, it has been proposed that other countries including North America should be included within the UK scheme. A quantitative risk assessment was developed to assist in the policy decision to amend the long-standing quarantine laws for dogs and cats from North America. It was determined that the risk of rabies entry is very low and is dependent on the level of compliance (i.e., legally conforming to all of the required regulations) with PETS and the number of pets imported. Assuming 100% compliance with PETS and the current level of importation of cats and dogs from North America, the annual probability of importing rabies is lower for animals traveling via PETS (7.22 x 10(-6), 95th percentile) than quarantine (1.01 x 10(-5), 95th percentile). These results, and other scientific evidence, directly informed the decision to expand the PETS scheme to North America as of December 2002.

Herbarium studies on the distribution of anther-smut fungus (Microbotryum violaceum) and Silene species (Caryophyllaceae) in the eastern United States

We used herbarium specimens of Silene virginica, S. caroliniana, S. rotundifolia, and S. latifolia to survey the incidence of anther-smut disease (caused by Microbotryum violaceum sensu lato) in the eastern USA. We found no evidence of a collector bias against diseased specimens. Diseased specimens were frequently found in collections of S. virginica and S. caroliniana, but not in those of S. rotundifolia or S. latifolia. Disease incidence in S. virginica and S. caroliniana increased significantly over the past century and was higher in marginal populations. The absence of disease in specimens of S. rotundifolia is consistent with field observations, but its presence in natural populations of S. latifolia (especially in Virginia) suggests that the disease is recently introduced. Changes in the host distributions were also evident. The relative abundance of S. caroliniana declined over time (especially further north), while the relative abundance of S. virginica increased. Silene latifolia was absent or rare south of Pennsylvania before ca. 1920, indicating that S. latifolia and its anther smut are likely to be recent introductions in Virginia. Methods are also presented that quantify the completeness of coverage provided by herbarium specimens.

Feline injection site sarcomas

Injection site sarcomas in cats have been the topic of more than 40 articles and over 20 scientific abstracts as well as multiple letters to veterinary journals, articles in the popular press, and Internet-based web sites. With the level of discussion that has surrounded this tumor entity, one might expect that great strides have been made in determining the etiology, epidemiology, and preferred treatment options for this disease. Nearly half of the publications on this subject are review articles, however, and that alone indicates both the high level of interest and the lack of information in this situation. This article summarizes the development of our current understanding of this tumor with regard to areas of research into the cause of injection site sarcomas, epidemiology, and the current standard of care for treatment of this iatrogenic disease.

Rabies epizootics among raccoons vary along a North-South gradient in the Eastern United States

The characteristics of rabies epizootics among raccoons were investigated in 11 eastern states along a North-South gradient from New York to North Carolina. Epizootics were defined as discrete intervals of time of at least 5 months in duration, when reported cases of raccoon rabies from an individual county exceeded the median value of raccoon rabies cases reported by that county over the entire period rabies was present among raccoons in the county. Over the approximately 20-year study period, 35,000 cases of raccoon rabies were reported, and epizootics were detected from 251 (64.4%) of 390 counties. The median annual incidence was 0.14 epizootics per year. During the first defined epizootic in a county, the median total number of raccoons reported rabid was 47, with a median monthly incidence of rabies in raccoons of 3.1. The median lag time from the first report of a rabid raccoon in a county to the beginning of the first epizootic was 4 months. Significant differences in the annual incidence of epizootics and monthly incidence of rabid raccoons during epizootics were observed among different states. Although human population density and per capita health spending within counties were positively associated with increasing magnitude of epizootics, a significant difference in the characteristics of rabies epizootics in northern and southern states was apparent. We hypothesize that environmental conditions and perhaps human influence resulted in rabies epizootics in southern states that were smaller, less-frequent, and lacking in well-defined temporal structure compared with those in northern states.

Cryptogenic rabies, bats, and the question of aerosol transmission

Human rabies is rare in the United States; however, an estimated 40,000 patients receive rabies postexposure prophylaxis each year. Misconceptions about the transmission of rabies are plentiful, particularly regarding bats. Most cases of human rabies caused by bat variants have no definitive history of animal bite. Three hypotheses are proposed and reviewed for the transmission of rabies from bats to human beings. They include nonbite transmission (including aerosol transmission), the alternate host hypothesis (an intermediate animal host that acquires rabies from a bat and then transmits rabies to human beings), and minimized or unrecognized bat bites. Nonbite transmission of rabies is very rare, and aerosol transmission has never been well documented in the natural environment. The known pathogenesis of rabies and available data suggest that all or nearly all cases of human rabies attributable to bats were transmitted by bat bites that were minimized or unrecognized by the patients.

Serologic evidence of Lyssavirus infections among bats, the Philippines

Active surveillance for lyssaviruses was conducted among populations of bats in the Philippines. The presence of past or current Lyssavirus infection was determined by use of direct fluorescent antibody assays on bat brains and virus neutralization assays on bat sera. Although no bats were found to have active infection with a Lyssavirus, 22 had evidence of neutralizing antibody against the Australian bat lyssavirus (ABLV). Seropositivity was statistically associated with one species of bat, Miniopterus schreibersi. Results from the virus neutralization assays are consistent with the presence in the Philippines of a naturally occurring Lyssavirus related to ABLV.

Cost of distributing oral raccoon-variant rabies vaccine in Ohio: 1997-2000

OBJECTIVE

Analysis of the cost of 8 distributions of oral rabies vaccine (ORV) with strains known to infect raccoons in Ohio between 1997 and 2000.

DESIGN

Original study.

PROCEDURE

Fishmeal bait containing ORV was distributed on foot, by vehicle, and by helicopter and fixed-wing aircraft. The cost of personnel, vehicles, and helicopter and aircraft use and other associated expenses were obtained from field records and interviews with personnel and agencies involved in the ORV program.

RESULTS

Each bait distribution lasted approximately 1 week. Areas baited ranged from 1,701 km2 to 6,497 km2. Density varied for each distribution, with means of 79 baits/km2 for ground baiting and 93 baits/km2 for aerial baiting. Typically, 72 people participated in the ground portion of each distribution and 32 in the aerial portion. The cost of ground baiting (mean +/- SD, 19.24 dollars/km2 +/- 6.35 dollars/km2) was consistently less than that for air baiting (mean +/- SD, 24.71 dollars/km2 +/- 4.65 dollars/kml) for each distribution. The total cost of distribution varied from 30,568 dollars to 145,842 dollars (mean, 96,791 dollars), and bait cost varied from 150,714 dollars to 1,029,423 dollars (mean, 543,839 dollars). The total cost of ORV distributions ranged from 102 dollars/km2 to 261 dollars/km2 (mean, 153 dollars/km2).

CONCLUSIONS

In the United States, rabies strains that infect raccoons have been responsible for the largest increase in rabies in animals in the past 3 decades. Use of ORV is a promising new tool that can be used to control rabies in raccoons. Documenting the estimated cost of implementing an ORV program may lead to more efficient use of resources to control and limit the spread of rabies. In addition, accurately measured distribution costs can be used to perform an economic cost-benefit analysis for an ORV program.

Rabies surveillance in the United States during 2000

During 2000, 49 states, the District of Columbia, and Puerto Rico reported 7,364 cases of rabies in nonhuman animals and 5 cases in human beings to the Centers for Disease Control and Prevention, an increase of 4.3% from 7,067 cases in nonhuman animals reported in 1999. Ninety-three percent (6,855 cases) were in wild animals, whereas 6.9% (509 cases) were in domestic species (compared wth 91.5% in wild animals and 8.5% in domestic species in 1999). Compared with cases reported in 1999, the number of cases reported in 2000 increased among bats, dogs, foxes, skunks, and sheep/goats and decreased among cats, cattle, horses/mules, raccoons, and swine. The relative contributions of the major groups of animals were as follows: raccoons (37.7%; 2,778 cases), skunks (30.2%; 2,223), bats (16.8%; 1,240), foxes (6.2%; 453), cats (3.4%; 249), dogs (1.6%; 114), and cattle (1.1%; 83). Ten of the 19 states where the raccoon-associated variant of the rabies virus has been enzootic reported increases in the numbers of cases of rabies during 2000. Among those states that have engaged in extensive wildlife rabies control programs, no cases of rabies associated with the epizootic of rabies in raccoons (or in any other terrestrial species) were reported in Ohio, compared with 6 cases reported in 1999. No rabies cases associated with the dog/coyote variant (compared with 10 cases in 1999, including 5 in dogs) were reported in Texas, and cases associated with the gray fox variant of the virus decreased (58 cases in 2000, including 38 among foxes). Reports of rabid skunks exceeded those of rabid raccoons in Massachusetts and Rhode Island, states with enzootic raccoon rabies, for the fourth consecutive year. Nationally, the number of rabies cases in skunks increased by 7.1% from that reported in 1999. The greatest numerical increase in rabid skunks (550 cases in 2000, compared with 192 in 1999) was reported in Texas. The number of cases of rabies reported in bats (1,240) during 2000 increased 25.4% over the number reported during 1999 (989) and represented the greatest contribution (16.8% of the total number of rabid animals) ever recorded for this group of mammals. Cases of rabies reported in cattle (83) and cats (249) decreased by 38.5% and 10.4%, respectively, whereas cases in dogs (114) increased by 2.7% over those reported in 1999. Reported cases of rabies among horses and mules declined 20% from 65 cases in 1999 to 52 cases in 2000. Four indigenously acquired cases of rabies reported in human beings were caused by variants of the rabies virus associated with bats. One case of human rabies acquired outside the United States that resulted from a dog bite was caused by the canine variant of the rabies virus.

Epidemiologic characteristics of rabies virus variants in dogs and cats in the United States, 1999

OBJECTIVE

To evaluate epidemiologic features of rabies virus variants in dogs and cats in the United States during 1999 and assess the role of bat-associated variants.

DESIGN

Epidemiologic survey.

SAMPLE POPULATION

Rabies viruses from 78 dogs and 230 cats.

PROCEDURE

Brain specimens from rabid dogs and cats were submitted for typing of rabies virus. Historical information, including ownership and vaccination status, was obtained for each animal. Specimens were typed by use of indirect fluorescent antibody assay or reverse transcriptase polymerase chain reaction assay and nucleotide sequence analysis.

RESULTS

Nearly all animals were infected with the predicted terrestrial rabies virus variant associated with the geographic location of the submission. A bat-associated variant of rabies virus was found in a single cat from Maryland. More than half (53%) of submitted animals were classified as owned animals, and most had no known history of vaccination. One vaccination failure was reported in a dog that did not receive a booster dose of rabies vaccine after exposure to a possibly rabid animal.

CONCLUSIONS AND CLINICAL RELEVANCE

Bat-associated rabies virus variants were not a common cause of rabies in dogs and cats during 1999. Vaccine failures were uncommon during the study period. Because most rabid dogs and cats were unvaccinated and were owned animals rather than strays, educational campaigns targeting owners may be useful.