Genetic divergence of rabies viruses from bat species of Colorado, USA

Molecular epidemiological studies have linked many cryptic human rabies cases in the United States with exposure to rabies virus (RV) variants associated with insectivorous bats. In Colorado, bats accounted for 98% of all reported animal rabies cases between 1977 and 1996. The genetic divergence of RV was investigated in bat and terrestrial animal specimens that were submitted for rabies diagnosis to the Colorado Department of Public Health and Environment (CDPHE), Colorado, USA. RV isolates from animal specimens across the United States were also included in the analysis. Phylogenetic analyses were performed on partial nucleoprotein (N) gene sequences, which revealed seven principal clades. RV associated with the colonial big brown bat, Eptesicus fuscus, an bats of the genus Myotis were found to segregate into two distinct clades (I and IV). Clade I was harbored by E. fuscus and Myotis species, but was also identified in terrestrial animals such as domestic cats and striped skunks (Mephitis mephitis). Clade IV was divided into subclades IVA, IVB, and IVC; IVA was identified in E. fuscus, and Myotis species bats, and also in a fox; subclades IVB and IVC circulated predominantly in E. fuscus. Clade II was formed by big free-tailed bat (Nyctinomops macrotis) and striped skunk (Mephitis mephitis) samples. Clade III included RVs that are maintained by generally solitary, migratory bats such as the silver-haired bat (Lasionycteris noctivagans) and bats of the genus Lasiurus. Big brown bats were found to harbor this RV variant. None of the Colorado specimens segregated with clades V and VII that harbor RVs associated with terrestrial animals. Different species of bats had the same RV variant, indicating active inter-species rabies transmission. In Colorado, animal rabies occurs principally in bats, and the identification of bat RVs in cat, gray fox Urocyon cinereoargenteus), and striped skunks demonstrated the importance of rabies spillover from bats to domestic and terrestrial wildlife species.     

Emerging aspects of rabies infection: with a special emphasis on children

PURPOSE OF REVIEW: Increased awareness of the long-neglected rabies virus could promote the highly effective methods of preventing human deaths. Rabies and rabies-related lyssaviruses have recently been appearing in unexpected places, sometimes with dire consequences. Although rabies of canine origin remains 100% fatal in human beings, should the surprising recovery of a single unvaccinated child influence treatment now? RECENT FINDINGS: Evidence of rabies-related lyssavirus infection of bats is increasing across continents and with new virus types. Human rabies has been misdiagnosed as cerebral malaria, or even drug abuse. Organ transplant recipients have been infected. The first unvaccinated patient, a teenager, bitten by a bat, recovered from rabies encephalitis, but why might this be? Highly effective control and prevention of infection is possible. Preexposure prophylaxis for schoolchildren could now become routine. Improved economical intradermal postexposure vaccine regimens could increase the availability of affordable treatment in developing countries. Controlling dog rabies could prevent 95% of human deaths, but education and resources are lacking. SUMMARY: The risks and problems of rabies and other lyssaviruses vary greatly across the world. Knowledge of epidemiology and prevention could save the lives of victims of animal bites and promote efforts to control and even eliminate dog rabies.     

Rabies in a nine-year-old child: The myth of the bite

A nine-year-old boy died from rabies encephalitis caused by a rabies virus variant associated with insectivorous bats. The patient was most likely infected in the Laurentian Mountains of western Quebec, but neither the patient nor his parents remembered any direct contact with an animal. The diagnosis was made seven days after the start of symptoms. After examining the most recent cases of rabies in North America, it is obvious that rabies following bat exposure can occur without history of a documented bite. The present case report emphasizes that the general public and medical care providers need better information about the risks associated with exposure to bats.Key Words: Bat, Children, Encephalitis, Prophylaxis, RabiesRabies is a zoonosis responsible for more than 50,000 human deaths every year worldwide, as reported by the World Health Organization. In North America and Europe, human rabies has become a very rare disease, because of the systematic vaccination of domestic animals, massive vaccination campaigns of wild animals, efficacy of rabies postexposure prophylaxis (RPEP) and education programs (1,2). While knowledge about the risk of rabies associated with a bite from a terrestrial animal seems relatively adequate among the general public and medical care providers, a lack of information may exist regarding the risk of human rabies following contact with a bat. Between 1980 and 1996, 32 cases of human rabies were diagnosed in the United States, 17 of which occurred after a contact with an indigenous bat (of which only two patients had a definite bite), 14 cases after a dog bite and one after a skunk bite (3). In Canada, three of the four cases of human rabies that have occurred since 1970 followed exposure to bats, the last case dating to 1985 (4). Since September 2000, five cases of human rabies have been reported in the United States (5). One was consecutive to a dog bite contracted in Africa and four have been attributed to bats; in the latter cases, a definite history of a bite was noted in only one case. In 1996, the National Association of State Public Health Veterinarians of the United States stated that "since rabies is endemic in bats, bats should be excluded from houses and surrounding structures to prevent direct association with humans" (6). Possible measures to reduce the bat population to a critical threshold below which the virus might be unable to propagate or to induce immunity in the vector via vaccination seem physically, economically and ecologically impractical (7). The case that we report emphasizes that the bite or the scratch of a rabid bat can go unnoticed and may lead to the development of human rabies.     

Towards Development of an Anti-Vampire Bat Vaccine for Rabies Management: Inoculation of Vampire Bat Saliva Induces Immune-Mediated Resistance

The common vampire bat (Desmodus rotundus) is a hematophagous species responsible for paralytic rabies and bite damage that affects livestock, humans and wildlife from Mexico to Argentina. Current measures to control vampires, based upon coumarin-derived poisons, are not used extensively due in part to the high cost of application, risks for bats that share roosts with vampires and residual environmental contamination. Observations that vampire bat bites may induce resistance in livestock against vampire bat salivary anticoagulants encourage research into novel vaccine-based alternatives particularly focused upon increasing livestock resistance to vampire salivary components. We evaluated the action of vampire bat saliva-Freund’s incomplete adjuvant administered to sheep with anticoagulant responses induced by repeated vampire bites in a control group and examined characteristics of vampire bat salivary secretion. We observed that injections induced a response against vampire bat salivary anticoagulants stronger than by repeated vampire bat bites. Based upon these preliminary findings, we hypothesize the utility of developing a control technique based on induction of an immunologically mediated resistance against vampire bat anticoagulants and rabies virus via dual delivery of appropriate host and pathogen antigens. Fundamental characteristics of host biology favor alternative strategies than simple culling by poisons for practical, economical, and ecologically relevant management of vampire populations within a One Health context.     

Circumstances of bat encounters and knowledge of rabies among Minnesota residents submitting bats for rabies testing

Minnesota residents who submitted a bat to the Minnesota Department of Health for rabies testing in 2003 were surveyed by telephone regarding the circumstances of the bat encounter and their knowledge of bats and rabies. Of 442 bats submitted for testing, 12 (3%) tested positive for rabies, and 410 (93%) tested negative; 17 (4%) bats were unsuitable for testing, and three (1%) had equivocal results. A case-control study found that rabid bats were more likely than non-rabid bats to be found in September, found outside, found in a wooded area, unable to fly, acting ill, or acting aggressively. Rabid bats were not more likely than non-rabid bats to be found during the day or to have bitten someone. While most persons submitting bats for rabies testing were aware that bats can carry rabies, few knew they should submit the bat for testing until they sought the advice of an animal control officer, veterinarian, or healthcare provider.     

Novel and Diverse Non-Rabies Rhabdoviruses Identified in Bats with Human Exposure,South Dakota,USA

Bats are a host and reservoir for a large number of viruses, many of which are zoonotic. In North America, the big brown bat (Eptesicus fuscus) is widely distributed and common. Big brown bats are a known reservoir for rabies virus, which, combined with their propensity to roost in human structures, necessitates testing for rabies virus following human exposure. The current pandemic caused by severe acute respiratory syndrome coronavirus 2, likely of bat origin, illustrates the need for continued surveillance of wildlife and bats for potentially emerging zoonotic viruses. Viral metagenomic sequencing was performed on 39 big brown bats and one hoary bat submitted for rabies testing due to human exposure in South Dakota. A new genotype of American bat vesiculovirus was identified in seven of 17 (41%) heart and lung homogenates at high levels in addition to two of 23 viscera pools. A second rhabdovirus, Sodak rhabdovirus 1 (SDRV1), was identified in four of 23 (17%) viscera pools. Phylogenetic analysis placed SDRV1 in the genus Alphanemrhavirus, which includes two recognized species that were identified in nematodes. Finally, a highly divergent rhabdovirus, Sodak rhabdovirus 2 (SDRV2), was identified in two of 23 (8.7%) big brown bats. Phylogenetic analysis placed SDRV2 as ancestral to the dimarhabdovirus supergroup and Lyssavirus. Intracranial inoculation of mouse pups with rhabdovirus-positive tissue homogenates failed to elicit clinical disease. Further research is needed to determine the zoonotic potential of these non-rabies rhabdoviruses.     

Retrospective Enhanced Bat Lyssavirus Surveillance in Germany between 2018–2020

Lyssaviruses are the causative agents for rabies, a zoonotic and fatal disease. Bats are the ancestral reservoir host for lyssaviruses, and at least three different lyssaviruses have been found in bats from Germany. Across Europe, novel lyssaviruses were identified in bats recently and occasional spillover infections in other mammals and human cases highlight their public health relevance. Here, we report the results from an enhanced passive bat rabies surveillance that encompasses samples without human contact that would not be tested under routine conditions. To this end, 1236 bat brain samples obtained between 2018 and 2020 were screened for lyssaviruses via several RT-qPCR assays. European bat lyssavirus type 1 (EBLV-1) was dominant, with 15 positives exclusively found in serotine bats (Eptesicus serotinus) from northern Germany. Additionally, when an archived set of bat samples that had tested negative for rabies by the FAT were screened in the process of assay validation, four samples tested EBLV-1 positive, including two detected in Pipistrellus pipistrellus. Subsequent phylogenetic analysis of 17 full genomes assigned all except one of these viruses to the A1 cluster of the EBLV-1a sub-lineage. Furthermore, we report here another Bokeloh bat lyssavirus (BBLV) infection in a Natterer’s bat (Myotis nattereri) found in Lower Saxony, the tenth reported case of this novel bat lyssavirus.     

Trends in national surveillance data for bat rabies in the United States: 2001-2009

Rabies remains an important public health concern in the United States, with most human cases associated with bat rabies virus variants. Cases of rabies virus (RV) infection in bats are widely distributed across the continental United States and elsewhere in the Americas. In this retrospective study, data on bats submitted to state laboratories for RV diagnosis between 2001 and 2009 were analyzed to investigate epidemiological trends in the United States. Season, region, and roosting habits were the primary risk factors of interest. During the study interval, more than 205,439 bats were submitted for RV diagnosis, and 6.7% of these bats were rabid. Increased odds of a submitted bat being rabid were associated with species that exhibit inconspicuous roosting habits, bats originating in the Southwest, and bats submitted for diagnosis during the fall. Periodic analysis of zoonotic disease surveillance is recommended to detect changes in trends regarding geographic distribution, seasonal fluctuations, and host associations; this is particularly necessary, as existing trends may be influenced by climate change or other emerging factors.     

Laboratory investigation of human deaths from vampire bat rabies in Peru.

In the spring of 1996, multiple cases of an acute febrile illness resulting in several deaths in remote locations in Peru were reported to the Centers for Disease Control and Prevention (CDC). The clinical syndromes for these cases included dysphagia and encephalitis. Because bat bites were a common occurrence in the affected areas, the initial clinical diagnosis was rabies. However, rabies was discounted primarily because of reported patient recovery. Samples of brain tissue from two of the fatal cases were received at CDC for laboratory confirmation of the rabies diagnosis. An extensive array of tests on the formalin-fixed tissues confirmed the presence of both rabies viral antigen and nucleic acid. The virus was shown to be most closely related to a vampire bat rabies isolate. These results indicate the importance of maintaining rabies in the differential diagnosis of acute febrile encephalitis, particularly in areas where exposure to vampire bats may occur.     

Effects of aerosolized rabies virus exposure on bats and mice

Between 1956 and 1977, 4 human cases of rabies virus infection were attributed to aerosolized rabies virus; however, little work has been done to address this topic since the late 1960s. Employing modern nebulization equipment coupled with serologic, cell culture, and molecular technology, we have continued the investigation into aerosolized rabies virus as a potential route of transmission. Laboratory mice and 2 species of bats were exposed, through aerosol, to 3 variants of rabies virus. All bats survived exposure to aerosolized rabies virus and produced rabies neutralizing antibody. Several mice died of rabies as a result of aerosol exposure. Antibody response was followed for 6 months before animals were given an intramuscular challenge of rabies virus. Poor protection from challenge was afforded in bats, despite the presence of neutralizing antibodies.     

Vampire Bat Rabies: Ecology,Epidemiology and Control

Extensive surveillance in bat populations in response to recent emerging diseases has revealed that this group of mammals acts as a reservoir for a large range of viruses. However, the oldest known association between a zoonotic virus and a bat is that between rabies virus and the vampire bat. Vampire bats are only found in Latin America and their unique method of obtaining nutrition, blood-feeding or haematophagy, has only evolved in the New World. The adaptations that enable blood-feeding also make the vampire bat highly effective at transmitting rabies virus. Whether the virus was present in pre-Columbian America or was introduced is much disputed, however, the introduction of Old World livestock and associated landscape modification, which continues to the present day, has enabled vampire bat populations to increase. This in turn has provided the conditions for rabies re-emergence to threaten both livestock and human populations as vampire bats target large mammals. This review considers the ecology of the vampire bat that make it such an efficient vector for rabies, the current status of vampire-transmitted rabies and the future prospects for spread by this virus and its control.     

Antigenic typing of Brazilian rabies virus samples isolated from animals and humans, 1989-2000

Animal and human rabies samples isolated between 1989 and 2000 were typified by means of a monoclonal antibody panel against the viral nucleoprotein. The panel had been previously established to study the molecular epidemiology of rabies virus in the Americas. Samples were isolated in the Diagnostic Laboratory of the Pasteur Institute and in other rabies diagnostic centers in Brazil. In addition to the fixed virus samples CVS-31/96-IP, preserved in mouse brain, and PV-BHK/97, preserved in cell culture, a total of 330 rabies virus samples were isolated from dogs, cats, cattle, horses, bats, sheep, goat, swine, foxes, marmosets, coati and humans. Six antigenic variants that were compatible with the pre-established monoclonal antibodies panel were defined: numbers 2 (dog), 3 (Desmodus rotundus), 4 (Tadarida brasiliensis), 5 (vampire bat from Venezuela), 6 (Lasiurus cinereus) and Lab (reacted to all used antibodies). Six unknown profiles, not compatible with the panel, were also found. Samples isolated from insectivore bats showed the greatest variability and the most commonly isolated variant was variant-3 (Desmodus rotundus). These findings may be related to the existence of multiple independent transmission cycles, involving different bat species.     

Recent Observations on Australian Bat Lyssavirus Tropism and Viral Entry

Australian bat lyssavirus (ABLV) is a recently emerged rhabdovirus of the genus lyssavirus considered endemic in Australian bat populations that causes a neurological disease in people indistinguishable from clinical rabies. There are two distinct variants of ABLV, one that circulates in frugivorous bats (genus Pteropus) and the other in insectivorous microbats (genus Saccolaimus). Three fatal human cases of ABLV infection have been reported, the most recent in 2013, and each manifested as acute encephalitis but with variable incubation periods. Importantly, two equine cases also arose recently in 2013, the first occurrence of ABLV in a species other than bats or humans. Similar to other rhabdoviruses, ABLV infects host cells through receptor-mediated endocytosis and subsequent pH-dependent fusion facilitated by its single fusogenic envelope glycoprotein (G). Recent studies have revealed that proposed rabies virus (RABV) receptors are not sufficient to permit ABLV entry into host cells and that the unknown receptor is broadly conserved among mammalian species. However, despite clear tropism differences between ABLV and RABV, the two viruses appear to utilize similar endocytic entry pathways. The recent human and horse infections highlight the importance of continued Australian public health awareness of this emerging pathogen.     

Rabies in France: an update

INTRODUCTION: In 1996, rabies was responsible for more than 35,000 deaths worldwide. Three cases of human rabies that had been contracted abroad were diagnosed in France during the same year. Cases notified in 1997 followed exposure outside the country. Fox, bat, and dog rabies are reviewed on the basis of the latest epidemiological data obtained in France. CURRENT KNOWLEDGE AND KEY POINTS: Two cases of fox rabies diagnosed in 1998 occurred at the border between France and Germany, thus preventing five French departments bordering Germany from being officially declared rabies-free in 1999. The campaigns for oral immunization of foxes that are led since 1986 are responsible for the decrease in rabies incidence. Though not well known, bat rabies is a reality in France, involving either European virus strains (five cases all over the country) or African virus strains that are carried along by imported tropical bats. Dogs rabies is also today an imported disease. FUTURE PROSPECTS AND PROJECTS: The decrease in risk for rabies has resulted from the conjunction of multiple efforts: extensive programs aimed at oral vaccination of foxes in France and its neighboring countries, efficient epidemiological survey, sanitary controls at borders, ban on importing tropical bats. Furthermore, recommendations for preventive pre-exposure immunization have recently been changed, leading to modifications of the French licensing form.     

Rabies in a nine-year-old child: The myth of the bite.

A nine-year-old boy died from rabies encephalitis caused by a rabies virus variant associated with insectivorous bats. The patient was most likely infected in the Laurentian Mountains of western Quebec, but neither the patient nor his parents remembered any direct contact with an animal. The diagnosis was made seven days after the start of symptoms. After examining the most recent cases of rabies in North America, it is obvious that rabies following bat exposure can occur without history of a documented bite. The present case report emphasizes that the general public and medical care providers need better information about the risks associated with exposure to bats.     

Rabies: relevance, prevention, and management in travel medicine

Rabies is a zoonotic viral disease, transmitted only in mammals. Terrestrial rabies, predominantly transmitted by dogs, is the most important rabies cycle threatening humans. The causative neurotropic virus is a negative-stranded RNA virus of the family Rhabdoviridae, genus Lyssavirus. This genus contains several rabies-related viruses. All variants are known or suspected to cause rabieslike diseases. Transmission occurs by the virus entering through the skin or the mucosa after bites, scratches, or preexisting injuries contaminated by the saliva of an infected mammal. Only 51 human rabies cases that have not been transmitted by animal bites are described.     

Confirmed rabies exposure during pregnancy: treatment with human rabies immune globulin and human diploid cell vaccine

A review of the literature shows 24 cases of pregnant human exposure to rabies virus through confirmed rabid animal bites. Historically, these patients received passive immunization with equine rabies immunoglobulin and/or purified vero cell vaccine or duck embryo vaccine. With the recent development of human-derived rabies vaccines, we report an additional case of human gestational rabies exposure, which was treated with human rabies immune globulin and human diploid cell vaccine.     

Variable evolutionary routes to host establishment across repeated rabies virus host shifts among bats

Determining the genetic pathways that viruses traverse to establish in new host species is crucial to predict the outcome of cross-species transmission but poorly understood for most host–virus systems. Using sequences encoding 78% of the rabies virus genome, we explored the extent, repeatability and dynamic outcome of evolution associated with multiple host shifts among New World bats. Episodic bursts of positive selection were detected in several viral proteins, including regions associated with host cell interaction and viral replication. Host shifts involved unique sets of substitutions, and few sites exhibited repeated evolution across adaptation to many bat species, suggesting diverse genetic determinants over host range. Combining these results with genetic reconstructions of the demographic histories of individual viral lineages revealed that although rabies viruses shared consistent three-stage processes of emergence in each new bat species, host shifts involving greater numbers of positively selected substitutions had longer delays between cross-species transmission and enzootic viral establishment. Our results point to multiple evolutionary routes to host establishment in a zoonotic RNA virus that may influence the speed of viral emergence.     

Immunology of Bats and Their Viruses: Challenges and Opportunities

Bats are reservoir hosts of several high-impact viruses that cause significant human diseases, including Nipah virus, Marburg virus and rabies virus. They also harbor many other viruses that are thought to have caused disease in humans after spillover into intermediate hosts, including SARS and MERS coronaviruses. As is usual with reservoir hosts, these viruses apparently cause little or no pathology in bats. Despite the importance of bats as reservoir hosts of zoonotic and potentially zoonotic agents, virtually nothing is known about the host/virus relationships; principally because few colonies of bats are available for experimental infections, a lack of reagents, methods and expertise for studying bat antiviral responses and immunology, and the difficulty of conducting meaningful field work. These challenges can be addressed, in part, with new technologies that are species-independent that can provide insight into the interactions of bats and viruses, which should clarify how the viruses persist in nature, and what risk factors might facilitate transmission to humans and livestock.