Serological survey for rabies in serum samples from vampire bats (Desmodus rotundus) in Botucatu region, SP, Brazil

Serological Surveillance of Rabies in Free-Range and Captive Common Vampire Bats Desmodus rotundus

The control of vampire bat rabies (VBR) in Brazil is based on the culling of Desmodus rotundus and the surveillance of outbreaks caused by D. rotundus in cattle and humans in addition to vaccination of susceptible livestock. The detection of anti-rabies antibodies in vampire bats indicates exposure to the rabies virus, and several studies have reported an increase of these antibodies following experimental infection. However, the dynamics of anti-rabies antibodies in natural populations of D. rotundus remains poorly understood. In this study, we took advantage of recent outbreaks of VBR among livestock in the Sao Paulo region of Brazil to test whether seroprevalence in D. rotundus reflects the incidence of rabies in nearby livestock populations. Sixty-four D. rotundus were captured during and after outbreaks from roost located in municipalities belonging to three regions with different incidences of rabies in herbivores. Sixteen seropositive bats were then kept in captivity for up to 120 days, and their antibodies and virus levels were quantified at different time points using the rapid fluorescent focus inhibition test (RFFIT). Antibody titers were associated with the occurrence of ongoing outbreak, with a higher proportion of bats showing titer >0.5 IU/ml in the region with a recent outbreak. However, low titers were still detected in bats from regions reporting the last outbreak of rabies at least 3 years prior to sampling. This study suggests that serological surveillance of rabies in vampire bats can be used as a tool to evaluate risk of outbreaks in at risk populations of cattle and human.

Rabies virus-neutralising antibodies in healthy, unvaccinated individuals: What do they mean for rabies epidemiology?

Rabies has been a widely feared disease for thousands of years, with records of rabid dogs as early as ancient Egyptian and Mesopotamian texts. The reputation of rabies as being inevitably fatal, together with its ability to affect all mammalian species, contributes to the fear surrounding this disease. However, the widely held view that exposure to the rabies virus is always fatal has been repeatedly challenged. Although survival following clinical infection in humans has only been recorded on a handful of occasions, a number of studies have reported detection of rabies-specific antibodies in the sera of humans, domestic animals, and wildlife that are apparently healthy and unvaccinated. These 'seropositive' individuals provide possible evidence of exposure to the rabies virus that has not led to fatal disease. However, the variability in methods of detecting these antibodies and the difficulties of interpreting serology tests have contributed to an unclear picture of their importance. In this review, we consider the evidence for rabies-specific antibodies in healthy, unvaccinated individuals as indicators of nonlethal rabies exposure and the potential implications of this for rabies epidemiology. Our findings indicate that whilst there is substantial evidence that nonlethal rabies exposure does occur, serology studies that do not use appropriate controls and cutoffs are unlikely to provide an accurate estimate of the true prevalence of nonlethal rabies exposure.

The common vampire bat Desmodus rotundus (Chiroptera: Phyllostomidae) and the transmission of the rabies virus to livestock: A contact network approach and recommendations for surveillance and control

The importance of the common vampire bat Desmodus rotundus for the transmission of the rabies virus does not lie solely in its ability to transmit this disease to other mammals, but also in its capacity to adapt to environmental and climatic changes, granting them a wide geographical distribution. Control of this disease is currently based on culling of the vampire bat and vaccination of the livestock. A transmission model incorporating geographic and behavioral determinants of the vampire bat was proposed to direct and optimize the epidemiological surveillance and control of livestock rabies. This model was built using a bimodal network connecting 260 vampire bat roosts among themselves (roost-roost-network) and with 1557 farms (roost-farm network) in eastern Sao Paulo State, Brazil. These roosts were grouped in 9 communities, some very interconnected, and some not and the farms were grouped in 14 communities. From 2013 to 2017, 44 livestock rabies outbreaks occurred in the area, circulating among the farm communities during the entire period, with possible introductions from neighboring areas. Based on the network and environment parameters, it was possible to reasonably predict both the roosts' occupation type (harem, bachelor, overnight and empty) and livestock rabies outbreak occurrence. The network approach brings light to the importance of phylogenetic studies of bats and rabies virus. Finally, the understanding of the interactions between bats and their feeding sources, influenced by the environment, allows to establish more precise surveillance and control measures and, ultimately, with a lower cost-benefit ratio of these actions.

Rabies - epidemiology, pathogenesis, public health concerns and advances in diagnosis and control: a comprehensive review

Rabies is a zoonotic, fatal and progressive neurological infection caused by rabies virus of the genus Lyssavirus and family Rhabdoviridae. It affects all warm-blooded animals and the disease is prevalent throughout the world and endemic in many countries except in Islands like Australia and Antarctica. Over 60,000 peoples die every year due to rabies, while approximately 15 million people receive rabies post-exposure prophylaxis (PEP) annually. Bite of rabid animals and saliva of infected host are mainly responsible for transmission and wildlife like raccoons, skunks, bats and foxes are main reservoirs for rabies. The incubation period is highly variable from 2 weeks to 6 years (avg. 2-3 months). Though severe neurologic signs and fatal outcome, neuropathological lesions are relatively mild. Rabies virus exploits various mechanisms to evade the host immune responses. Being a major zoonosis, precise and rapid diagnosis is important for early treatment and effective prevention and control measures. Traditional rapid Seller's staining and histopathological methods are still in use for diagnosis of rabies. Direct immunofluoroscent test (dFAT) is gold standard test and most commonly recommended for diagnosis of rabies in fresh brain tissues of dogs by both OIE and WHO. Mouse inoculation test (MIT) and polymerase chain reaction (PCR) are superior and used for routine diagnosis. Vaccination with live attenuated or inactivated viruses, DNA and recombinant vaccines can be done in endemic areas. This review describes in detail about epidemiology, transmission, pathogenesis, advances in diagnosis, vaccination and therapeutic approaches along with appropriate prevention and control strategies.

Spatial expansions and travelling waves of rabies in vampire bats

A major obstacle to anticipating the cross-species transmission of zoonotic diseases and developing novel strategies for their control is the scarcity of data informing how these pathogens circulate within natural reservoir populations. Vampire bats are the primary reservoir of rabies in Latin America, where the disease remains among the most important viral zoonoses affecting humans and livestock. Unpredictable spatiotemporal dynamics of rabies within bat populations have precluded anticipation of outbreaks and undermined widespread bat culling programs. By analysing 1146 vampire bat-transmitted rabies (VBR) outbreaks in livestock across 12 years in Peru, we demonstrate that viral expansions into historically uninfected zones have doubled the recent burden of VBR. Viral expansions are geographically widespread, but severely constrained by high elevation peaks in the Andes mountains. Within Andean valleys, invasions form wavefronts that are advancing towards large, unvaccinated livestock populations that are heavily bitten by bats, which together will fuel high transmission and mortality. Using spatial models, we forecast the pathways of ongoing VBR epizootics across heterogeneous landscapes. These results directly inform vaccination strategies to mitigate impending viral emergence, reveal VBR as an emerging rather than an enzootic disease and create opportunities to test novel interventions to manage viruses in bat reservoirs.

Rabies surveillance in bats in Northwestern State of São Paulo

Introduction Rabies is an important zoonosis that occurs in mammals, with bats acting as Lyssavirus reservoirs in urban, rural and natural areas. Rabies cases in bats have been recorded primarily in urban areas in Northwestern State of São Paulo since 1998. This study investigated the circulation of rabies virus by seeking to identify the virus in the brain in several species of bats in this region and by measuring rabies-virus neutralizing antibody levels in the hematophagous bat Desmodus rotundus. Methods From 2008 to 2012, 1,490 bat brain samples were sent to the Universidade Estadual Paulista (UNESP) Rabies Laboratory in Araçatuba, and 125 serum samples from vampire bats that were captured in this geographical region were analyzed. Results Rabies virus was detected in the brains of 26 (2%) of 1,314 non-hematophagous bats using the fluorescent antibody test (FAT) and the mouse inoculation test (MIT). None of the 176 hematophagous bat samples were positive for rabies virus when a virus detection test was utilized. Out of 125 vampire bat serum samples, 9 (7%) had levels of rabies virus neutralization antibodies (RVNAs) that were higher than 0.5IU/mL; 65% (81/125) had titers between 0.10IU/mL and 0.5IU/mL; and 28% (35/125) were negative for RVNAs using the simplified fluorescent inhibition microtest (SFIMT) in BHK21 cells. The observed positivity rate (1.7%) was higher than the average positivity rate of 1.3% that was previously found in this region. Conclusions The high percentage of vampire bats with neutralizing antibodies suggests that recent rabies virus exposure has occurred, indicating the necessity of surveillance measures in nearby regions that are at risk to avoid diffusion of the rabies virus and possible rabies occurrences.

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.

Desmodus rotundus (Mammalia: Chiroptera) on the southern coast of Rio de Janeiro state, Brazil

Since the 1990s, attacks by hematophagous bats on humans and domestic animals have been reported both on the continent and on the islands on the southern coast of Rio de Janeiro state. The density of vampire bats was investigated based on percentage of captures during control of Desmodus rotundus samplings and during bat diversity research. In the present work, 203 individuals of D. rotundus were captured from 1993 to 2009, which corresponds to 11.88% of all bat captures carried out for species control in local villages and 1.58% of all captures in faunistic inventories. The density of D. rotundus is high even on the recently occupied islands where domestic animals have been introduced. It is probable that this species dispersed from the continent to the islands due to the introduction of domestic animals.