bRabies virus (RABV) maintenance in bats is not well understood. Big brown bats (Eptesicus fuscus), little brown bats (Myotis lucifugus), and Mexican free-tailed bats (Tadarida brasiliensis) are the most common bats species in the United States. These colonial bat species also have the most frequent contact with humans and domestic animals. However, the silver-haired bat (Lasionycteris noctivagans) RABV is associated with the majority of human rabies virus infections in the United States and Canada. This is of interest because silver-haired bats are more solitary bats with infrequent human interaction. Our goal was to determine the likelihood of a colonial bat species becoming infected with and transmitting a heterologous RABV. To ascertain the potential of heterologous RABV infection in colonial bat species, little brown bats were inoculated with a homologous RABV or one of two heterologous RABVs. Additionally, to determine if the route of exposure influenced the disease process, bats were inoculated either intramuscularly (i.m.) or subcutaneously (s.c.) with a homologous or heterologous RABV. Our results demonstrate that intramuscular inoculation results in a more rapid progression of disease onset, whereas the incubation time in bats inoculated s.c. is significantly longer. Additionally, cross protection was not consistently achieved in bats previously inoculated with a heterologous RABV following a challenge with a homologous RABV 6 months later. Finally, bats that developed rabies following s.c. inoculation were significantly more likely to shed virus in their saliva and demonstrated increased viral dissemination. In summary, bats inoculated via the s.c. route are more likely to shed virus, thus increasing the likelihood of transmission. Lyssavirus infections have been reported in numerous species of terrestrial and flying mammals (1, 2). Several regions of enzootic rabies virus (RABV) activity occur in raccoon, skunk, and fox populations within the continental United States. These enzootic foci are generally limited to homologous infections; e.g., raccoons are infected with a raccoon rabies virus variant (2). Despite less geographical isolation, chiropteran RABVs are also typically limited to their host species (3). However, RABV spillover into heterologous hosts does occur and has been implicated in the origin of raccoon-and skunk-adapted RABVs (4).Two of the most common species of bats in the continental Unites States are the big brown bat (Eptesicus fuscus) and the little brown bat (Myotis lucifugus) (5). These highly colonial species are adapted to living in both urban and rural areas. On the basis of data from public health rabies laboratories, big brown bats and little brown bats are the bat species most commonly submitted for rabies testing. The large number of submissions stems from human or domestic animal exposure (6). Despite frequent interaction, only three human rabies cases acquired in the United States have been associated with the little brown bat or big brown bat RABV since 1990 (Fox News)...

The study of a zoonotic disease requires an understanding of the disease incidence in animal reservoirs. Rabies incidence in bats submitted to diagnostic laboratories does not accurately reflect the true incidence in wild bat populations as a bias exists for testing bats that have been in contact with humans or pets. This article details the rabies incidence in two species of bats collected from natural settings without such bias. In this study, brain smears from 0.6% and 2.5% of wild-caught and apparently healthy Tadarida brasiliensis and Eptesicus fuscus, respectively, were positive for rabies virus (RV) antigen. Conversely, 92% of the grounded T. brasiliensis were positive for RV. Serology performed on captive colony and sick bats reveal an immune response to rabies. This work illustrates the complex interplay between immunity, disease state, and the conundrum of RV maintenance in bats.

Silver-haired bats, (Lasionycteris noctivagans) are semi-colonial, migratory tree bats that have infrequent contact with humans. Despite the species rarity, the L. noctivagans rabies variant is the most commonly reported rabies virus variant (RABV) in domestically acquired human rabies cases in the US. Unlike big brown bats (Eptesicus fuscus) and little brown bats (Myotis lucifugus), L. noctivagans are not considered true hibernators. It is unknown if RABV can overwinter in hibernating L. noctivagans or is only maintained in members of this taxa that migrate to warmer climates. To better understand RABV overwintering in this species, L. noctivagans were inoculated intramuscularly with either a homologous RABV (L. noctivagans Virus 1) or one of two heterologous RABV (Eptesicus fuscus Virus 2 and Myotis lucifugus Virus 1). Five days following inoculation, L. noctivagans were placed in a hibernation chamber for 6 weeks. Our results demonstrate that rabies virus can overwinter in L. noctivagans yet the incubation period was extended 6 weeks when compared to bats maintained at ambient temperatures. Additionally, we found that the longer the incubation period, the greater the viral dissemination to the salivary glands. Similar to our previous studies, L. noctivagans were most susceptible to a homologous variant. In summary, we found that RABV incubation is extended following a subcutaneous exposure or maintenance in hibernation and longer incubation times increase dissemination and potential for transmission.