Abstract
Rabies is a fatal neurologic disease caused by lyssavirus infection. Bats are important natural reservoir hosts of various lyssaviruses that can be transmitted to people. The epidemiology and pathogenesis of rabies in bats are poorly understood, making it difficult to prevent zoonotic transmission. To further our understanding of lyssavirus pathogenesis in a natural bat host, an experimental model using straw-colored fruit bats (Eidolon helvum) and Lagos bat virus, an endemic lyssavirus in this species, was developed. To determine the lowest viral dose resulting in 100% productive infection, bats in five groups (four bats per group) were inoculated intramuscularly with one of five doses, ranging from 100.1 to 104.1 median tissue culture infectious dose (TCID50). More bats died due to the development of rabies after the middle dose (102.1 TCID50, 4/4 bats) than after lower (101.1, 2/4; 101.1, 2/4) or higher (103.1, 2/4; 104.1, 2/4) doses of virus. In the two highest dose groups, 4/8 bats developed rabies. Of those bats that remained healthy 3/4 bats seroconverted, suggesting that high antigen loads can trigger a strong immune response that abrogates a productive infection. In contrast, in the two lowest dose groups, 3/8 bats developed rabies, 1/8 remained healthy and seroconverted and 4/8 bats remained healthy and did not seroconvert, suggesting these doses are too low to reliably induce infection. The main lesion in all clinically affected bats was meningoencephalitis associated with lyssavirus-positive neurons. Lyssavirus antigen was detected in tongue epithelium (5/11 infected bats) rather than in salivary gland epithelium (0/11), suggesting viral excretion via the tongue. Thus, intramuscular inoculation of 102.1 TCID50 of Lagos bat virus into straw-colored fruit bats is a suitable model for lyssavirus associated bat rabies in a natural reservoir host, and can help with the investigation of lyssavirus infection dynamics in bats.
Highlights
Rabies is an almost invariably fatal disease caused by rabies virus (RABV) or any other member of the Lyssavirus genus [1,2]
Disease causation was confirmed as being Lagos bat virus (LBV) infection by positive reverse transcription quantitative PCR (RT-qPCR), rabies tissue culture infection test (RTCIT), fluorescent antibody test (FAT), and immunohistochemical (IHC) examination of their brains
Day of death post inoculation due to LBV infection ranged from 7 to 17, with one outlier from the 100.1 TCID50 group, that died on day 61 pi (Fig 1)
Summary
Rabies is an almost invariably fatal disease caused by rabies virus (RABV) or any other member of the Lyssavirus genus (family: Rhabdoviridae, order: Mononegavirales) [1,2]. Experimental infections in bats have been performed mainly with four lyssaviruses: RABV, Australian bat lyssavirus, and European bat lyssaviruses 1 and 2 [49]. An important limiting factor in this previous bat-lyssavirus research is that oral excretion of virus was rarely observed in experimentally-infected bats making it difficult to test the hypothesis that bats are able to survive a productive lyssavirus infection [24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46]. The rare observation of oral excretion suggests experimental models for natural lyssavirus infections in bats need to be improved
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