Experimental Lagos bat virus infection in straw-colored fruit bats: A suitable model for bat rabies in a natural reservoir species

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 10(0.1) to 10(4.1) median tissue culture infectious dose (TCID50). More bats died due to the development of rabies after the middle dose (10(2.1) TCID50, 4/4 bats) than after lower (10(1.1), 2/4; 10(1.1), 2/4) or higher (10(3.1), 2/4; 10(4.1), 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 10(2.1) 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. Author summary Rabies is a fatal neurologic disease affecting people and animals. Rabies is caused by infection with a virus of the genus Lyssavirus. People usually get infected from dog bites, but bats are an increasingly important source of the disease. To better understand the biology of rabies in bats, we developed a laboratory model to study the disease in bats under controlled circumstances. For this model we used Lagos bat virus in straw-colored fruit bats and, as part of its development, we wanted to know the best virus dose to use to cause rabies. Therefore, we compared the outcomes of five different virus doses injected into the muscle of the bats. The best dose for our model was the middle dose, which caused rabies more frequently than either the highest or the lowest doses. The higher doses more frequently resulted in the development of an anti-viral immune response which appeared to protect against disease, while bats with low doses also often failed to develop disease. The virus dose thus followed the Goldilocks principle, with the middle dose being just right.