Uncovering mechanisms that underpin bat virus virulence

Project Summary Bats are reservoir hosts for zoonoses that cause the highest case fatality rates documented in humans, including rabies and related lyssaviruses, Hendra and Nipah henipaviruses, Ebola and Marburg filoviruses, and SARS and MERS coronaviruses. Bats exhibit limited disease upon infection with these viruses that cause extreme pathology in other mammals, likely due to robust and rapid innate and cell-mediated immune defenses, coupled with hyper-efficient mechanisms of DNA damage repair and dampened inflammatory pathways. Recent theoretical work in our lab demonstrates how these unique features of bat immunology and physiology—chiefly, constitutive antiviral immunity and resilience to inflammation that confers tolerance to immunopathology—should select for the evolution of high virus growth rates that, while avirulent to bats, are likely to cause pathology following spillover to non-bat, including human, hosts. Here, we seek to explicitly test the predictions of our theoretical model by carrying out experimental evolution of vesicular stomatitis virus (VSV) in bat cell cultures that span a range of both (Aim 1) constitutive antiviral and (Aim 2) inflammation tolerant phenotypes. Under Aim 1, we examine variation in VSV growth rate evolution and the rate of molecular evolution following serial passage of virus across a suite of Pteropus alecto bat cell lines that exhibit both intact (wildtype) and deficient (CRISPR knock-outs) antiviral immune functions. Under Aim 2, we leverage our lab’s unique system of primary bat fibroblast cell lines derived from related species spanning a range of longevities to evaluate whether cells derived from longer-lived species that demonstrate resilience to aging-related stressors also exhibit heightened tolerance of virus infection. We then compare VSV evolution following serial passage across cell lines that demonstrate variable resilience to aging-related stressors in vitro. We hypothesize that antiinflammatory properties in bat cells which confer resilience to aging stressors may also facilitate virus tolerance by limiting immunopathology and—by extension—drive the evolution of high growth rate viruses likely to generate pathology in non-bat hosts. Ultimately, we offer an explicit empirical test of the hypothesized mechanisms underpinning the extreme virulence of bat virus zoonoses.