Illustration by Laura Alexander Bats play host to some of the gnarliest, deadliest viruses known today, including those that cause Ebola, Marburg, SARS and MERS. So what gives? Are these fuzzy flying mammals special in some way in their propensity to produce zoonotic pathogens that infect us humans? There’s a growing consensus that the answer to this question is almost certainly “yes!”, but what is it that makes bats special viral vessels? This week, Cara Brook, a Miller Postdoctoral Fellow at UC Berkeley, shared her research seeking to answer this question. Cara started with some basic bat biology that helps explain why they may be so special. Bats are among the longest-lived mammals for their size, are highly gregarious, do that whole flying thing, and have some curious immune functions. Among these are partial resistance mechanisms to viruses that help prevent pathology such as inflammation that is normally associated with viral infection. Even more unique is their constitutive expression of IFN-, an anti-viral cytokine. This suggests that bats are better equipped than other mammals to fight off viral infections, and do so with minimal associated pathology! Seasonality in seroprevalence and viral shedding rates among bats suggests that there may be more to these anti-viral immune responses, though. Cara’s been conducting research in Madagascar in an attempt to identify the precise drivers of this seasonality. She’s found that female fruit bats in Madagascar in particular have increased viral titers during gestation and lactation, perhaps implying that female individuals are sacrificing resources that would normally be devoted to immunity to instead raise some bat babies. Some additional modeling work suggests that maternal immunity passed on to those same bat babies that wanes following the first year of life is also playing an important role in observed seroprevalence patterns. This result was dependent on fitting age-structured models to seroprevalence data from bats of different ages. How do you determine how old a bat is you might ask? Cara, the chiropteran tooth fairy, explained that age can be determined from an extracted bat tooth, and that this simple dental procedure does not affect long-term bat survival or fitness. Moving from the dental to the molecular, Cara next told us about her within-host research that seeks to explain how bats manage the dance between viral exposure, a constitutive viral immune response, and immunopathology. She’s using in vitro experiments and within-host, cell-based models to explore how viruses move between cells and between bats. Cara told us that these results suggest that bats’ constitutive immunity causes higher replication rates of viruses within individuals. It was a tour-de-force of field, modeling, and molecular work and taught everyone here at Berkeley EEID a lot about bats as reservoirs for emerging infectious diseases! Writing by Chris Hoover
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February 2020
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