Abstract
Understanding the factors underpinning emergence and reemergence of virulent viral zoonoses is of critical importance. In particular, bats are known to host virulent zoonotic viruses without experiencing disease. Previous work suggests that bats’ viral hosting capacities may partially result from uniquely constitutive immune capabilities, but the impact of these defenses on viral dynamics within-host has yet to be explored. We carried out viral infectivity assays on bat cell lines expressing induced and constitutive immune phenotypes, then developed a theoretical model of our in vitro system, which we fit to empirical data to estimate rates of within-host viral propagation and assumption of antiviral defenses. Persistent viral infections established under both induced and constitutive immune assumptions, but constitutive immunity produced consistently faster within-host viral propagation rates. Faster-replicating viruses evolved in bat hosts possessing perpetually antiviral immune capabilities are likely to exhibit enhanced virulence following emergence into novel hosts lacking constitutive immunity.