Immune System Modulation and Viral Persistence in Bats: Understanding Viral Spillover

Subudhi, Sonu; Rapin, Noreen; Misra, Vikram

Pathogen shedding by bats is a complex phenomenon regulated by host antiviral defenses and viral factors. A host's defenses attempt to control virus infection but viruses have evolved mechanisms to counteract them [13] . When the host defenses are suppressed, or if the virus is able to circumvent the host immune system, virus replication is enhanced, leading to an increase in virus shedding. The route of shedding is highly dependent on the tissue in which the virus replication occurs. For example, increased replication in the kidney would lead the bat to shed the virus in urine, whereas intestinal replication would result in dissemination through feces. Therefore, it becomes important to study what factors might be responsible for decreasing the host defense or factors that allow the virus to circumvent host immune response. But before exploring factors affecting virus-host interactions, it is imperative to understand the viruses present in bats and the bat immune defenses. In 2013-2014, bat immunology was at a nascent stage and Schountz and Baker et al. [14, 15] had summarized the preliminary knowledge about it in their reviews. In 2017, Schountz et al. [16] again reviewed bat immunology but the article also laid out gaps in our understanding of host pathogen interactions in bats. Here, we include more recent advances in characterizing the bat immune system including a possible link between the evolution of flight in bats and viral persistence. Following that section, we discuss the factors identified so far that upset the balanced bat-virus relationship, potentially leading to the spillover of viruses.