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

Subudhi, Sonu; Rapin, Noreen; Misra, Vikram

Over the past few years, the interest in bat research has increased because of the range of viruses that they harbor and the potential of spillover to humans and other vertebrates [1] . In some instances, there is direct evidence that viruses have spilled over from bats to other vertebrates. For example, Nipah virus spilled over from bats to humans and pigs leading to outbreaks in Southeast Asia and Hendra virus continues to spillover into horses and humans in Australia [2] [3] [4] [5] [6] . In other instances, the evidence of virus spillover from bats is circumstantial. For example, in case of ebolaviruses, serological evidence and the detection of viruses related to the ebolaviruses in bats [7, 8] suggests that they are reservoirs of the virus. Recent discoveries of filoviruses in bats of China and Sierra Leone have further bolstered this claim [9, 10] . However, viruses linked to specific Ebola virus disease (EVD) epidemics have not yet been detected in bats. Although bats harbor many diverse viruses, their spillover to other animals is extremely rare [11] . One of the reasons is that for a spillover event to take place several factors such as pathogen shedding, environmental conditions, pathogen persistence in environment, and recipient host susceptibility, should all be conducive to transmission. This would result in the "perfect storm" required for spillover. A review by Plowright et al. [12] describes the factors that could lead to such a perfect storm. Here, we focus on one of the initial events affecting this spillover, i.e., an increase in pathogen shedding.