Interrogating stress and viral shedding in a migratory bat model

Bats harbor many zoonotic viruses, including both genera of coronaviruses (CoVs) pathogenic in humans (α- and β- CoVs). Limited evidence to-date suggests that periods of active infection in bats—and thus opportunities to transmit zoonotic viruses to humans—are driven by energetically demanding periods that modulate immune tolerance of infection and facilitate viral replication and shedding. However, such work has largely ignored immune mechanisms and has focused primarily on reproductive and nutritional stress. This project will combine field studies and in vitro analyses to test long-distance migration in bats as a driver of CoV infection and shedding.

We will focus on Mexican free-tailed bats (Tadarida brasiliensis), a common and widespread migratory bat species in North America for which we and others have detected CoVs similar to HCoV-229E and that are susceptible to SARS-CoV-2. In Aim 1, we will sample T. brasiliensis at monthly intervals at our established study site in western Oklahoma, capturing energetically demanding periods of spring migration from Mexico, birth and lactation, and fall migration back to Mexico. We will characterize CoV diversity and infection status in saliva and fecal samples using RT-PCR followed by Sanger sequencing and will attempt to isolate naturally occuring bat CoVs. We will also quantify stress physiology through fecal cortisol and ratios of neutrophils to lymphocytes in blood, followed by generalized additive models to assess seasonality in physiological metrics and viral infection as well as to test how bat physiology relates to viral shedding.

In Aim 2, we will collect lung and intestine from male and female T. brasiliensis bats and use our established protocols to develop new primary and immortalized cell lines, expanding the limited in vitro resources currently available for this bat species from an existing lung epithelial cell line. We will then test virus susceptibility and permissivity by infecting these new cell lines with HCoV 229E, SARS-CoV-2, and MERS-CoV; if isolation of natural bat CoVs is successful, we will also include infections with these viruses. Viral replication will be assessed by qRT-PCR, immunofluorescence microscopy, and TCID50 assays. In Aim 3, we will use our novel T. brasiliensis cell lines to run factorial viral and cortisol challenge experiments to mimic the stressors observed in the field and their impacts on virus replication (i.e., HCoV 229E, SARS-CoV-2, and MERS-CoV as well as any CoVs we isolate here).

Viral and cortisol challenges will be followed by global gene expression analyses via RNA-Seq to discover the response of bat cells to field-relevant cortisol concentrations in the face of CoV infection. This project will thus characterize relationships between the physiological demands of migration and CoV infection in wild bats and in vitro systems, establishing a pipeline for studying how stressors affect bat-borne zoonoses.

Grant Number: 1R21AI190246-01
NIH Institute/Center: NIH
Principal Investigator: Daniel Becker