Study population and setting
To investigate whether wild bats are susceptible to SARS-CoV-2 infection, big brown bats (Eptesicus fuscus; n = 16) were collected from local human residences in Waushara County, Wisconsin in winter 2019-2020 and allowed to acclimate and quarantine for over 30 days prior to the start of the study. Seven pairs of bats were co-housed in mesh cages and one bat from each pair was inoculated orally and nasally with 1×10^5 50% tissue culture infective dose of SARS-CoV-2. The paired bat served as a direct contact for the inoculated bat. An eighth pair of bats served as a control, with both bats receiving a placebo infusion. Bats were monitored twice daily for clinical signs of infection and once daily for weight loss and for collection of oropharyngeal and rectal swabs. Pairs of bats from one cage were euthanized on day post-inoculation (DPI) 6, 12, and 20 for histopathological and virological analyses of tissues. Swabs and tissue samples were tested for the presence of SARS-CoV-2 RNA using quantitative real-time PCR targeting nucleoprotein. In situ hybridization targeting the SARS-CoV-2 spike protein was performed to test for the presence of virus in tissues. Antibodies (IgM and IgG) against SARS-CoV-2 spike protein in bat serum samples were tested using ELISA; sera from 10 big brown bats held at the facility for other experimental studies served as negative controls for antibody assays.
Summary of Main Findings
Prior to inoculation, 5/16 (31%) bats tested positive for an alphacoronavirus in feces (unrelated to SARS-CoV-2, a betacoronavirus). Bats showed no clinical signs of infection or weight loss over the 20 days of the study. While SARS-CoV-2 RNA was detected in oral swabs from 5/16 bats on DPI 0 (1 inoculated, 4 direct contact), no evidence of RNA shedding in feces was detected on DPI 0 and none of the remaining swabs collected through DPI 20 were positive for SARS-CoV-2 RNA. There was no evidence of virus in tissues collected from euthanized bats on DPI 6, 12, and 20 based on in situ hybridization and PCR (n = 8, 3 inoculated, 3 direct contact, and 2 controls); histopathology in lungs and other tissues was consistent with the euthanasia procedure and not with SARS-CoV-2 infection. There was also no evidence of significantly higher IgM or IgG antibodies in sera collected from any of the 16 bats above the negative controls.
Bats were tested for the presence of coronaviruses in feces prior to the start of the study.
Some bats had evidence of alphacoronavirus infections, but there does not appear to be any evidence of cross-reactivity to antibodies for the different coronavirus lineages, suggesting that these infections would not change bat susceptibility to SARS-CoV-2.
This study represents only the second experimental infection of a bat species with SARS-CoV-2 and the first for an insectivorous bat. The results validate predictions (https://www.pnas.org/cgi/doi/10.1073/pnas.2010146117) that this Eptesicus fuscus was unlikely to be a host due to the poor binding potential of its ACE2 receptor to the SARS-CoV-2 spike protein. However, the results contrast with another study (https://www.biorxiv.org/content/10.1101/2020.05.22.111344v3) that predicted Eptesicus fuscus to be a likely host of betacoronaviruses based on ecological traits and other viral infections.
This review was posted on: 4 February 2021