By Carol A. Kemper, MD, FACP
Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center
SOURCE: Chandler JC, Bevins SN, Ellis JW, et al. SARS-CoV-2 exposure in wild white-tailed deer (Odocoileus virginianus). Proc Natl Acad Sci USA 2021;118:e2114828118.
The U.S. Department of Agriculture/Animal and Plant Health Inspection Service (APHIS)/Wildlife Services National Disease Program conducts routine surveillance for a variety of bacterial, viral, and parasitic diseases in the plant and animal worlds. These are the same people who put Mediterranean fruit fly traps in my mandarin tree and bleed sentinel chickens every two weeks from March through October looking for West Nile virus and other mosquito-borne diseases. In 2021, APHIS began examining the prevalence of SARS-CoV-2 antibodies in white-tailed deer throughout several Northeastern states. A total of 624 pre- and post-COVID-19 pandemic serum samples were randomly selected from specimens obtained for disease surveillance in 2011-2021 for other disease entities (e.g., bovine tuberculosis and chronic wasting disease).
Unexpectedly, 152 of 280 samples from 2021 and three of 100 samples from 2020 were positive for SARS-CoV-2 antibodies. None of the specimens from 2011-2018 and only one from 2019 was positive. To evaluate the possibility of cross-reaction with another cervid SARS-like virus, a subset of specimens was tested further using a viral neutralization assay (NA). NA confirmed the results were highly concordant, with the exception of the single positive assay from 2019, suspected to be falsely positive on initial testing. Interestingly, most of the 2020 specimens were obtained in January through March of that year, and all three positive 2020 specimens were collected in January. If true, then cross-species infection occurred early in the pandemic. Because the specimens collected were described as “opportunistic,” dependent on when a deer was culled or a specimen collected, true seroprevalence over time cannot be derived. Positive specimens were collected, in descending order of frequency, from Michigan (67%), Pennsylvania (31%), New York (19%), and Illinois (7%). However, deer from half the represented counties were negative, and most positive deer were clustered within a few adjacent counties.
COVID-19 has become a North American zoonosis endemic in the Northeastern white-tailed deer population. Whether it causes symptomatic infection is unclear, but the authors suspected most infections are subclinical, with viral shedding in nasal secretions and feces. Now that infection has become established in this animal group, it likely will spread easily, as demonstrated by the frequency of positive results in 2021. Animal reservoirs, such as white-tailed deer, provide a source of persistent circulating infection, which can lead to the emergence of different strains, and even the possibility of cross-species gene reassortment. It also means COVID-19 can never be eradicated as a human pathogen.
COVID-19 has become a North American zoonosis endemic in the Northeastern white-tailed deer population. Whether it causes symptomatic infection is unclear, but most infections likely are subclinical, with viral shedding in nasal secretions and feces. Now that infection has become established in this animal group, it likely will spread easily.
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