Study population and setting
To assess the susceptibility of white-tailed deer (Odocoileus virginianus) to SARS-CoV-2 infection, the authors performed experimental infections of deer cells and live animals. Entry of SARS-CoV-2 into cultured deer lung cells was assessed using an immunofluorescence assay targeting the SARS-CoV-2 nucleoprotein. In vivo infection of deer was evaluated using six-week-old fawns (n = 6) from a breeding herd in Ames, Iowa. Animals were raised in captivity and allowed to acclimate to the biosafety facility for two weeks prior to the start of the experiment. Four animals were inoculated intranasally with 10^6.3 50% tissue culture infective dose of SARS-CoV-2. The two remaining fawns were used as naïve controls housed in the same room to test the potential for indirect viral transmission between deer. Animals were monitored for clinical signs and changes in body temperature. Nasal and rectal swabs were collected between DPI 0 and 21; blood serum and buffy coat samples were collected at DPI 0, 7, 14, and 21. All samples were tested for viral RNA via real-time reverse transcription PCR and for infectious virus via culture on Vero E6 cells. Serum samples were tested reactive and neutralizing antibodies using Luminex and virus neutralization assays, respectively, targeting antibodies against the SARS-CoV-2 nucleoprotein and spike receptor binding domain.
Summary of Main Findings
Deer lung cells supported SARS-CoV-2 virus entry 24 hours post-inoculation and virus replication for up to 3 days. None of the animals showed any clinical signs of infection, though 3 out of 4 inoculated animals had slightly elevated body temperatures between DPI 1 and 3; body temperatures remained within the normal range in indirect contact animals. Viral RNA was detected in consistently in nasal secretions of inoculated and indirect contact animals between DPI 2 and 21; detection was inconsistent in rectal swabs. No viremia was detected in blood serum or buffy coat samples. Infectious virus was detected in nasal swabs between DPI 2 and 5 from inoculated animals and between DPI 2 and 7 from indirect contact animals. Infectious virus was only detected in fecal swabs from inoculated animals at 1 DPI. Inoculated and indirect contact animals produced reactive and neutralizing antibodies against SARS-CoV-2 N and spike RBD as early as 7 DPI, with increasing antibody titers at 14 and 21 DPI. A single inoculated animal died at DPI 8 from intestinal perforation unrelated to the experiment; the remaining 5 animals were sacrificed at 21 DPI. No gross lesions were observed in any necropsied tissues. SARS-CoV-2 RNA was detected in necropsied multiple upper respiratory tissues, spleen, and lymph nodes via PCR and in situ hybridization, but no infectious virus was detectable.
The experimental design tested the potential for indirect transmission between deer using a plexiglass barrier to prevent nose-to-nose contact between inoculated and naïve animals.
The study used a very small number of individuals, and the animals were all of uniform age and from the same source population. Thus, the results may not be generalizable to all white-tailed deer populations. The animals were also not tested for concurrent or past infection with other coronaviruses that might affect susceptibility to infection or serological tests. The authors were unable to detect infectious virus in any of the tissues sampled from necropsied animals at 8 and 21 DPI. Testing for infectious virus in tissues at additional timepoints would be necessary to find the active sites of virus replication.
Previous studies have shown that the ACE2 receptors of white-tailed deer and other deer and ruminants are highly similar to the human version (see https://doi.org/10.1073/pnas.2010146117), so it was assumed that deer would be susceptible to SARS-CoV-2 infection. White-tailed deer frequently live nearby humans in suburban areas in North America, are frequently hunted, and can be farmed, though not extensively. Due to this interface with humans, there was concern that transmission of SARS-CoV-2 from humans could establish virus circulation in wild or farmed deer populations. This is the first study to show that SARS-CoV-2 can infect and be transmitted by a deer species.
This review was posted on: 19 February 2021