A new study accepted for publication in the journal Transboundary and Emerging Diseases assesses the potential exposure of U.K. deer to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) since studies have shown the spill-over of SARS-CoV-2 infections to the Northern American white-tailed deer. If there is a spill-over, wild deer species can act as reservoirs of SARS-CoV-2 with the possibility of the emergence of new variants.
Study: Screening of wild deer populations for exposure to SARS-CoV-2 in the United Kingdom, 2020-2021. Image Credit: Mark Cane / Shutterstock
Evidence from North America
The white-tailed deer from Northern America have been found to shed the SARS-CoV-2 virus up to 5 days after being infected. Viral shedding correlates with a likelihood of transmission to deer. Furthermore, infection elicits an immune response and the production of neutralizing antibodies.
SARS-CoV-2 RNA has been detected in 36% of free-ranging white-tailed deer in multiple locations within Ohio from January-March 2021. There is evidence of sustained SARS-CoV-2 transmission within this deer population. Three different SARS-CoV-2 lineages have been detected in these deer populations projecting the possibility of multiple reverse zoonosis events.
A low SARS-CoV-2 prevalence was detected in white-tailed deer from Québec, Canada. Anti-SARS-CoV-2 antibodies have been observed in deer populations from Texas, Michigan, Pennsylvania, Illinois, New Jersey, and New York. These studies have looked at seroprevalence i.e., the presence of neutralizing antibodies in serum samples and a surrogate virus neutralization test (sVNT).
Deer to deer transmission has been observed in a captive cervid facility in Texas, while no evidence of exposure was observed in two other facilities.
The World Organisation for Animal Health has recommended monitoring cervids (deer, elk, moose). Exposed deer could serve as a reservoir and a source of new SARS-CoV-2 variants. Moreover, human immune systems may not recognize these new variants.
Serosurveillance in the U.K. deer populations
The U.K. has the highest deer population density in Europe, a relatively high diversity of deer species, and considerable deer-human interactions.
Scientists at the U.K. Health Security Agency (UKHSA) has used deer populations to detect tick-borne encephalitis virus in the U.K. A serosurveillance study in deer looking for SARS-CoV-2 could have three potential outcomes.
- One: no antibody response because the deer are not exposed to SARS-CoV-2.
- Two: positive antibody response due to exposure, but no or low-level transmission.
- Three: positive antibody response post-exposure with transmission and circulation in the deer population.
Deer serum samples were collected in the U.K. between January 2020 and May 2021. Blood samples were collected as soon as possible after culling.
A total of 1,748 serum samples from all U.K. deer species were collected and tested. Sera were tested for the presence of antibodies against the receptor-binding domain (RBD) of the spike protein (S) and the nucleocapsid protein (N). Samples positive for either S or N antibodies were further tested using a surrogate virus neutralization test (sVNT) kit.
No evidence of SARS-CoV-2 exposure in U.K. deer populations
Of the 1,748 serum samples tested, 54 were positive on the S assay and 9 on the N assay. Sixty-three percent of samples positive for S antibodies had very low antibody reactivity. Only 20 samples had measurable antibody reactivity. None of the samples tested showed positivity on both the S and N assays. None of the samples tested positive with the sVNT.
Thus, there was no evidence of SARS-CoV-2 exposure and subsequent seroconversion. Within the 20 positive S assay samples, 5.1% of samples were from roe deer and 3.9% from red deer.
Deer serum samples were collected from across England and Scotland. One sample each was collected from two Welsh counties and none from Northern Ireland. Relatively high S antigen reactivities were observed in Falkirk (25.0%), Aberdeenshire (14.8%), Perth and Kinross (8.1%), and Cumbria (6.4%). The N antigen reactivities were between 0 and 0.7% for all deer species.
Implications of the study
This study shows that SARS-CoV-2 exposure in the wild deer species is different in Northern America and the U.K. The deer species in Northern America and the U.K. are also different. Even so, the U.K. deer species may be susceptible and permissive to SARS-CoV-2 infection.
It is plausible that the transmission routes in Europe and Northern America are different due to differences in human infrastructure and population densities or ecological and behavioral differences between the U.K. deer species and the Northern American white-tailed deer. Experimental exposures of different European deer species to SAR-CoV-2 or comparable in vitro studies would confirm their susceptibility to SARS-CoV-2.
This study included a statistically relevant sample size of the most common deer species, roe, red fallow, and muntjac. Therefore, if there was a prevalence of SARS-CoV-2 in the U.K. deer population, then it would have been observed in this study. Any undetected exposure may be at a very low level or introduced after the study period. The low levels of seropositivity detected by the S and N assays from red and roe deer samples may be due to cross-reactivity with related coronaviruses.
- Holding M, Otter AD, Dowall S, et al. (2022). Screening of wild deer populations for exposure to SARS-CoV-2 in the United Kingdom, 2020-2021. Transboundary and Emerging Diseases. https://doi.org/10.1111/tbed.14534