More than 80 percent of deer in study tested positive for COVID – could be reservoir for continued spread of virus
More than 80 percent of white-tailed deer sampled in various parts of Iowa between December 2020 and January 2021 tested positive for SARS-CoV-2. The percentage of SARS-CoV-2 positive deer increased over the course of the study, with 33% of all deer testing positive. The results suggest that white-tailed deer may be a reservoir for the continued spread of the virus, and raise concerns that new strains may emerge that pose a threat to wildlife and possibly humans.
“This is the first direct detection of SARS-CoV-2 virus in a free-ranging species, and our findings have important implications for the ecology and long-term persistence of the virus,” said Suresh Kuchipudi, Huck Chair in Emerging Infectious Diseases, clinical professor of veterinary medicine and biomedical sciences, and associate director of the Animal Diagnostic Laboratory at Penn State. “These include spread to other free-ranging or captive animals and potential spread to human hosts. Clearly, this indicates that many urgent measures are needed to monitor the spread of the virus in deer and prevent it from spreading to humans.”
According to Vivek Kapur, Huck Distinguished Chair in Global Health and professor of microbiology and infectious diseases at Penn State University, while there is no evidence that SARS-CoV-2 can be transmitted from deer to humans, he believes hunters and people living in close proximity to deer should take precautions, including “contacting or handling the animals by wearing appropriate personal protective equipment and getting vaccinated against COVID-19,” Kapur said.
Previous USDA research found that 40% of white-tailed deer had antibodies to coronavirus. However, Kuchipudi and colleagues point out that these antibodies indicate only indirect exposure to SARS-CoV-2 or an immunologically related organism and do not prove infection with SARS-CoV-2 or the ability to transmit the virus.
In this new study, published Nov. 1 on the preprint server bioRxiv and to be submitted to a peer-reviewed journal, the team examined nearly 300 samples taken from deer in the state of Iowa during the peak of human COVID-19 infection in 2020. The samples – taken from the deer’s retropharyngeal lymph nodes, located in the head and neck – had been collected by the Iowa Department of Natural Resources as part of its routine statewide chronic wasting disease surveillance program. The team tested the samples for SARS-CoV-2 viral RNA using a real-time reverse transcription polymerase chain reaction (RT-PCR) assay, which allows direct detection of infection with the virus.
“We found that 80% of the deer tested in December were positive for SARS-CoV-2, which is about a 50-fold higher positivity rate than that reported at the peak of human infection at that time,” Kuchipudi said. “The number of SARS-CoV-2-positive deer increased from April to December 2020, with the largest increase coinciding with the peak of the deer hunting season last year.”
The team also sequenced the full genomes of all positive samples from the deer and identified 12 SARS-CoV-2 lineages, with B.1.2 and B.1.311 accounting for about 75% of all samples.
“The viral lineages we identified correspond to the same lineages that were circulating in humans at the time,” Kapur said. “The fact that we found several different SARS-CoV-2 lineages circulating in geographically restricted herds across the state suggests the occurrence of multiple independent spillover events from humans to deer, followed by local transmission from deer to deer. This also raises the possibility of reverse transmission from deer to humans, especially in exurban areas with high deer densities.
Kuchipudi added, “The research underscores the urgent need to conduct surveillance programs to monitor the spread of SARS-CoV-2 in deer and other susceptible wildlife species and to develop methods to mitigate possible retransmission.”