As COVID-19 vaccinations become widely available to more people in the U.S. and new treatments for the virus are on the horizon, research suggests there is a new threat that could prolong the pandemic.
Last week, researchers from The Pennsylvania State University found that the COVID-19 pathogen SARS-CoV-2 spread wildly in a population of white-tailed deer, the most widespread deer population in the country. Outbreaks in deer have the potential to spill back into humans, according their study.
“While we lack incontrovertible evidence for spill back (reverse zoonosis) from deer to humans or other free-living animals, our findings warrant a heightened awareness of the potential risks associated with human contact with free-living or captive deer,” the study said.
Research data showed that SARS-CoV-2 was found in one third of white-tailed deer sampled in Iowa from September 2020 to this January. Deer were likely exposed to SARS-CoV-2 “from multiple human-to-deer spillover events and deer-to-deer transmission,” said scientists.
From April 2020 to December 2020, researchers evaluated 283 retropharyngeal lymph node samples collected from 151 free-living and 132 captive deer in Iowa. Of these, 33.2% were positive for SARS CoV-2 RNA.
“It was actually quite stunning to us,” said veterinary microbiologist Vivek Kapur at Penn State, who aco-led the study, according to NPR. “We were very surprised to see such a high number of positive samples.”
There are an estimated 25 million white-tailed deer in the U.S., said the study. Deer hunting is the most popular type of hunting in the nation – it contributed over $20 billion to the U.S. GDP and supported more than 300,000 jobs in 2016.
In Texas, where the white-tailed deer population is estimated at 5.3 million, deer hunting generates $1.2 billion in economic output.
Veterinarian Dr. Mike Hutchinson told Audacy’s KDKA radio in Pittsburgh this week that hunters shouldn’t be too worried about catching COVID-19 from deer. However, they should be careful and wear gloves while handling the animals.
According to the Penn State study, “most viruses causing disease in humans originated in animals and many are capable of transmitting among multiple species,” and the reservoir host for SARS-CoV-2 is still unknown. Many animal species are susceptible to the virus and could act as reservoirs.
“Our results suggest that deer have the potential to emerge as a major reservoir host for SARS-CoV-2, a finding that has important implications for the virus genomic diversity and future trajectory of the pandemic,” said the study.
In addition to the potential risk that deer infections could spill over into human populations, the researchers explained that viral mutation can occur in a revisor host such as white-tailed deer, increasing the virus’ ability to cause disease.
“Animal reservoirs are also rife with a plethora of other CoVs with which SARS-CoV-2 will be afforded the opportunity to recombine, opening potential avenues for the acquisition of genes that might serve to increase virulence, transmissibility, pathogenicity, and immune evasion,” they said.
Evidence of this has already been found after a mink spillover event in Denmark.
Another potential danger of animal-related COVID-19 outbreaks is how they can preserve strains of a virus.
“Human viruses under immune pressure may diverge, whereas those circulating in wild reservoirs may not,” said the researchers. “Reintroduction of these viruses into a future human could lead to outbreaks in young human humans who were never exposed to the ancestral pandemic strains.”
According to the study, this is the most likely scenario behind the 2009 A-H1N1 swine flu pandemic, which was related to the 1918 pandemic strain as well as others from the 20th century.
Findings from the study indicate “an urgent need for expanded active surveillance of potential wildlife reservoirs,” researchers said.
Researchers acknowledged that there were limitations to their study. Findings came from just one state and samplings were not uniform throughout the state. Samples were also from early on in the pandemic, before the Delta variant was in high transmission.
Previous studies have also shown how white-tailed deer and other animals are vulnerable to SARS- CoV-2.
“We also have detected the virus in deer in Ohio,” said virologist Linda Saif at The Ohio State University's College of Veterinary Medicine, according to NPR. “And there are antibody studies that suggest the prevalence of COVID infections among deer are pretty high in the Midwest and East.”
Veterinary virologist Suresh Kuchipudi at Penn State, who co-led the study with Kapur, said monitoring the virus in wildlife is an important way to be proactive about emerging variants going forward, “especially in animals that could serve as a reservoir, like the deer.”
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