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White-tailed deer, a species found in all U.S. states except Alaska, appear to contract the coronavirus in the wild, according to the first study to look for evidence of an outbreak in wild deer.
Researchers from the United States Department of Agriculture (USDA) have analyzed blood samples from more than 600 deer in Michigan, Illinois, New York and Pennsylvania over the past decade, and they have found that 40 percent of 152 wild deer tested from January to March 2021 had antibodies against SARS-CoV-2, the virus that causes COVID-19. Three other deer from January 2020 also had antibodies.
Their presence means that the deer likely encountered the virus and then fought it off. The animals did not appear sick, so they likely had asymptomatic infections, the agency said. About 30 million white-tailed deer live in the United States
“The risk of animals transmitting SARS-CoV-2 to humans is considered low,” USDA said National Geographic in a report. Still, the results may suggest that “a secondary reservoir for SARS-CoV-2 has been established in wildlife in the United States,” says Jüergen Richt, veterinarian and director of the University’s Center on Emerging and Zoonotic Infectious Diseases. of Kansas State which was not involved in USDA work. If the virus circulates among other species, it could continue to evolve, perhaps in a way that makes it more serious or transmissible, thus undermining efforts to slow the pandemic.
Earlier this year, researchers established that deer are susceptible to the virus when infected in the lab and can pass the virus to each other. But scientists have not known until now whether infections occur in nature. The only species whose lab results indicate they had contracted the virus from the wild were mink, although cats, dogs, otters, lions, tigers, snow leopards, gorillas and a cougar all had epidemics in captivity or in zoos. (Learn more about efforts to vaccinate some of these animals.)
The new USDA report has been posted on a preprint website, which means it has yet to be peer reviewed. The Centers for Disease Control and Prevention did not respond to the request for comment.
Human transmission
“At this time, there is no evidence that SARS-CoV-2 has an adverse effect on deer. And for humans, our infinitely bigger problem is spread by other humans, ”says Daniel Bausch, a Swiss expert on zoonotic diseases and director of emerging threats and global health security at the FIND association, which works at the development of screening tests related to poverty. diseases.
The USDA says the risk to white-tailed deer hunters is not high. Although researchers believe the virus may have originally passed from animals to humans in a wet market in China, where wild animals were slaughtered and sold for food, the differences in procedures of food preparation are important.
There is “no evidence that you can get COVID-19 from eating [contaminated] food, including wild game meat, ”the USDA says. The department does not issue new guidelines, instead highlighting existing government recommendations on good hygiene when processing animals, which include proper cooking and storage of meat, as well as cleaning and sanitizing all knives, surfaces and equipment.
The exact way the deer may have been exposed to the virus remains unclear, although researchers suspect they were infected from humans. “There are multiple activities that could bring deer into contact with humans, including deer captive operations, field research, conservation work, wildlife tourism, wildlife rehabilitation, supplemental feeding and hunting. The USDA researchers wrote. Other possibilities include that they contracted it through contaminated sewage or exposure to other infected species like mink.
Researchers are also uncertain whether deer transmit the virus to each other or to other species.
Widen the net
There’s a chance the deer won’t have SARS-CoV-2 at all, Bausch says; another explanation is that USDA testing detected antibodies to other coronaviruses, a phenomenon known as cross-reactivity.
The USDA says it’s unlikely. The researchers used a commercially available SARS-CoV-2 antibody test that was found to be very accurate with other species. The USDA also helped rule out cross-reactivity risks by testing a subset of samples using a second type of antibody test even more specific to SARS-CoV-2. The results of this second test mirrored the previous results, suggesting that the tests did pick up anti-SARS-CoV-2 antibodies, the USDA said. National Geographic in a report.
Pre-pandemic blood samples from deer also bolster the results: if the tests only detected antibodies for other coronaviruses, the antibody levels in deer would likely be similar in samples taken before and during the pandemic. Yet when the researchers tested 239 samples taken before January 2020 from a slightly larger pool that also included New Jersey deer, they only had one positive test – as of 2019. (USDA says. that the only outlier was almost certainly a false positive because it had a very low level of antibodies. Richt says the USDA’s false positive conclusion seems reasonable.)
Bausch says performing both types of tests gives him more confidence in the results. Yet, there is still a possibility that cross-reactivity is an issue. “There are many coronaviruses that circulate in animals and probably many that we have yet to find out,” he says. The most definitive ways to rule out cross-reactivity, he says, would be to isolate a virus in cell culture – perhaps by testing for respiratory secretions from deer – but that would require finding a deer when it has an infection. active to coronavirus.
Exposure to the virus appears to vary widely from location to location, the researchers found. Of the four states, Michigan had the highest percentage of deer carrying SARS-CoV-2 antibodies – 67%. Next come Pennsylvania with 44%, New York with 31% and Illinois with 7% of samples showing antibodies. Deer carrying anti-coronavirus antibodies were also concentrated in specific counties, writes the USDA, “with nearly half of the 32 counties sampled showing no evidence” of exposure to the coronavirus, according to the study.
“These results underscore the need for continued and expanded wildlife surveillance to determine the significance of SARS-CoV-2 in free-range deer,” the USDA said. Now, the researchers wrote, it’s also important to look for the virus in predators and scavengers that can eat deer.
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