It looks like the new coronavirus has somehow passed from humans to wild deer in parts of the United States.
In the northeast of the country, in a recent federal study, neutralizing antibodies to SARS-CoV-2 were found in 40% of all white-tailed deer (Odocoileus virginianus) sampled.
In Michigan alone, 67 percent of free-living deer have been found to have immune markers for coronavirus in their blood.
This is the first evidence of widespread exposure to SARS-CoV-2 in wildlife, and the results of this study are troubling.
Although none of the deer showed negative health effects, the presence of specific antibodies in their blood suggests that they recently fought the virus.
Scientists fear that by secretly conserving and spreading this pathogen, deer populations are allowing SARS-CoV-2 to adapt and evolve into new strains - those that can re-infect humans years later with even greater transmission and severity than before.
After all, white-tailed deer in the United States often overlap with our species, whether in field work, conservation, feeding, hunting, or in sewage, providing an ideal pathway for the virus to spread back and forth.
"The geographic distribution of this species covers most of North America, and these animals are especially abundant near urban settlements located in the eastern United States," the authors write in their work.
"Moreover, white-tailed deer can form social groups - a contact structure capable of supporting the intraspecific transmission of many pathogens."
Ever since the global pandemic began, scientists have worried that the new coronavirus could pass from humans to another animal species, known as a zoonotic diversion.
Last year, for example, an outbreak in farmed minks led to massive culling in Europe and the United States. But unlike captive animals, infections in wild animals are not easy to control.
This is why scientists are so concerned about the latest research findings. If SARS-CoV-2 can indeed find refuge in the wild, it could make it extremely difficult to eradicate. If the virus adapts among other species and then re-infects humans, our vaccines may be much less effective in the future.
Recently in Utah, a seemingly healthy wild mink tested positive for SARS-CoV-2, becoming the first free-living animal to contract the virus. However, as scientists predicted, this was probably just the tip of the iceberg. Now the virus appears to have spread to wild deer as well.
If we want to be absolutely sure that these free-walking animals are a reservoir for the new coronavirus, they need to be tested for viral RNA, but the presence of antibodies in their blood suggests that they have somehow become infected.
Previous laboratory studies have shown that white-tailed deer are highly susceptible to SARS-CoV-2, and that one infected individual of this species can infect another.
A new study suggests that this spread may also occur in the wild, although more research is needed to figure out how this happens.
The team gained access to 385 wild white-tailed deer serum samples from January to March 2021, as well as 239 archived samples from 2011 to 2020, which they tested for antibodies to SARS-CoV-2.
Prior to the outbreak of the pandemic in 2019, government researchers had not found any immune markers for the SARS-CoV-2 virus in the blood of wild deer. However, after the outbreak of the pandemic, these antibodies began to appear more and more often.
In 2020, SARS-CoV-2 specific blood proteins were found in three deer. However, during the first three months of this year, nearly half of all 385 blood samples taken from deer in Michigan, Pennsylvania, Illinois and New York showed the same neutralizing antibodies.
How exactly these deer got infected with the virus is not yet clear. It could pass directly from humans, or it could be transmitted from livestock or wild animals in contact with us, and then get on white-tailed deer.
In this regard, US officials are calling for increased surveillance of wildlife, especially predators and scavengers that regularly interact with deer.
"If there is a common source of infection in deer, it is likely that the same source could infect other animals," said virologist Arinjay Banerjee of the University of Saskatchewan, who was not involved in the study, in an interview with Nature.
Perhaps SARS-CoV-2 is entering the wild faster than we can catch it."
The study was published in the journal bioRxiv.