A third of the white-tailed deer tested in four states during a federal study had been exposed to the coronavirus, in yet another indication of the unpredictable nature of the disease. The percentage was highest in Michigan, where 60 percent of the animals tested positive.
The presence of the virus in wild deer is not just a curiosity for scientists. The virus has shown it can jump from one species to another, and in the worse case, it could become established in a common animal species, creating a reservoir from which the virus could spill back into humans.
“It’s not just a warning about deer,” said Tony Goldberg, a veterinarian at the University of Wisconsin, Madison, who has been surveying North American bats for evidence of infections with the coronavirus.
The deer could have encountered the virus through contact or proximity to other animals or humans. Exposure is not the same as infection; the blood tests detected antibodies, which could indicate that the deer fought off infection.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service conducted the survey because deer have been shown to be susceptible to infection and are often in contact with people. Researchers tested blood samples from deer in Illinois, Michigan, New York and Pennsylvania in 2020 and 2021. The findings have not yet been published in a scientific journal.
Researchers have experimentally infected ferrets, primates and other animals with the coronavirus in the laboratory, and dogs, domestic cats, gorillas and other animals in zoos.
Farmed mink caught the virus naturally from humans. The virus mutated and spread back to humans in a few cases. Farmed mink are now being vaccinated with an experimental vaccine, as are zoo animals.
North American bat species, Dr. Goldberg said, showed no evidence of infection so far. They are significantly different from the Asian bat species that are suspected to be the original hosts of the virus.
Dr. Goldberg said it was difficult to know what close contact with people meant for deer. The animals are often in yards and gardens, but, he joked, not often invited to dinner parties. People could conceivably sneeze on a leaf or into the air with deer nearby, he said, scenarios that seemed “plausible but not likely.”
He added that if one deer became infected, however, it might well infect or expose other deer to the virus. Sewage also can contain the coronavirus.
The survey clearly set off an alarm worth paying attention to. “Please add this finding as reason no. 2,784 to get vaccinated,” Dr. Goldberg said.