More than half of Michigan’s deer appear to have been exposed to SARS-CoV-2

The U.S. Department of Agriculture released some rather disturbing news on Wednesday: A survey of wild deer populations found that large numbers of animals appear to have been exposed to SARS-CoV-2, the virus that causes the COVID-19. The discovery indicates that there is a very large population of wild animals in North America that could serve as a reservoir for the virus, even if we were to control its circulation within the human population.

Probably not a mistake

Why check the deer in the first place? It turns out that the USDA’s Animal and Plant Health Inspection Service is studying a variety of species “to identify species that may serve as reservoirs or hosts for the virus, as well as to understand the virus. origin of the virus and predict its impacts on flora and fauna. the risks of interspecies transmission. ”This is the same group that identified the spread of the virus to a wild mink in 2020.

Using a captive deer population, the USDA had previously determined that deer could be infected with the virus, although the animals showed no symptoms. So, although direct interactions between deer and humans are relatively limited, verifying wild populations made sense. The USDA tested populations in a total of 32 counties in four different states, obtaining blood samples to look for antibodies specific to SARS-CoV-2.

Antibodies were fairly common, ranging from a low of 7 percent of samples in Illinois to a high of 60 percent in Michigan. In total, a third of the deer tested had antibodies against SARS-CoV-2.

The USDA also took reasonable precautions to ensure the data was accurate. Agency scientists tested samples that existed before the pandemic to confirm that the false positive rate was (it was) low. The researchers also performed antibody tests using two different machines to make sure the finding wasn’t due to some sort of hardware problem (it wasn’t). So, in all likelihood, a large number of deer have been exposed to the virus.

What does that mean?

Right now, we’ve spent a lot of time studying how SARS-CoV-2 spreads, and prolonged exposure to respiratory droplets is the most effective method. There are not many contexts in which this type of exposure is likely to occur between humans and wild deer. It is possible that these numbers are generated by rare transmission to deer followed by wide spread within the population. Or another species, possibly domesticated, carries the virus between humans and deer.

Understanding how transmission takes place will be essential in determining whether the existence of a large viral reservoir in deer poses a threat to humans. Although there has been no indication that a human has acquired an infection from a deer, the virus is so common in the American population that it would be difficult to rule out human-to-human transmission as an alternative explanation for all cases. . Yet if the United States ever manages to control the spread of the virus, it would be wise to know about all the alternative routes of infection.

Another problem is that the virus can pick up mutations that help it adapt to deer as a host and prove to be dangerous to humans if the virus returns to humans. So far, the only time this has been studied with SARS-CoV-2 is a strain that adapts to mink. This virus becomes less efficient at infecting human cells, but it also evolves in a way that makes it less sensitive to the immune response generated by vaccines or previous infections. There is, of course, no reason to believe that a deer-friendly SARS-CoV-2 would follow a similar trajectory.

Either way, both of these issues – the presence of a reservoir that is difficult to control and the prospect of the virus developing further – mean that it will be important to understand how the virus reaches the deer population and whether it spreads. spread among deer.