White-tailed deer (Odocoileus virginianus) are abundant in the United States; they can be seen bounding around rural and urban areas in every state except for Alaska. A new survey carried out by the U.S. Department of Agriculture (USDA) detected antibodies for SARS-CoV-2 in wild deer populations in four states. Meaning that the deer contracted coronavirus in the wild and fought off the infection, reports Dina Fine Maron for National Geographic.
The results are the first to look at widespread exposures of SARS-CoV-2 in wild animals and were published on the preprint server bioRxiv in July. The findings have not yet been officially peer-reviewed.
Previous studies have shown that white-tailed deer are susceptible to SARS-CoV-2 infections and can spread the virus to other deer in laboratory settings, reports Nature's Smriti Mallapaty. Until now, it was unknown if infections between deer in the wild were occurring. Mink are the only animals to have contracted the virus in the wild, National Geographic reports. However, cats, dogs, otters, lions, snow leopard, gorillas and tigers have all tested positive for the virus in captivity.
To see if infections were occurring in deer, scientists obtained both pre-pandemic and post-pandemic blood samples from 624 deer located in Michigan, Illinois, Pennsylvania, and New York, per National Geographic. After analyzing 385 blood samples collected between January and March 2021, 40 percent, or 152 wild deer, had antibodies for SARS-CoV-2, Nature reports. Michigan saw the highest percentage of deer primed with antibodies for the virus at 67 percent out of 113 samples, reports James Gorman for the New York Times. Three wild deer blood samples from January 2020, when the virus was just beginning to spread in the U.S., also contained antibodies, Nature reports.
"Given the percentage of samples in this study that had detectable antibodies, as well as the high numbers of white-tailed deer throughout the United States and their close contact with people, it is likely that deer in other states have also been exposed to the virus," a USDA spokesperson told Nature.
The antibodies in the serum samples suggest that the deer contracted coronavirus, and their immune systems fought the infection. However, while researchers detected antibodies in the deer's blood samples, the mammals showed no symptoms of illness. How the deer contracted SARs-CoV-2 is still unknown. Per National Geographic, the animals could have contracted the virus from humans, other animals in the wild, or through contaminated wastewater.
Researchers are concerned with infections occurring in the wild because of the virus's ability to mutate and jump from one species to another, which could create a reservoir for the virus to mutate and infect humans, the New York Times reports.
Reservoirs occur when the virus stays within a small group of infected animals. Once established, it can mutate and possibly evolve resistance toward vaccines and emerge as a different strain even after the pandemic ends, Nature reports. To see if the deer are a reservoir for coronavirus, the team would have to test the animals for viral RNA. This study only focused on testing for antibodies, per Nature.
The USDA also notes that only a few deer populations in four states were tested and do not represent the entire deer population across the country. The USDA explains in a statement that more research is needed to find how wild deer were exposed. Additional investigations will need to be done to evaluate the potential impacts the virus may have on deer populations overall, other wildlife, and people that come into contact with infected deer.
"These results emphasize the need for continued and expanded wildlife surveillance to determine the significance of SARS-CoV-2 in free-ranging deer," a USDA spokesperson tells National Geographic.