Photo courtesy of the Illinois Department of Natural Resources.

November 1, 2023

SARS-CoV-2 in Illinois White-tailed Deer

U.S. wildlife agencies continue to learn about the effects of SARS-CoV-2 (SCV2), the virus that causes COVID-19, on wild white-tailed deer populations in Illinois. U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) seeks answers to questions, such as,

  • Is this virus persistent and circulating throughout our deer populations?
  • Are there any State or regional differences between infection rates, genetic lineages, or habitat types?
  • What are the likely transmission routes that led to this exposure in wild white-tailed deer?

APHIS’s Wildlife Services has these questions in its sight and hopes to formulate answers with cooperation from the deer hunters within the state regions.

In January 2021, APHIS Wildlife Services detected evidence of prior infection of wild white-tailed deer populations as part of a four-state pilot program, including Illinois, Michigan, Pennsylvania and New York. APHIS Wildlife Services leveraged deer hunters to assist with this project, since more than 6 million animals are harvested annually nationwide, with nearly 77,000 deer harvested in Illinois during the hunting seasons annually. During this initiative, hunters and biologists collected 385 samples, and screening of the samples revealed SCV2 antibodies in 40 percent of white-tailed deer.

A chart explaining 2022 research done on Illinois white-tailed Deer. Text on the chart includes: County prevalence rates ranged from 0% to 16.4%, averaging 6.4% across all sampled Illinois counties. This was well below the national prevalence rate of 12.3%. To investigate prior exposure to SCV2 in Illinois' wild deer population, 1,015 blood samples were also collected and tested, resulting in a 25.4% detection.

Sampling wild animal populations can be a challenging and costly endeavor. Beginning in November of 2021, with funding and support from the American Rescue Plan Act, APHIS Wildlife Services partnered with the Illinois Department of Natural Resources to leverage hunter-harvested samples from mandatory Chronic Wasting Disease check stations from the northern part of the state during the 2022 deer harvest season. Through this partnership and voluntary sampling opportunities offered to hunters, APHIS Wildlife Services collected and tested 987 samples from wild white-tailed deer across 21 counties, making Illinois one of the top contributors to this study out of 28 other participating states. These samples were submitted to APHIS National Wildlife Research Center for further diagnostics. Samples collected by biologists included:

  • Nasal swabs (testing for active infection and shedding of the SCV2 virus).
  • Blood samples on small filter paper cards looking for antibodies (suggesting a previous infection to SCV2).
A biologist collects a specimen sample by using a nasal swab on a harvest gray adult male deer.
Nasal swabs were collected from deer checked in at mandatory Chronic Wasting Disease check stations to test for the SCV2 virus. Photo courtesy of the author.

Within Illinois, we detected evidence of active infection in 63 out of 987 swab samples within 13 of the 21 counties sampled.

Infected deer, wild or captive, do not appear to exhibit clinical signs of COVID-19. Knowing this information, why should hunters and wildlife managers be concerned about this virus? Considering the pilot surveillance program results, researchers agree that more studies are needed to understand the geographic scope of infection in white-tailed deer populations and any potential impacts to humans. Further surveillance will provide wildlife managers with a better understanding of transmission pathways, whether wild white-tailed deer are serving as a reservoir species, and which variants are circulating or could potentially emerge.

The critical point is that while deer can be infected with SCV2, there is little evidence that this virus can be transmitted to humans during field dressing or preparing venison. As always, hunters are encouraged to wear protective gloves and use proper hygienic practices when handling and preparing meat, as recommended by the Centers for Disease Control and Prevention. These practices include:

  • Not harvesting animals that appear sick or are found dead.
  • Washing your hands and equipment thoroughly after cleaning game.
  • Cooking meat to an internal temperature of 165° F or higher.

While some questions remain unanswered, this important work assisted in creating a baseline for future surveillance, as well as opportunities for future research. Examples of future research could include investigating the source of virus introduction and transmission pathways, if the virus has any adverse effects on wildlife or human health, and monitoring any possible mutations that may be occurring in wild white-tailed deer populations.

A wooden board with a line of binder clips along the bottom of the board. Above each clip is a letter of the alphabet. Each binder clip holds a piece of paper. Some of the papers have been dipped in blood samples of white-tailed deer.
Nobuto strips are specialty strips have been used to track the health of the Illinois deer population. Photo courtesy of the author.

Year 2 of this national study wrapped up at the end of the 2022-23 hunting season, which expanded to include elk, moose and mule deer. Year 3 will begin during the 2023-24 deer hunting season and hunters will have the opportunity to have their harvested deer included as part of this study when they stop at a Chronic Wasting Disease check station.

APHIS is currently conducting multiple projects related to SCV2 aimed at understanding how virus behaves in different animals, how it moves between animals and people and what we and our public health partners can do to interrupt the chain of transmission. APHIS’ American Rescue Plan strategic framework outlines how the agency is focusing its efforts to prevent, detect, investigate and respond to SCV2 in animals, as well as other emerging diseases that could pose a threat to humans and animals.

APHIS and its One Health partners work together to harness the unique skills, knowledge, specific perspectives, and experiences to strengthen its understanding of SCV2 and enhance its ability to detect diseases sooner. We believe this highlights the importance of this ongoing work along with our other efforts to study this virus across a variety of animals, such as wildlife, domestic and zoo animals.

Mitch Oswald is a Wildlife Disease Biologist for the United States Department of Agriculture’s branch of Wildlife Services. Oswald is a 2014 graduate of Blackburn College in Environmental Biology. He currently works in the State Office in Springfield and has overseen disease surveillance projects for the agency since 2019. He is an avid outdoorsman and enjoys hunting, fishing and anything that gets him outdoors. He currently resides in Carlinville.

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