Buck Trends: USU Researcher Tracking COVID-19 Virus in Utah's Mule Deer Populations

Humans don’t hold a monopoly on COVID-19 infections — we’ve passed the virus on to other animals: dogs, cats, lions, mink and deer, to name a few, and researchers don’t yet know much about how SARS-CoV-2 (the virus that causes COVID-19) moves through animal populations. Kezia Manlove from the Quinney College of Natural Resources is working to change that.

Manlove is leading a team at Utah State University as part of a cooperative project with the U.S. Department of Agriculture Animal and Plant Health Inspection Service (USDA APHIS), the U.S. Geological Survey, and seven other academic institutions to uncover more about how SARS-CoV-2 persists and spreads in deer populations.

Research early in the SARS-CoV-2 pandemic confirmed that deer could be infected with the virus, sometimes in large numbers. People often share space with deer, both during hunts and in suburban yards. According to Manlove, a disease ecologist from the Department of Wildland Resources, it’s vital to know how the virus might act in these situations and how long it lasts. Understanding which deer get infected and for how long is important, she said, since those factors help determine whether deer have the potential to be reservoirs for future human infections.

“Basically, we're trying to answer the question: Could deer become a relevant source of new SARS-CoV-2 strains that could periodically spill back into the human population? And if so, in what context and how often might we expect those spillback events to happen?” Manlove said.

The team was recently awarded $1.1 million in a cooperative agreement with USDA APHIS through American Rescue Plan Act funds to conduct collaborative, targeted surveillance of SARS-CoV-2 in mule deer. She partnered with the Utah Division of Wildlife Resources to test deer for the virus, and to track how the animals move across the landscape, potentially carrying SARS-CoV-2 with them. Data from the project could be a foundation for understanding more about the possibility of the virus mutating and spreading back to humans — a phenomenon called spillback, she said.

The team will capture, release, and track 480 deer over two years at 12 sites in seven states across the country. Each deer will be tested twice a year for active SARS-CoV-2 infection and for the antibodies that signal previous infections. Three of the sites in Utah — the La Sal Mountains, San Juan County, and Mount Nebo — will be coordinated by the USU team. The researchers will track the animals using GPS collars that send signals every 30-minutes, offering detailed information about the movements and interactions that could lead to virus transmission.

Deer have been tested for SARS-CoV-2 across the country through hunter harvest, and through live-animal testing as part of standard Utah Division of Wildlife Resources captures in the state last year. But hunters don't select their deer at random; they tend to target older, male animals. The combination of Wildlife Resources and hunter-harvest data showed low rates of SARS-CoV-2 in mule deer, but rates as high as 30 percent in white-tailed deer.

Researchers have speculated that mule deer may have lower rates of infection because of their distinct migratory patterns and lower herd densities, or perhaps because they have lower susceptibility, viral shedding or pathogen transmission rates. It could also be that the deer that were tested weren’t representative of the population as a whole.

“That’s one hypothesis we’re hoping to test as the project progresses,” Manlove said.

“Hunter harvest and live-animal surveillance samples from captures remain a really important source of data, but they can be hard to interpret," Manlove said. “Another goal of the project is to provide higher-quality data from a set of diverse sites across the country that we can use to calibrate the more opportunistic information that the USDA APHIS and its state partners gather."

As of now, it’s not clear what role mule deer could ultimately play in SARS-CoV-2 dynamics. The research may actually find that mule deer are very competent hosts, Manlove said. It’s a big unknown, which underscores the importance of this pioneering project, especially for a species that often makes its way into human-occupied environments.