The doe came into the staging area near Morgan, Utah, like any other deer during the December mule deer health assessments–slung underneath the belly of a Hughes 500 helicopter. She was given the identification number MG1129 at the time, not knowing how famous she'd become as the first mule deer to test positive for SARS-CoV-2, the virus that causes COVID-19.

As part of these winter 2021 health assessments, researchers recorded information on fat reserves, general health, and collected blood samples and nasal swabs before attaching a GPS-equipped radio collar. The blood samples serve several purposes, but along with the nasal swabs, contribute to a national effort to monitor wildlife diseases. In this case, Congress provided the U. S. Department of Agriculture (USDA) with $300 million through the 2021 American Rescue Plan to look specifically for SARS-CoV-2 in wildlife species. Deer are a species of interest because they share the same primary SARS-CoV-2 host cell receptor (hACE2) with humans, which means they are susceptible to infection from this virus. The USDA surveillance effort is producing a growing body of information to help us understand if deer play a role in the spread of this virus.

Although this is the first time the virus has been detected in mule deer, whitetails in the East are showing a surprisingly high rate of exposure to the SARS-CoV-2. For example, 40% of 385 whitetail samples collected from January through March 2021 in Illinois, Pennsylvania, Michigan, and New York contained antibodies showing they were exposed to SARS-CoV-2.

To make sure they weren’t mistakenly detecting some other common coronavirus, researchers pulled deer serum samples from prior to 2020 out of the freezer from those areas and tested them. Results showed that deer were not exposed to SARS-CoV-2 until the worldwide pandemic swept through the human population. Other testing in the East showed many whitetails were exposed to the virus in Iowa (33%), Ohio (36%), Staten Island, New York (15%), Quebec (5.6%), Ontario (6%), and Texas (0-94% among captive facilities). Interestingly, researchers in several of these studies were able to show that the viral strains circulating in the human population at the time were the same ones the deer were carrying. It is clear that deer are being exposed to the virus from humans and then spreading it amongst themselves.

So, are humans giving deer COVID-19? Not exactly. Deer are being exposed to the virus that causes it, but no deer have been documented with any clinical signs of being sick with COVID-19. Deer do a pretty good job of social distancing from humans, so it's not clear how deer might be getting infected with this virus. However, all evidence points to contact with humans or human waste. Humans and whitetails interact much more in the Eastern U.S. because deer have adapted to our presence and wander through backyards to eat our shrubs and gardens. With lower-density human and deer populations in the West, we had reason to believe the exposure of deer to SARS-CoV-2 would be less frequent—but not absent.

The now-famous MG1129 contributed a deep nasal swab along with 249 other deer captured last winter. All these swabs were sent to the USDA National Wildlife Research Center in Fort Collins, Colorado, but MG1129 was the only one positive for SARS-CoV-2. Her sample was then sent to their National Veterinary Services Laboratories in Ames, Iowa, for a second opinion and they confirmed it as a Delta variant on March 22. Nasal swabs identify animals that are actively shedding the virus because of recent exposure, but looking for antibodies in the blood allows wildlife health professionals to detect past exposure to the virus. Researchers also collected blood samples from almost all of those same deer and are currently validating the test results. However, preliminary findings indicate at least 5% of the deer sampled may have been exposed to the virus at some point.

What keeps disease experts up at night is the worry that SARS-CoV-2 will circulate independently in the deer population, separate from humans, and mutate slowly as it is passed from deer to deer. If that happens, the virus could mutate in ways that would make it more dangerous if then passed back to us. If a virus circulates and changes separately from humans, that means no humans are adapting to these viral changes along the way. As it turns out, there are a couple of cases that do not help disease experts get back to sleep.

Mink are susceptible to SARS-CoV-2 infection. Surveillance in the Netherlands documented the virus circulating in 16 mink farms and mutating as it did into a slightly different version. Intensive testing at the time detected the mutated mink version of the virus in 68% of the mink farmworkers, most of whom developed symptoms of COVID-19. Luckily, there was nothing unusual about their symptoms.

More recently, research identified a very different version of the Omicron variant circulating among 6% of the whitetails sampled in southwestern Ontario, Canada. Genetic evidence indicates it was circulating in deer separate from humans for quite a while. This altered version of Omicron was then detected in a person who worked closely with deer. This was the only human case identified and it was apparently not any more dangerous than other variants.

Despite the widespread occurrence of this virus in deer and the potentially problematic scenarios one can dream up, experts are not concerned about deer perpetuating the COVID-19 pandemic. Dr. Ginger Stout, a wildlife veterinarian for the Utah Division of Wildlife Resources (UDWR), said: “There is no evidence that deer are playing a significant role in spreading SARS-CoV-2 to people, and the available research suggests that the likelihood of getting COVID-19 from an animal is quite low.”

Kent Hersey of UDWR and Brock McMillan from Brigham Young University both handled MG1129 during the capture operations last December; handled in a very literal sense, which means they had their hands in her mouth while they peered into the darkness to see and feel the wear pattern of her teeth to determine her age. Eight to 10 people helped restrain and process her, but there were no reports of anyone with flu-like symptoms afterward. The only thing they took away from that interaction was the knowledge that she was around 2.5 years old.

Hersey, McMillan, and a huge army of collaborators and volunteers have captured 577 mule deer and have physically handled 1,100 ungulates this year in Utah. Like MG1129, none of these animals showed symptoms of COVID-19. Deer only shed the virus in the environment for only three to five days after being infected, so the fact that some percentage of the population has antibodies from an exposure sometime in the past doesn't mean we should quarantine ourselves during deer season.

How these deer were exposed to the virus in the first place remains a mystery. MG1129 was captured a few miles from the nearest town and her GPS collar shows she is doing fine. Her locations give no indication she visits town. With 1,215 mule deer currently GPS-collared in Utah, they have a pretty good handle on factors affecting deer populations in the state. Hersey said, “We have had no mortalities that caused us to suspect COVID-19, and there is no evidence it is affecting any deer population in the state.”

There is also no evidence that people can get COVID-19 by preparing or eating meat from an animal infected with SARS-CoV-2. According to the Center for Disease Control and Prevention (CDC), to completely inactivate this virus it only takes 3 minutes at 160° F, 5 minutes above 149° F, and 20 minutes above 140° F.

The best source of reliable information on this topic is always acronyms like USDA and CDC, not other combinations of the alphabet associated with news outlets. As the USDA continues its surveillance and study of the relationship between deer and SARS-CoV-2 circulation, we will be learning a lot more in the near future. For now, there is no cause for alarm and no need to do anything differently.

Feature image via Randy Larsen.

Jim Heffelfinger

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COVID-19 Virus Discovered in Mule Deer for First Time