The doe entered the staging area near Morgan, Utah, like any other deer during the December mule deer health assessments, perched under the belly of a Hughes 500 helicopter. It was given ID number MG1129 at the time, unaware of how famous she had 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 stores, general health, and collected blood samples and nasal swabs before donning a GPS-equipped radio collar. The blood samples serve several purposes, but together with the nasal swabs, they contribute to a national effort to monitor wildlife diseases. In this case, Congress provided the US Department of Agriculture (USDA) $300 million through the 2021 American Rescue Plan to specifically search for SARS-CoV-2 in wildlife species. Deer are a species of interest because they share the same primary host cell receptor for SARS-CoV-2 (hACE2) with humans, meaning they are susceptible to infection by 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, white-tailed deer in the east show a surprisingly high rate of exposure to SARS-CoV-2. For example, 40% of 385 whitetail samples collected between January and March 2021 in Illinois, Pennsylvania, Michigan, and New York contained antibodies showing they had been exposed to SARS-CoV-2.
To make sure they weren’t mistakenly detecting some other common coronavirus, the researchers took pre-2020 deer serum samples from the freezer in those areas and tested them. The results showed that deer were not exposed to SARS-CoV-2 until the global pandemic wiped out the human population. Other tests in the east showed that 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 installations). 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 carried by deer. It is clear that deer are exposed to the virus from humans and then spread it among themselves.
So are humans giving deer COVID-19? Not quite. Deer are exposed to the virus that causes it, but no deer with clinical signs of being ill with COVID-19 have been documented. Deer do a good job of social distancing from humans, so it’s not clear how deer could become infected with this virus. However, all evidence points to contact with humans or human waste. Humans and whitetails interact much more in the eastern US because deer have adapted to our presence and roam our backyards eating our bushes and gardens. With denser human and deer populations in the West, we had reason to believe that deer exposure to SARS-CoV-2 would be less frequent, but not non-existent.
The now famous MG1129 contributed a deep nasal swab along with 249 other deer captured last winter. All of 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. His 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 due to recent exposure, but looking for antibodies in the blood allows wildlife health professionals to detect past exposures to the virus. The researchers also collected blood samples from nearly all of those same deer and are currently validating the test results. However, preliminary findings indicate that at least 5% of sampled deer may have been exposed to the virus at some point.
Keeping disease experts awake is concern that SARS-CoV-2 circulates independently in the deer population, spreading from humans and slowly mutating as it passes from deer to deer. If that happens, the virus could mutate in ways that would make it more dangerous if it were to spread to us later. If a virus circulates and changes separately from humans, that means no humans are adapting to these viral changes along the way. Turns out there are a couple of cases that don’t help disease experts get back to sleep.
Mink are susceptible to SARS-CoV-2 infection. Surveillance in the Netherlands documented that the virus was circulating in 16 mink farms and mutating into a slightly different version. Intensive testing at the time detected the mutated mink version of the virus in 68% of mink farm workers, most of whom developed symptoms of COVID-19. Fortunately, there was nothing unusual about her symptoms.
More recently, research identified a very different version of the Omicron variant circulating among 6% of whitetails sampled in southwestern Ontario, Canada. Genetic evidence indicates that it was circulating in deer separate from humans for quite some time. This altered version of Omicron was later detected in a person who worked closely with deer. This was the only human case identified and was apparently no more dangerous than other variants.
Despite the widespread occurrence of this virus in deer and the potentially problematic scenarios one can imagine, experts are not concerned that deer will perpetuate the COVID-19 pandemic. Dr. Ginger Stout, a wildlife veterinarian with 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 wildlife. people, and the available research suggests that the chance of contracting COVID-19 from an animal is quite low.”
UDWR’s Kent Hersey and Brigham Young University’s Brock McMillan handled MG1129 during capture operations last December; manipulated in a very literal sense, meaning they had their hands in their mouths as they peered into the dark to see and feel the wear pattern on their teeth to determine their age. Eight to 10 people helped restrain and process her, but there were no reports of anyone having flu-like symptoms afterward. The only thing they got out of that interaction was the knowledge that she was about 2.5 years old.
Hersey, McMillan and a huge army of collaborators and volunteers captured 577 mule deer and 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 just three to five days after becoming infected, so just because a percentage of the population has antibodies from a past exposure doesn’t mean we should quarantine for the season of deer
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 that she is doing well. Their locations give no indication that they visit the city. With 1,215 mule deer currently GPS-collared in Utah, they have a good handle on the factors affecting deer populations in the state. Hersey said, “We have had no deaths that would cause us to suspect COVID-19, and there is no evidence that 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 Centers for Disease Control and Prevention (CDC), it takes only 3 minutes at 160°F, 5 minutes above 149°F, and 20 minutes above 140°F to completely inactivate this virus.
The best source of reliable information on this topic is always acronyms like USDA and CDC, not other combinations of the alphabet associated with the media. As the USDA continues its surveillance and study of the relationship between deer and SARS-CoV-2 circulation, we will learn much more in the near future. For now, there is no cause for alarm and no need to do anything different.
Featured image via Randy Larsen.