Several studies of free-ranging, white-tail deer in the upper mid-west and on the east coast have found that roughly a third of all animals tested have been infected by the COVID-19 virus.
Last August investigators with the US Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) announced that serum samples taken from white-tail deer populations in Illinois, Michigan, New York, and Pennsylvania all contained anti-bodies showing they’ d been exposed to SARS-CoV-2, the virus that causes COVID-19. The virus was most common in white-tail deer populations in Michigan, where 67% of all test samples detected COVID-19 antibodies.
A similar study by researchers at Pennsylvania State University yielded comparable results, where 94 of the 283 white-tailed deer tested positive for COVID-19 antibodies. The Penn State study focused upon both free-ranging and captive white-tail deer in Iowa, and was conducted between September 2020 and January 2021.
Thus far there have been no reports of wild deer being sickened by COVID-19, and none of the captive deer experimentally infected with SARS-CoV-2 have expressed clinical signs of the illness. However, researchers are concerned that widespread infections of COVID-19 within white-tail deer populations could create a reservoir of the virus, independent of human populations, that could potentially mutate within the animal and then reinfect humans with a new variant.
“The deer apparently live with COVID-19 quite well, but rapidly spread it amongst the herds,” said Dr. Kevin Kavanagh in an interview with the medical journal Infection Control Today. “That’s actually very problematic, because if it finds a host that it doesn’t make sick … it can mutate and change and then reinfect other animals plus mankind. That is one of the worrisome scenarios that could take place.”
The Centers for Disease Control and Prevention (CDC) reports that some coronaviruses that infect animals can be spread to people, and then spread between people, but the incidence in rare.
“This is what happened with SARS-CoV-2, which likely originated in bats,” the CDC reports. “At this time, there is no evidence that animals play a significant role in spreading SARS-CoV-2, the virus that causes COVID-19, to people. Based on the available information to date, the risk of animals spreading COVID-19 to people is considered to be low.”
Still, the widespread occurrence of COVID-19 in deer is concerning, in large part because white-tail populations exist in every state of the United States except Alaska, and often come in close contact with humans. The US Fish and Wildlife Service estimates the total nationwide population of white-tail deer to be around 30 million animals.
According to the CDC the transmission of infectious disease from animals to humans is very common, both in the United States and around the world. The CDC estimates that more than six out of every 10 known infectious diseases in people can be spread from animals, and three of every four new or emerging infectious diseases in people come from animals. Common examples of these “zoonotic” diseases include salmonella, West Nile virus and Lyme disease.
However, the reverse process is far less common. Animals do not typically contract infectious disease through human contact.
APHIS researchers emphasize that exactly how the deer were exposed to COVID-19 remains unknown, but the fact that no SARS-CoV-2 antibodies have been detected in samples taken from deer prior to January 2020 suggests the virus spread from humans to deer and not the other way around.
“While the precise route(s) of transmission of SARS-Cov-2 from humans to deer are unknown, there are several ways in which deer may be exposed to the virus from humans,” the Penn State study state. “These include through feeding in backyards or even when a susceptible deer may come in contact with potentially infectious material (saliva, urine, etc.) from an infected human in forested areas or exurban environments.”
Dr. Jennifer Ramsey, wildlife veterinarian for Montana’s Department of Fish, Wildlife and Parks said this is the first potentially widespread outbreak of a “reverse-zonoses” she’s encountered during her career.
“No one knows yet how that transmission’s occurring, whether it’s coming through some sort of direct contact, or is somehow being transmitted from humans out into the environment and then on to deer,” Ramsey said. “That’s a big question that folks are going to be trying to figure out.”
Ramsey said wildlife biologists in Montana have not yet begun sampling the state’s white-tail deer population for the SARS-CoV-2 antibody, but that Montana FWP researchers would be cooperating with the USDA in a national surveillance study of COVID-19 in deer scheduled to take place next hunting season.
“Hunting season is our best opportunity to get our hands on a lot of hunter-harvested deer samples,” she said.
Ramsey added that hunters and meat processors should always exercise caution when handling wild game.
“There’s potential for zoonotic diseases in any animal, whether your hunting or trapping or a rancher handling,” she said. “Handling the respiratory tract during field dressing would probably present the best opportunity for exposure. There’s just a lot we don’t know yet about this particular virus and how likely it is to be transmitted from an infected deer to a human.”
Can COVID-19 infected deer spread the virus to humans?
There is no evidence that animals, including deer, are playing a significant role in the spread of COVID-19 to people; however, that possibility has not been ruled out. Based upon the limited amount of information currently available, the risk of white-tail deer spreading COVID-19 to people is low; however, more research is needed.
Do deer show clinical signs of COVID-19?
Thus far there have been no reports of clinical illness associated with COVID-19 in the deer populations that were surveyed, and clinical signs of COVID-19 have not been observed in wild white-tailed deer.
Can other animals besides white-tail deer contract COVID-19?
Recent experimental research shows that many mammals, including cats, dogs, voles, ferrets, bats, hamsters, mink, pigs, rabbits, raccoons and shrews can all be infected with the COVID-19 virus. In December, three snow leopards at the Lincoln Children’s Zoo in Nebraska died of complications from the virus. The nation of Denmark culled 17 million minks in November in response to Covid-19 outbreaks at more than 200 mink farms.
Is hunter-harvested game meat safe to eat?
There is no evidence that people can get COVID-19 by preparing or eating meat from an animal infected with COVID-19, including wild game meat hunted in the United States. However, hunters can get infected with many other diseases when processing or eating game.
How can I protect myself and my family?
Do not allow contact between wildlife and domestic animals, including pets and hunting dogs. • Do not harvest animals that appear sick or are found dead. • Keep game meat clean and cool the meat down as soon as possible after harvesting the animal. • Avoid cutting through the backbone and spinal tissues and do not eat the brains of wildlife. • When handling and cleaning game wear rubber or disposable gloves and do not eat, drink, or smoke. • When finished handling and cleaning game wash your hands thoroughly with soap and water.
Clean knives, equipment, and surfaces that were in contact with game meat with soap and water and then disinfect them. Cook all game meat thoroughly (to an internal temperature of 165°F or higher). Check with your State wildlife agency regarding any testing requirements for other diseases and for any specific instructions regarding preparing, transporting, and consuming game meat.