Scientists have found that 40% of wild deer in parts of the U.S. had neutralizing antibodies for the coronavirus, suggesting COVID-19 spread from humans in what is reportedly the first documentation of widespread exposure to the virus in free-roaming animals.
Researchers from the U.S. Department of Agriculture studied 624 pre- and post-pandemic serum samples from wild deer in five U.S. states for exposure to SARS-CoV-2 and detected antibodies in 152 samples — 40% — from 2021.
“SARS-CoV-2, the virus that causes COVID-19 in humans, can infect multiple domestic and wild animal species. Thus, the possibility exists for the emergence of new animal reservoirs of SARS-CoV-2, each with unique potential to maintain, disseminate, and drive novel evolution of this virus,” the authors wrote in their study, published in bioRxiv last week. “Of particular concern are wildlife species that are both abundant and live in close association with human populations.”
Researchers collected 385 wild white-tailed deer serum samples from Michigan, Pennsylvania, Illinois and New York from January through March of this year.
They also pulled from wildlife sample archives from the USDA’s National Wildlife Disease Program to study 239 wild white-tailed deer samples from 2011 to 2020 from the four states and New Jersey. However, most of the archive samples were from 2018 to 2020.
Of the 2021 samples, Michigan had the highest prevalence of coronavirus antibodies among its white-tailed deer at 67% while Illinois had the lowest at 7%.
Meanwhile, antibodies were detected in 31% of the white-tailed deer from New York and 44% of the deer from Pennsylvania.
Dr. William Schaffner, an infectious disease specialist at Vanderbilt University who was not involved in the study, said the researchers’ findings give a “somewhat startling new aspect” to the epidemiology of COVID-19.
It also raises the question if this wild species could become a reservoir for the virus, continue to multiply and mutate and transmit back to humans, he added.
“This is not just an occasional one-off infection. This is serological evidence that wild deer have fairly widespread infection with COVID-19,” Dr. Schaffner said. “This should be a big surprise to just about anybody. Nobody anticipated this was spreading in a wildlife species.”
The researchers also found antibodies in three deer samples from 2020 and one sample from 2019. However, no antibodies were detected in samples from 2011 to 2018.
Dr. Amesh Adalja, a senior scholar for Johns Hopkins Center for Health Security, noted that humans are passing the coronavirus to other animals and that such incidents don’t “really have a major impact on human health.”
“However, they illustrate how this virus is not something amenable to eradication or elimination because it has hosts other than humans,” said Dr. Adalja, who was not involved in the study.
“Any opportunity that the virus has to transmit and replicate is going to lead to more variants. However, when it comes to the variants it appears that our vaccines are able to do what matters, stop serious disease, hospitalization, and death,” he added. “I don’t think that deer infections are a major concern, but it is important to monitor the virus and all the animal species that it infects to understand how the virus is evolving and what traits are being changed by the mutations that accrue.”
Since the coronavirus pandemic began, SARS-CoV-2 infections have been reported in cats, dogs, gorillas, lions, tigers and farmed minks in cases known as zoonotic spillback.
A wild mink in Utah tested positive for SARS-CoV-2 in December following earlier outbreaks among farmed minks in the U.S., the High Country News reported.
The majority of the animals became ill after contact with people infected with COVID-19 including a small number of pet dogs and cats. A ferret in Slovenia also tested positive for SARS-CoV-2.
“A few other mammals can be infected with SARS-CoV-2, but we don’t yet know all of the animals that can get infected,” the Centers for Disease Control and Prevention said.
While there has not been evidence yet of animals spreading the coronavirus to humans, Dr. Schaffner said the potential exists.
The researchers noted that deer could come into contact with people during numerous occasions such as field research, conservation work, hunting, wildlife tourism and captive cervid operations.
They said their findings show the need for continued and expanded wildlife surveillance to measure the impact the coronavirus has on free-ranging deer. They also suggest monitoring predators and scavengers that interact with deer for SARS-CoV-2.