Widespread infection found in Iowa deer, new study says
A new study of hundreds of white-tailed deer infected with the coronavirus in Iowa has found that the animals probably are contracting the virus from humans and rapidly spreading it among one another, according to researchers.
Up to 80% of deer sampled from April 2020 through January 2021 in the state were infected, the study indicated.
Scientists said the findings pose worrisome implications for the spread of the coronavirus, although they were not able to identify how the deer might have contracted the virus from humans. There is no evidence that deer have passed the virus back to humans.
Researchers and outside experts characterized the study’s findings as a troubling development in the course of the pandemic. Widespread infection among North America’s most ubiquitous game species could make eradicating the pathogen even more difficult, especially if they became a reservoir for mutations that eventually spill back to humans.
The study has not been published in a peer-reviewed science journal yet, but its authors at Penn State University and wildlife officials in Iowa found the results so disturbing that they are alerting deer hunters and others who handle deer to take precautions to avoid transmission.
This year a multistate survey of white-tailed deer by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service turned up antibodies for the virus among less than half the deer in four states, but that study confirmed exposure, not infection. (The presence of antibodies suggests the deer fought off infection.)
This new analysis — conducted by examining the lymph nodes of samples from roadkill and from those felled by hunters — showed active infections, the researchers said. The veterinary microbiologists who led the Penn State study, Suresh Kuchipudi and Vivek Kapur, said they were not prepared to find such widespread infection.
“It was effectively showing up in all parts of the state,” Kuchipudi said. “We were dumbfounded.”
Evidence of transmission from people, the scientists said, was found in the genomic sequencing of the samples collected over months that reflected the virus lineages circulating among humans.
“There is no reason to believe that the same thing isn’t happening in other states where deer are present,” Kapur said.
Previous studies have hinted at such a possibility because some other animals are susceptible to infection with SARS-COV-2, the virus that causes COVID-19 in humans. They include ferrets and primates that have been intentionally infected in lab experiments, zoo animals that caught the virus from their handlers and captive mink that were sickened after being exposed to the pathogen by farmworkers.
In the case of mink, the coronavirus has demonstrated an ability to sicken animals infected by humans, and last year, Denmark slaughtered its entire population of 17 million farmed mink after scientists discovered they could pass the virus back to people. The virus, they found, also picked up mutations along the way, but officials said none were especially worrisome.
The findings were verified last week by federal scientists at the National Veterinary Services Laboratories, according to a spokesperson.
Scientists who reviewed the findings said they were not entirely surprised.
“If deer can transmit the virus to humans, it’s a game-changer,” said Tony Goldberg, a veterinarian at the University of Wisconsin who studies the evolution of infectious diseases as they jump between animals and people. “To have a wildlife species become a reservoir after transmission from humans is very rare and unlucky, as if we needed more bad luck.”
The Penn State researchers have been working with the Iowa Department of Natural Resources, which conducts surveillance on chronic wasting disease, a fatal neurological illness among white-tailed deer. The first positive test results showed up in September 2020 — in two deer at different ends of the state. From late November to early January, as the pandemic was surging in humans across Iowa, 80% of the deer specimens tested positive for the virus.
By then the researchers had tested only 300 of the 5,000 lymph nodes available to them, but the evidence was overwhelming.
Such a high rate of infection, Kuchipudi said, was effectively 50 times greater than its prevalence among Iowa’s human residents during the peak of the pandemic.
What they found as they probed deeper was even more astounding. Using tests to decode the genomic makeup of each viral sample, they found similar patterns between the emergence of mutations and variants in the state’s deer population and those infecting people.
The study’s authors say it is unclear whether the deer were sickened by the infection.
In the meantime, several states have advised deer hunters to take precautions when dealing with whitetailed deer: Wear rubber gloves and perhaps a mask when field dressing and processing, sanitize hands and instruments after dressing, and bag carcass remains before disposing in trash. Health officials say eating cooked venison carries little risk as long as it reaches an internal temperature of 165 degrees Fahrenheit.