The analysis by Penn State and Iowa researchers strongly indicates that deer are getting the virus from humans, worrying experts about a deep wild reservoir for the virus.

By Andrew Jacobs

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 then rapidly spreading it among one another, according to researchers.

Up to 80 percent 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 spilled back over 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.

Earlier 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. (Antibodies could mean 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,” said Dr. Kuchipudi. “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,” Dr. Kapur said.

Previous studies have hinted at such a possibility because a number of 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 farm workers.

In the case of mink, the coronavirus has already 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, had also picked up mutations along the way, but officials said none were especially worrisome.

If the virus were to become endemic in wild animals like deer, it could evolve over time to become more virulent and then infect people with a new strain capable of evading the current crop of vaccines.

The findings were verified on Tuesday by federal scientists at the National Veterinary Services Laboratories, according to a spokesperson.

Scientists unaffiliated with the study who reviewed the findings said they were stunned, but 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-Madison 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.”

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