California detects first case of COVID infection in wildlife

The finding in a deer in El Dorado County, announced by California Department of Fish and Wildlife, adds to the growing concern by scientists that animals could act as a hiding place for the virus, perhaps breeding dangerous variants that cause new outbreaks in people.

The COVID virus has been found in a deer in the Sierra Nevada, representing the first detection of the pathogen in California’s free-ranging wildlife.

The discovery, revealed in a new analysis of a sample from a mule deer buck collected in 2021, has no immediate consequence for people. There is already much human-to-human transmission, and vaccines largely protect us.

But the finding, announced by the California Department of Fish and Wildlife, adds to the growing concern by scientists that animals could act as a hiding place for the virus, perhaps breeding dangerous variants that cause new outbreaks in people.

“We expected that if we looked for this virus, we’d find it,” said Dr. Brandon Munk, senior wildlife veterinarian with the California Department of Fish and Wildlife. “But the bottom line is: We don’t yet know what any of it means.”

Previous research has revealed that the virus can also lurk in cats, dogs and zoo animals, as well as deer in other states.

There’s evidence, although still no proof, that an animal sold at a market in Wuhan, China, in late 2019 spread the virus to people, igniting the global pandemic.

And outbreaks in mink farms in the Netherlands have shown that infected animals can transmit the virus to humans.

A related but far more deadly virus, called Middle East Respiratory Syndrome (MERS)-CoV, lives in camels. When it jumps to humans, it has a fatality rate of 9.5% to 34.4%. By comparison, COVID’s fatality rate is 1.1%, according to the Johns Hopkins Coronavirus Resource Center.

The good news is the virus does not appear to cause illness in deer and is not considered to be a threat to the state’s estimated 445,000 mule deer, social creatures that are named for their large ears.

The virus was detected in lymph nodes taken from the neck of a dead deer in El Dorado County, hunted and on its way to be turned into venison. Lab tests found the Delta B.1.617.2 variant, which was circulating in humans at the time. The discovery was made during part of the state’s regular wildlife surveillance effort to track the spread of infectious diseases.

Test specimens were taken from 170 black-tailed and mule deer collected in 2020 and another 209 black-tailed and mule deer collected in 2021. Testing was conducted by the California Animal Health and Food Safety Laboratory at UC Davis, with confirmation provided by the U.S. Department of Agriculture’s lab in Ames, Iowa. The El Dorado deer was the only tested animal in California infected with COVID.

Results were delayed because the usual approach to sample processing had to be modified, said Monk.

In addition, wildlife veterinary labs are stretched thin by the demands of more catastrophic potential outbreaks, such as avian influenza and botulism in birds, hemorrhagic disease in rabbits or chronic wasting disease in deer and elk.

Nevertheless, COVID is beginning to show up in deer across the country with more regularity.

Wildlife officials in Utah recently announced that a November-December 2021 field study had detected the first case of SARS-CoV-2 in mule deer.

Two weeks ago, a study led by Sarah Bevins, a research biologist at the National Wildlife Research Center in Fort Collins, Colorado, showed SARS-CoV-2 occurrence in white-tailed deer throughout much of their range in the United States.

Of 11,113 white-tailed deer samples from 29 states and Washington, D.C., collected from November 2021 to October 2022, 12.2% showed evidence of the virus and 31.6% had antibodies.

“This is an unexpectedly high level of infection for a recently emerged pathogen that has now spilled-over from people to wildlife,” the study concluded.

Comparisons of the viral genetic lineages suggest that human-to-deer transmission is occurring repeatedly, followed by deer-to-deer transmission.

Scientists know that many animals, not just humans, have the protein that allows the COVID virus to infect cells. Called the angiotensin-converting enzyme 2, or ACE2 “receptor,” the protein provides the entry point for the coronavirus to hook into and enter a cell.

But infectious disease in wildlife is more poorly understood than in humans because there are so many different species to study. Each species may respond differently to the COVID virus.

It’s a mystery how California’s deer were exposed to COVID.

Mule deer live in close proximity to people in towns across California. Some people feed deer, so the virus could have spread through the air or through food handling. Or they may have been exposed while in a rehabilitation program that cares for deer that are injured or orphaned by car accidents, then released in the wild. Perhaps deer in captivity had contact with wild deer, transmitting the virus.

“This is certainly another reminder not to intentionally feed deer,” said Munk. “Artificially congregating deer increases the likelihood of spreading disease and may be a source of SARS-CoV-2 exposure for deer.”

There’s no evidence yet that the virus can spread to other wild species, such as elk, or to domestic livestock such as horses and cattle.

“We continue to work with partners to better understand what, if any, significance SARS-CoV-2 infections in wildlife may pose to wildlife and people,” said Munk.