Studies find that animal coronaviruses can infect people

A white-tail deer.  A Canadian study has identified one case of deer-to-human transmission of SARS-CoV-2, the virus that causes COVID-19.

A white-tail deer. A Canadian study has identified one case of deer-to-human transmission of SARS-CoV-2, the virus that causes COVID-19.

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There are only seven coronaviruses known to infect people, including three that have triggered epidemics in the past two decades: SARS, MERS and SARS-CoV-2, which causes COVID-19.

But University of Florida scientists say they found evidence that some coronaviruses previously known to infect only animals have crossed the species barrier, spreading from pigs and dogs to people.

The findings, reported in two separate studies published in October and November 2021, raise concerns about the potential evolution of new strains of coronaviruses capable of causing severe disease in humans. They also have upended long-held beliefs among scientists about the behavior of coronaviruses, said J. Glenn Morris, an infectious disease physician and a co-author of both studies.

“We have always worked on the assumption that there were really only a small handful of coronaviruses that were capable of infecting humans,” he said. “There’s a few that cause the common cold, then SARS, SARS-CoV-2 and MERS. But it felt like we didn’t need to worry about all those other coronaviruses out there, and coronaviruses are extremely common in animals.”

Coronavirus jumped from dogs, pigs to humans

The animals cited in the studies are pigs and dogs. In both studies, the children and adults infected with the animal viruses reported fever and mild illness, suggesting that the strains do not pose a major human health threat. But the potential for new strains to develop or acquire the genes needed to cause severe illness in people is a concern.

Morris, who is also director of UF’s Emerging Pathogens Institute, which studies new and re-emerging diseases, said he’s no longer certain there’s a hard line between species when it comes to coronaviruses.

“What our data is starting to show … is that strains from animals are able to move into humans, and there are probably a lot of animal strains that move into humans,” he said. “We weren’t looking that hard, and we picked up two different instances, and I think if we really started looking, then what we would begin to find is that movement of coronaviruses from animals into humans and from humans into animals actually occurs not infrequently.”

VIRUS PIGS EUTHANIZED 1
University of Florida scientists say they found evidence that some coronaviruses previously known to infect only animals have crossed the species barrier, spreading from pigs and dogs to people. Jenn Ackerman The New York Times

Canine coronavirus found in pneumonia patients

All of the cases reported in the two studies occurred in Haiti before the COVID-19 pandemic. UF scientists had taken and stored blood and urine samples from people who had reported fever and mild illness in 2014, 2015 and 2017. They decided to test the old specimens after a study published in May 2021 reported that physicians had identified canine coronavirus in pneumonia patients hospital in 2017 and 2018 in Sarawak, Malaysia.

The first study analyzed a urine sample from a UF medical team member who developed “fever and malaise” after returning from a mission trip to Haiti in March 2017. Researchers found that the virus showed 99.4% similarity with the canine coronavirus identified in the pneumonia patients in Malaysia — suggesting that the virus or a similar mutation occurred in multiple locations.

The second study found evidence of so-called porcine deltacoronavirus infection in three Haitian children whose blood samples had been taken in 2014 and 2015 at a free school clinic where UF doctors were monitoring illnesses among children seen at the clinic in the Gressier region of Haiti.

The children’s symptoms included fever and mild illness. But there are few clues about how far the porcine deltacoronavirus spread or how it was introduced to Haiti, Morris said.

Adding to the mystery is the fact that scientists identified two distinct strains of porcine deltacoronavirus in the infected children — one they traced to China, and a second to the United States.

Minks, white-tailed deer spread virus to people

Although scientists have found SARS-CoV-2 in 29 kinds of animals, including white-tailed deer, cats, dogs, ferrets, mice, otters and tigers, in most cases the animals have not been shown to spread the virus to people. In November 2020, scientists found that minks have spread the virus to people, and a Canadian study that has yet to be published in a peer-reviewed journal reported identifying one case of deer-to-human transmission of SARS-CoV-2.

For scientists like Morris, the findings that the pandemic will continue to be unpredictable, at least in part because coronaviruses mutate so rapidly.

“What we see is this constant ongoing movement, swirling of different strains, infections, genetic material, movement from animals to humans and humans to animals,” he said. “This is all going on and it gets back to: Are we going to be able to establish a stable endemicity? Maybe, but there are a lot of things that could create problems.”

This story was originally published June 9, 2022 6:00 AM.

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Daniel Chang covers health care for the Miami Herald, where he works to untangle the often irrational world of health insurance, hospitals and health policy for readers.

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