March 25, 2021 -- The new coronavirus variants are not just problems for humans.
New research shows they can also infect animals, and for the first time, variants have been able to infect mice, a development that may complicate efforts to rein in the global spread of the virus.
In addition, two new studies have implications for pets. Veterinarians in Texas and the United Kingdom have documented infections of B.1.1.7 — the fast-spreading variant first found in the U.K. — in dogs and cats. The animals in the U.K. study also had heart damage, but it's unclear if the damage was caused by the virus or was already there and was found as a result of their infections.
Animal studies of coronavirus and its emerging variants are urgent, Sarah Hamer, DVM, a veterinarian and epidemiologist in the Texas A&M University's College of Veterinary Medicine and Biomedical Sciences in College Station, says.
She's part of a network of scientists who are swabbing the pets of people who are diagnosed with COVID-19 to find out how often the virus passes from people to animals.
The collaboration is part of the CDC’s One Health initiative. One Health aims to tackle infectious diseases by recognizing that people can't be fully protected from pathogens unless animals and the environment are also safeguarded.
"Over 70% of emerging diseases of humans have their origins in animal populations," Hamer said. "So if we are only focusing on studying disease as it emerges in humans and ignoring where those pathogens have been transmitted or circulating for years, then we might miss the ability to detect early emergence. We might miss the ability to control these diseases before they become problems for human health.”
Variants Move to Mice
In new work, researchers at the Institut Pasteur in Paris have shown that the B.1.351 and P.1 variants of concern, which were first identified in South Africa and Brazil, respectively, can infect mice, giving the virus a potential new host.
Older versions of the virus couldn't infect mice because they weren't able to bind to receptors on their cells. These two variants can.
On one hand, that's a good thing, because it will help scientists more easily conduct experiments in mice. Before, if they wanted to do an experiment with coronavirus in mice, they had to use a special strain of mouse that was bred to carry human ACE2 receptors on their lung cells. Now that mice can become naturally infected, any breed will do, making it less costly and time-consuming to study the virus in animals.
On the other hand, the idea that the virus could have more and different ways to spread isn't good news.
"From the beginning of the epidemic and since human coronaviruses emerged from animals, it has been very important to establish in which species the virus can replicate, in particular the species that live close to humans," said Xavier Montagutelli, DVM, , head of the Mouse Genetics Laboratory at the Institut Pasteur. His study was published as a preprint ahead of peer review on BioRXIV.
Once a virus establishes itself within a population of animals, it will continue to spread and change and may eventually be passed back to humans. It's the reason that birds and pigs are closely monitored for influenza viruses.
So far, with this coronavirus, only one animal has been found to catch and spread the virus and pass it back to people — farmed mink. Researchers have also documented coronavirus antibodies in escaped mink living near farms in Utah, suggesting the virus has the potential to be transmitted to wild populations.
And the move of the virus into mice suggests that the virus could establish itself in a population of wild animals that live close to humans.
"At this point, we have no evidence that wild mice are infected, or can become infected from humans," Montagutelli said. He added that his findings emphasize the need to regularly test animals for signs of the infection. He said these surveys will need to be updated as more variants emerge.
"So far, we've been lucky that our livestock species aren't really susceptible to this," said Scott Weese, DVM, a professor at Ontario Veterinary College at the University of Guelph in Canada, who studies emerging infectious diseases that pass between animals and people.
While the outbreaks on mink farms have been bad, imagine what would happen, Weese said, if the virus moved to pigs.
"If this infects a barn with a few thousand pigs — which is like the mink scenario — but we have a lot more pig farms than mink farms," he said.
"With these variants, we have to reset," he said. "We've figured all this about animals and how it spreads or how it doesn't, but now we need to repeat all those studies to make sure it's the same thing."
Pets Catch Variants, Too
Pets living with people who are infected with SARS-CoV-2 can catch it from their owners, and cats are particularly susceptible, Weese said.
Contact tracing studies, which also tested animals for signs of the virus, have found that somewhere between 20% and 50% of cats living with infected people have signs of infection, while 20%-30% of dogs were infected.
"It's quite common," for pets to get COVID, Weese said.
Now, two new studies have shown that fur babies can also be infected by the newer B.1.1.7 variant.
The first study, from researchers at Texas A&M, documented the variant in a dog and a cat from Brazos County, Texas. Neither the older black Lab mix or the older domestic shorthair cat had symptoms of COVID-19. They were tested as part of a project funded by the CDC.
Weese said pets are at risk by people who are infected, but they don't seem to play a big role in spreading the disease to humans. So if you have pets, there's no reason to worry that they could bring the virus home to you. You're more likely to be a risk to them.
The second study, from a specialty animal hospital in southeast England, documented infection by the B.1.1.7 virus variant in 11 dogs and cats. Most of the pets had unusual symptoms, including inflamed hearts and heart damage.
Weese called this study interesting and said its findings deserve more investigation, but he pointed out that the study can't determine whether the infection caused the heart damage, or whether it was already there.
"This is a human virus. There's no doubt about it. It can affect other species, but it likes people a lot better," he said.
"If you think about the big picture and what is the potential role of animals, pets are pretty low risk," he said.