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Bats, humans, monkeys, mink, big cats, and great apes – the coronavirus can become established in many different animals. But now the list of potential hosts has expanded to include mice, according to a baffling new study.
Infected rodents pose no immediate risk to people, even in cities like London and New York, where they are ubiquitous and unwanted in subway stations, basements and backyards.
However, the finding is worrying. Along with previous work, this suggests that new mutations give the virus the ability to replicate in a wider range of animal species, experts said.
“The virus evolves and unfortunately it does quite quickly,” said Timothy Sheahan, a virologist at the University of North Carolina at Chapel Hill, who was not involved in the new study.
In the study, the researchers introduced the virus into the nasal passages of laboratory mice. The form of the virus first identified in Wuhan, China, cannot infect laboratory mice, nor B.1.1.7, a variant that has spread across much of Europe, have discovered the researchers.
But B.1.351 and P1, the variants discovered in South Africa and Brazil, can replicate in rodents, said Dr Xavier Montagutelli, veterinarian and mouse geneticist at the Institut Pasteur in Paris, who led the study. The research, posted online earlier this month, has yet to be reviewed for publication in a scientific journal.
The results only indicate that infection in mice is possible, said Dr Montagutelli. Mice captured in the wild have not been found infected with the coronavirus, and so far the virus does not appear to be able to pass from humans to mice, mice to humans, or mice to mice.
“What our results underscore is that there is a need to regularly assess the range of species that the virus can infect, especially with the emergence of new variants,” said Dr Montagutelli.
The coronavirus is believed to have originated in bats, with possibly another animal acting as an intermediate host, and scientists fear the virus could revert to what they describe as an animal “reservoir”.
In addition to potentially devastating these animal populations, a coronavirus spreading into another species can then acquire dangerous mutations, returning to humans in a form that current vaccines were not designed to repel.
Mink are the only animals known to be able to catch and transmit the coronavirus from humans. In early November, Denmark slaughtered 17 million farmed mink to prevent the virus from transforming into dangerous new variants in animals.
More recently, researchers have found that B.1.1.7 infections in domestic cats and dogs can cause heart problems in pets similar to those seen in people with Covid-19.
To establish a successful infection, the coronavirus must bind to a protein on the surface of animal cells, enter the cells, and harness their machinery to make copies of itself. The virus must also escape the first attempts of the immune system to thwart the infection.
Given all of these requirements, it is “quite extraordinary” that the coronavirus can infect so many species, said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases. “Generally, viruses have a narrower host range.”
Mice are a known reservoir for hantavirus, which causes a rare and fatal disease in humans. Even though the coronavirus variants do not appear to be able to switch from mice to humans, it is possible that they will spread among rodents, evolve into new variants, and then infect people again, Dr Munster said.
Variants can also threaten endangered species like blacklegged ferrets. “This virus seems to be able to surprise us more than anything else, or any previous virus,” Dr Munster said. “We have to be careful.”
Dr Sheahan said he was more concerned with transmission to people from farm animals and pets than from mice.
“You don’t catch wild mice in your house and snuggle up – you put your nose up and share the same airspace, like maybe with your cat or dog,” he said. “I would be more worried about the wild or domestic animals we have a more intimate relationship with.”
But he and other experts said the results underscored the need to closely monitor rapid changes in the virus.
“It’s like a moving target – it’s crazy,” he added. “There is nothing we can do about it, other than trying to get people vaccinated very quickly.”
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