The decision this past week by the Danish government to kill millions of mink because of coronavirus concerns, effectively wiping out a major national industry, has put the spotlight on simmering worries among scientists and conservationists about the vulnerability of animals to the pandemic virus and what infections among animals could mean for humans.

The most disturbing possibility is that the virus could mutate in animals and become more transmissible or more dangerous to humans. In Denmark, the virus has shifted from humans to mink and back to humans, and has mutated in the process. Mink are the only animals known to have passed the coronavirus to humans, except for the initial spillover event from an unknown species. Other animals, like cats and dogs, have been infected by exposure to humans, but there are no known cases of people being infected by exposure to their pets.

The versions of the virus that have mutated in mink and spread to humans are not more transmissible or causing more severe illness in humans. But one of the variants, found in 12 people so far, was less responsive to antibodies in lab tests. Danish health authorities worried that the effectiveness of vaccines in development might be diminished for this variant and decided to take all possible measures to stop its spread. This included killing all of the country’s mink and effectively locking down the northern part of the country, where the mutated virus was found.

Mink are not the only animals that can be infected with the coronavirus. Dogs, cats, tigers, hamsters, monkeys, ferrets and genetically engineered mice have also been infected.

Dogs and cats, including tigers, seem to suffer few ill effects. The other animals, which are used in laboratory experiments, have exhibited varying responses. Farmed mink, however, have died in large numbers in Europe and in the United States, perhaps partly because of the crowded conditions on those ranches, which could increase the amount of exposure.

Public health experts worry that any species capable of infection could become a reservoir that allowed the virus to reemerge at any time and infect people. The virus would likely mutate in other animal species as it has been shown to do in mink. Although most mutations are likely to be harmless, SARS-CoV-2 conceivably could recombine with another coronavirus and become more dangerous.