By that time, five other countries in the European Union, plus Canada, had also recorded cases in mink farms, but they were no longer the only places affected. In August, the coronavirus was identified in mink from fur farms in Utah, and by October 10,000 of them had deceased. By December, the virus had also invaded farms in Michigan, Oregon and Wisconsin. (Unlike Europe, American fur producers did not kill their mink.)
The original overflow had been the initial transfer from the bat to the mysterious animal to humans. The fallout went the other way, from humans to animals – into hundreds of thousands of members of a different species than those that had previously given the virus a place to adapt. That many mink, living in close quarters, could provide SARS-CoV-2 with a huge opportunity to mutate in unpredictable ways. At the end of last year, this possibility was confirmed. In Danish mink, a viral variant appeared which had a group of previously unrecorded mutations, changes that allowed the virus to escape some of the immune protection conferred by neutralizing antibodies.
The fallout is inherently troubling – but it may not be a public health hazard if a virus returns to an animal population but does not spread further from there. A survey in the Netherlands last summer found a small number of farm workers carrying versions of the virus that, after genomic analysis, had clearly passed through the mink first. Mink on these farms, stressed by confinement and overcrowding, could be particularly vulnerable to the virus and, therefore, themselves and their owners could together form a unique hotspot. Anticipating this, two European health agencies advised At the start of the month, farm mink and farm workers are regularly tested frequently to see what viruses might be circulating on the farms.
But what if the virus passed not between a confined species and its masters, but into wild members of that species or other unrelated ones? This scenario haunts veterinarians and public health officials, and it may have happened.
In December, the USDA found the virus in a wild mink in Utah that was trapped near a fur farm. Presumably, he acquired the virus by coming into contact with mink kept on the farm, or with farm debris, or even with an escaped animal; USDA officials said no other wildlife trapped and tested in the area carried the virus. But the possibility that other wildlife may acquire the virus troubles scientists. This could include those that are closely related to mink (such as ferrets), other animals in the same family (such as weasels or otters), or even those that are unrelated.
“This is something we have to be very concerned about, and not just because it could create an alternate reservoir that could then be a source for humans,” says Raina Plowright, disease ecologist and veterinarian and associate professor at Montana. State University. “In each reservoir there will be different selective pressures on the pathogen, so the virus will evolve in different ways to overcome the barriers present within that species. If we start circulating coronaviruses in different species, all with slightly different genotypes, then we also have the possibility of new coronaviruses emerging that might be different enough from the current one to escape vaccine-induced immunity. .
These alternative hosts could be bats, the apparent home of coronaviruses. Last September, a team of researchers from several institutions valued that up to 40 species of North American bats could be susceptible to infection and could serve as viral reservoirs. It could mean non-human primates, too: Johnson, whose NIH-funded project is working in South America, is worried about possible virus trafficking between humans and forest monkeys.