Washington, Apr 19 (IANS): At least four Americans were infected with a version of Covid virus, seen majorly in mink in 2020, likely becoming the first spillover cases in the country, the US Centers for Disease Control and Prevention (CDC) has said.

The infected people are from Michigan -- two employees of a Michigan mink farm that experienced a coronavirus outbreak in October 2020 -- while the other two had no known links to the farm.

This suggests that the mink variant may have been circulating more widely among area residents at the time, the New York Times reported.

The cluster, which previously included just three cases, represents the first known instance of possible animal-to-human transmission of the virus in the US.

Samples of the virus collected from all four people contained two mutations that scientists have hypothesised may be signs of adaptation to mink, Casey Barton Behravesh, who directs the CDC's One Health Office, told NYT.

The mutations have previously been documented in farmed minks in Europe, as well as in people with connections to those farms.

"This, in addition to the mink farm workers testing positive for Covid-19 after the mink herd had begun experiencing illness and increased mortality, suggests that the most likely hypothesis is that the workers were infected after contact with mink on the farm," Behravesh said.

But that cannot be conclusively proved, she noted.

"Because there are few genetic sequences available from the communities around the farm, it is impossible to know for sure whether the mutations came from mink on the farm or were already circulating in the community," she said.

Mink-to-human transmission has also been reported in Denmark, the Netherlands and elsewhere.

Overall, transmission of the virus from animals to humans is believed to be rare. Humans are far more likely to spread the virus to one another, or to other species, than they are to catch it from animals, experts said.