In the first year of the pandemic, at least four people in Michigan have been infected with a version of the coronavirus seen primarily in mink, the Centers for Disease Control and Prevention confirmed Monday.
The cluster, which previously included just three cases, represents the first known case of possible animal-to-human transmission of the virus in the United States.
Two of those infected were employees of a Michigan mink farm that experienced a coronavirus outbreak in October 2020. The other two had no known links to the farm, suggesting the mink variant may have been circulating more widely among area residents at the time.
Virus samples collected from the four people contained two mutations that scientists hypothesize may be signs of adaptation to mink, Dr. Casey Barton Behravesh, who heads the Office of Single Health, said in an email Monday. from the CDC.
The mutations have previously been documented in farmed mink in Europe, as well as in people with connections to those farms.
“This, in addition to mink farm workers testing positive for COVID-19 after the mink herd began experiencing illness and increased mortality, suggests that the most likely hypothesis is that the workers became infected after contact. with the minks on the farm,” Dr. Barton Behravesh said.
But that cannot be conclusively proven, he noted.
“Because few genetic sequences are available from the communities around the farm, it is impossible to know for sure whether the mutations came from the mink on the farm or were already circulating in the community,” he said.
National Geographic first reported the fourth human case, after obtaining government documents about the mink farm outbreak under the Freedom of Information Act.
Last year, The Detroit Free Press and the Documenting Covid-19 project reported the first three cases, which included the two farmworkers and a taxidermist who had no known connection to the mink farm, according to emails obtained by police. two organizations.
On Monday they reported that the fourth case had been the taxidermist’s wife.
In early October 2020, Michigan officials announced that the virus had been detected in mink at a local farm and that several of the animals had died. At the request of the state, the CDC deployed a team to help investigate the outbreak.
The researchers collected samples from animals and human workers on the farm, as well as from people in the surrounding community, Dr. Barton Behravesh said. In March 2021, the CDC updated its website to note that a “small number of people” had contracted a version of the virus that “contained unique mink-related mutations.”
“This suggests that mink-to-human spread could have occurred,” the agency said, noting that all of the human patients had recovered.
But the first human cases, in two workers at the affected mink farm, were identified on November 4, months before the agency updated its website, National Geographic reported.
“The CDC became aware of genetic sequencing data indicating possible mink-to-human transmission in late 2020,” said Dr. Barton Behravesh.
The agency then worked with other federal and state officials to analyze that data, adding: “Information was posted on the CDC website as soon as it became clear there was a possible spread from mink to humans.”
Mink-to-human transmission has also been reported in Denmark, the Netherlands, and elsewhere.
In general, transmission of the virus from animals to humans is thought to be rare. Humans are much more likely to spread the virus to each other, or to other species, than they are to catch it from animals, experts say.