that the virus had mutated as it moved among the mink and that the animals then spread the altered virus back to humansall of that jumping back and forth over the fence is what we saw said dr marion koopmans a virologist at erasmus university medical center in rotterdam and thats something that as a virologist you dont really likethe netherlands and denmark took quick and decisive action said adriana diaz a doctoral student at the university of london who studied these responses dutch authorities conducted antibody testing on all farms and required farmers to report respiratory symptoms in mink and regularly submit carcasses for examination still the virus proved difficult to control and both nations ultimately shuttered their mink farmsthe united states took a different tack developing a set of voluntary guidelines to help farmers keep the virus at bay including asking farm workers to wear masks and notifying authorities of suspected casesbut there was no national screening program and federal officials relied upon farm owners to selfreport outbreaks all of our federal surveillance efforts are voluntary said dr tracey dutcher the science and biodefense coordinator for the animal and plant health inspection service at the united states department of agriculturethe cdc investigated outbreaks only when officially invited some owners of affected farms declined to participate and field teams only performed onsite investigations on eight farms dr barton behravesh saidon the michigan farm cdc investigators worked with the usda and state agencies to test humans and animals for the virus they collected swabs and samples from 159 mink on the farm all but two were actively infected dr barton behravesh saidnone of the other animals tested around the farm two dogs a cat raccoons opossums striped skunks rats groundhogs and rabbits were infected but one dog tested positive for antibodies officials saidtwo of the farms employees were infected with the same version of the virus that was spreading among the mink the variant had two mutations that had also been found in farmed mink in europe and in people connected to mink farmsofficials found the same mutations in a sample collected from another michigan resident nearly two months after the mink outbreak and then in a fourth person connected to that resident the third case was a local taxidermist according to internal health department emails obtained by the documenting covid19 project and the detroit free press and the fourth case was the mans wife the organizations later reported michigans department of health human services declined to confirm these details for privacy reasons neither had any known connection to the mink farmunanswered questionsimagecreditsergio flores for the new york timesthese findings suggest a likely scenario experts said a person passed the virus to the mink and the mutations emerged as the virus spread among the animals which then transmitted them back to the farm workers we concluded that there was likely minktoperson spread on this particular michigan farm dr barton behravesh saidbut determining when and in whom the mutations first