In late September of 2020, captive mink on a farm in Michigan suddenly fell ill. They stopped eating, struggled to breathe and bled from the nose, according to a report from the World Organization for Animal Health. Two thousand animals died.
Laboratory testing soon confirmed that the mink were infected with the coronavirus.
The Centers for Disease Control and Prevention dispatched a team of outbreak investigators, who collaborated with other agencies to swab mink, farm workers and a menagerie of other animals, from rats to raccoons, to determine how the virus had spread.
“We tried to leave no stone unturned,” said Dr. Casey Barton Behravesh, who directs the C.D.C.’s One Health Office.
Last month, the C.D.C. confirmed that four Michigan residents, including two farm employees, had been infected with the same unique coronavirus variant that was found in the mink. It was the first, and so far only, known instance of possible animal-to-human transmission in the United States.