More than 92,000 minks were ordered killed at the farm in the Aragon region of northeastern Spain, with nine out of 10 animals estimated to have contracted the virus.
After the Dutch outbreaks began in April, professor Wim van der Poel, a veterinarian who studies viruses at Wageningen University and Research, determined that the virus strain in the animals was similar to the one circulating among humans.
“We assumed it was possible that it would be transmitted back to people again,” the virus expert said, and that's what appeared to have happened with at least two of the infected workers.
Richard Ostfeld, a researcher at the Cary Institute of Ecosystem Studies in Millbrook, New York, said that if confirmed, these would be the first known instances of animal-to-human transmission.
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“With the evidence for farmed mink-to-human transmission, we definitely need to be concerned with the potential for domesticated animals that are infected to pass on their infection to us,” Ostfeld said by email.
The US Centers for Disease Control and Prevention says some coronaviruses that infect animals can be spread to humans and then spread between people, but it adds that this is rare.
Both the World Health Organization and the Paris-based World Organisation for Animal Health are studying the transmission of the virus between animals and people.
Several universities and research institutes also are examining the issue.
The WHO has noted that the transmission on the mink breeding farms could have happened both ways.