Why mink farmers are in next phase
Vaccine may prevent virus jumping to animals
Mink farmers, a small sliver of the Wisconsin population, are set to be among those offered the COVID-19 vaccine next — a choice that might seem surprising.
Teachers, food chain workers, public transit employees, 911 dispatchers and prisoners and corrections workers are the other Wisconsin residents among roughly 1.6 million who are tentatively expected to get their shots beginning March 1, according to guidelines released Tuesday from the state Department of Health Services.
Meanwhile, the state is still pushing to deliver vaccines to health care workers, assisted living staff and residents, police and firefighters, and people over 65.
Why are mink farmers up next? Mink pose a biosecurity risk, said Stephanie Schauer, Wisconsin’s immunization program manager. If the virus runs rampant through thousands of mink, it won’t just kill many of them, but it could also spread to other animals or even back to humans.
Just like humans, mink are particularly susceptible to COVID-19, said Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory at the University of Wisconsin-Madison.
Mink are members of the Mustelidae family, which also includes ferrets, weasels, badgers, otters, marten and wolverines. Receptors in their lungs that are similar to those in humans are adept at “grabbing” the virus to allow it to start replicating, Poulsen said — separating them from other animals, like cows, who do not seem to be as much at risk of being infected.
For mink, the virus can spread fast and have devastating consequences. It’s not yet known why the animals get so sick, but their living conditions might result in exposure to higher levels of the virus — they can’t exactly practice social distancing, because tens of thousands of farmed mink live close to each other in small cages.
Wisconsin is the top producer of mink pelts in the U.S. — in 2019, the state produced more than a million of the nation’s 2.7 million pelts, which were worth over $59 million, according to the U.S. Department of Agriculture.
That leaves us more vulnerable to COVID-19 outbreaks in the mink population. Last fall, outbreaks surfaced at two of the state’s 19 mink farms, in Taylor County. More than 5,000 animals died after the virus was believed to have
jumped from a human worker to one of the animals.
Poulsen said he’s impressed that the state’s mink cases were kept to those two farms. It could have been much worse.
In Denmark, a now-infamous example of how serious a virus outbreak among the animals can be, millions of mink were slaughtered to ward off further spread of infection (some of which resurfaced from their graves because of the gases produced by their decay).
But Denmark’s health officials weren’t just worried about mink dying off. They were also concerned about the virus jumping from mink back to humans. Each time the virus infects a new person (or animal), it presents a new opportunity for a change, or mutation, in its genetic code. Viruses mutate regularly during their lifespan, and many of the mutations don’t have any real effect, but — as we’ve seen with the new, more contagious variants that have taken over transmission in the U.K., South Africa and Brazil — every once in awhile, they can pose a new threat.
If you give the virus a chance to get tens of thousands of mink sick, for example, that’s many more opportunities for one of those threatening mutations to occur. And once the mutations arise, they could be passed back to humans. Such mutations could also pose a problem in the worldwide vaccination campaign.
In Denmark, a specific variant arise from the rapid transmission among mink and was identified in a dozen people, too, prompting the government to put over a quarter of a million residents in the northern part of the country on lockdown.
Luckily, that variant didn’t appear in the Taylor County mink, Poulsen said.
A multi-state team including his lab, public health departments, the Centers for Disease Control, U.S. Department of Agriculture, Wisconsin’s Department of Agriculture, Trade and Consumer Protection have been working since March to sequence samples of the virus from mink who tested positive, just like we do with human samples, which helps identify variants and track how the disease has spread over time.
Besides passing the virus back to humans, mink could also pass it to wild animals, setting up the possibility that COVID-19 could entrench itself in the wildlife population and come back to reinfect humans at a later date. Diseases are extremely difficult to control in wild populations, Poulsen explained, because unlike domestic animals, we don’t know where wild animals go.
An instance of this has already been documented in Utah, where a wild mink tested positive for the virus.
Wisconsin mink farmers encompass a small portion of the state’s population — a few hundred people, Schauer said — and are eligible for their shots beginning March 1, unless more supply of vaccine makes it possible earlier.