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The first sign of trouble was that the mink stopped eating, said Hugh Hildebrandt, one of two main mink vets in Wisconsin. Next came coughing and sneezing, lethargy and labored breathing. Hildebrandt had worked with mink for 30 years. He wrote the Merck Veterinary Manual section on mink. But he had never seen anything like this.
Captive mink have a flu season in the fall, just like people — they get it from us, in fact. But what appeared in the two Taylor County, Wisconsin mink farms that saw outbreaks in October was not flu, which tends to sicken the weakest animals. This took out the strongest mink, the mature adult females. Over a few days, it killed hundreds per day and about 5,500 total on the two ranches. It whipped through by coat color, light to dark: The lighter-coat mink, ranch-bred to bring out recessive genes, have long been more delicate.
Five to seven days in, the ranchers thought that most of the mink were going to die, said Hildebrandt. “And they wake up the next morning, and it’s just stopped. They all start eating. They eat more than they ever did before.”
It wasn’t hard to guess the cause. Wisconsin was a coronavirus hotspot from late summer on, and workers at mink ranches had already tested positive. The Wisconsin Veterinary Diagnostic Laboratory in Madison confirmed the suspicion within days. The mink almost certainly got it from farmworkers, a jump called “reverse zoonosis.”
The outbreaks shone light on an industry that has for years operated so discreetly in Wisconsin — the nation’s top pelt producer — that even the officials in charge of animal health didn’t know where all of the state’s 19 mink farms were. Those farms are neither regulated nor licensed by the state.
Officials have caught up fast amid concerns that a mutation of the species-hopping virus could pose danger to humans. In fact, the state just added mink farmers to the category of residents next in line for vaccination along with teachers, child care workers and grocery store employees.
Wisconsin is not, however, contemplating a Denmark-style moratorium on mink farming or industry-wide cull, according to state veterinarian Darlene Konkle. That is a last resort. Wisconsin has yet to find a mink-to-human leap of the virus. And since mink aren’t officially considered livestock, Wisconsin doesn’t compensate farmers whose mink are killed to prevent disease spread, she said.
“It is kind of a balance,” Konkle said. “It would be no small thing to take the Denmark approach and say we’re going to depopulate all the mink farms. Because that’s a situation where you’re taking away somebody’s livelihood. You’re depopulating healthy animals as well as potentially infected ones.”
The mink detectives
The first infections of U.S. farmed mink, in Utah in August, triggered a national investigation involving wildlife and human health experts across local, state, and federal agencies. Their questions: How did the virus get there, where would it go next, and what could it do? In Europe, the virus had spread from farm to farm, and also jumped back to humans.
Then, in mid-December, a wild mink trapped near a Utah mink farm was confirmed to have the virus.
“To our knowledge, this is the first free-ranging, native wild animal confirmed with SARS-CoV-2,” said Thomas DeLiberto and Susan Shriner of the USDA’s Animal and Plant Inspection Service. Soon after that, two more mink — both Oregon farm escapees — also tested positive.
Of all the animals that have been infected with the virus that causes COVID-19, (gorillas, dogs and cats, and a few other mammals), the only species to have suffered large-scale casualties so far is the American mink living on mink ranches around the world.
Since the first mink got sick on a Dutch mink ranch in April, millions of the animals have died or been culled on nearly 400 ranches across Denmark, the Netherlands, Sweden, Lithuania, Greece, Italy, France, Spain and Canada. The United States has seen 16 ranch outbreaks since August: 12 in Utah, two in Wisconsin, one each in Oregon and Michigan as of late January.
“It’s a top priority in human and veterinary diagnostic labs,” said Keith Poulsen, director of the veterinary diagnostic lab. It has been running COVID tests on farmed mink and people, in addition to its usual tests on cows, chickens and other animals, and is now operating from 5 a.m. to 2 a.m. to keep up.
Outbreaks on European mink ranches demonstrated the risks. If the virus managed to establish a reservoir of disease in farmed mink or their wild cousins, it could hamper the fight against the pandemic, harm wildlife, or even threaten ecosystems. Particularly if it mutated along the way into something deadlier, more transmissible or harder for modern medicine to attack.
No disease is an island
Such zoonotic outbreaks happen constantly, and disease reservoirs are everywhere. Raccoons harbor rabies; rodents across the American West harbor the bacterium that causes plague. People are a reservoir of tuberculosis for cattle.
Viruses adapt to new hosts by mutating. Some mutations can help the virus spread faster, worsen the severity of disease, make it harder for the body to fight, or make therapeutics or vaccines less effective. That has come to pass recently: an apparently super-contagious variant first discovered in Britain is expected to become the dominant U.S. strain by March.
No evidence has emerged yet that farmed mink have infected people in the United States, though the investigation is ongoing. In Denmark, which was the world’s biggest mink producer with 17 million animals, hundreds of farms were affected.
There, researchers found the virus passed from people to mink and back again, mutating as it went. Some people got a genetic variant dubbed Cluster-5 that looked extra nasty, because the virus’s spikes had changed in ways that made it harder for monoclonal antibody treatments to recognize the virus, at least in the lab.
By mid-November, Cluster-5 cases had stopped turning up and had, scientists guessed, dead-ended.
The mink variant turned out not as bad as feared — but the next one could be worse.
That is why a state advisory committee of health care experts in January recommended that an estimated 300 mink farm workers be included in the next phase of the vaccine rollout.
“Vaccine should be prioritized for this group to reduce the risk that mink variants with spike-protein mutations will spread from animals to humans and potentially reduce vaccine effectiveness,” they wrote.
The mysteries of mutation
When deciding how much to freak out about a zoonotic virus, the details — like what hosts they prefer, how long they stick around, or how fast they can mutate — make all the difference.
“Some viruses hardly ever change, but a host can remain infected for decades. Others mutate at a furious rate and change to outpace our immune response,” wrote Hon Ip, a virologist at the National Wildlife Health Center in Madison, a lab that has been testing wild animals trapped near mink farms.
Ip and other scientists knew early on that mink might be susceptible to COVID-19, because they share some immune response similarities and a key lung receptor with people.
“We have a pretty extensive infrastructure to be able to do this very, very quickly,” Poulsen said. “We’d been at this super-high alert level. And they (mink farmers) were seeing thousands die per day.”
They knew, too, that Wisconsin had a heck of a lot of mink. Last year it produced a million pelts, one-third of the U.S. total. In the past few years, Taylor County produced the most mink pelts in North America, according to Hildebrandt.
CDC teams began collecting samples from the people and the mink on affected farms, while U.S. Wildlife Services live-trapped wild animals nearby. The two farms that were quarantined would not be released until all their tests were negative, “and we’re sure we’re not making a wildlife reservoir,” Poulsen said.
Tracking who gave what to whom will take some time. “Some of them are very, very clear,” Poulsen said. “People became sick from community-acquired infection, and they gave it to the mink. But that’s not all the cases.”
Mink Princesses gone, but farms remain
A billboard once stood in the middle of Medford, Wisconsin, that proclaimed it the Mink Capital of the World. That crossroads is now the home of the Taylor County Museum, where by coincidence, Mary Schultz of the Taylor County Historical Society, a longtime area resident, just finished curating an exhibit about the annual Medford Mink Festival once held there.
Schultz described the exhibit: a small space, full of mink-covered things. “It was a big thing back in the day,” she said. The weeklong festival, first held in 1964, included a pageant to choose a Miss Medford Mink Princess from among the local high-schoolers.
The pageant included a swimsuit competition, though thankfully no mink bikinis. Many items that would not spring to mind as wanting a bit of fur were made of or topped with a bit of fur, including toothpicks, a toothbrush, a men’s tie and a bowtie, cufflinks and a wallet. “I don’t know who in the world would wear that tie,” Schultz said, amused.
The mink billboard came down, Schultz said, around when the mink festivals stopped, maybe 1979. Today, even in Medford, mink ranches operate quietly, as they have done ever since the anti-fur campaigns of the 1980s.
“There’s a great big mink ranch up on a highway northeast of us,” Schultz said. “There’s no sign out there that says what this is, and I don’t even know who owns it.”
An invisible industry
It was so discreet, in fact, that state vet Konkle had to ask the Fur Commission USA how to reach the state’s 19 mink farms.
Mink are not considered livestock by Wisconsin law. They do not need a license to operate, and the Department of Agriculture, Trade and Consumer Protection does not inspect, register or survey them.
Utah state veterinarian David Taylor said the mink industry has “a little bit of mistrust, because of the fact that they have been targets.” In 1997, animal-rights activists freed 7,000 mink from farms in Iowa, South Dakota and Wisconsin with the goal of crippling the fur industry.
“So they are very, very closed to having any outside people come onto their farms and see their operations,” Taylor said.
With some “creative financing” by the Utah state legislature of CARES Act money, and diplomacy on the part of the government officials, Taylor said, the ranch gates began to open.
“When they’re losing that volume of their business in just literally one week’s time, and they’ve lost 50% of their breeders and several thousand mink, having someone come in and just understand that that’s life-shattering for them — that was what opened up the door for communication,” he said.
The pandemic may even have strengthened the domestic mink industry, said Michael Whelan, executive director of the Fur Commission USA.
“Right now there’s a little bit of optimism amongst farmers, because production levels have come down to a much more sustainable level globally,” Whelan said.
The culling controversy
Animal health authorities in the United States could order mink culls, like in Europe. Wisconsin officials have done so for other outbreaks, like on deer farms stricken with chronic wasting disease, but never for a whole industry. That would require a complex legal process, and a mass quarantine of all farms.
Animal rights groups see the mink outbreaks as another reason to ban the industry. The Humane Society Veterinary Medical Association, in a statement, called farmed mink a “significant public health threat.”
The European situation differs in important ways, the industry says. Denmark had way more mink, and more farms — north of a thousand — in an area “a third the size of Wisconsin” Hildebrandt said, with a lot more people around.
By contrast, Wisconsin’s few farms are mostly in sparsely populated rural areas.
Across Europe, millions of mink have died or been killed, the Dutch hastened a previously planned ban on fur farming, and France announced it would close its last four farms. Meanwhile, China, also the biggest market for mink fur, has seen the European culls as a market opportunity and stepped up breeding.
On the trail of wandering mink
How fluid are the boundaries between mink farms and the wild? Pre-pandemic, American mink that escaped or were intentionally released from European farms were considered some of the most damaging invasive species on the continent. But in North America, there’s not much accounting of how often farmed mink escape or what they have done with themselves. This is partly because American mink already live in the wild, partly because mink farms are not closely regulated, and most of all because very few people have looked.
The few include wildlife disease biologist Jeff Bowman and his colleagues at the Ontario Ministry of Natural Resources, who have long been researching the spread and impact of ranch escapees in their province.
Wild mink are small, chocolate-brown, and bitey. They do not come in sapphire, blue iris, white, palomino or any other color that brings to mind a celebrity baby name, as farmed mink do.
Near Ontario mink ranches, 64% of the mink trapped were either escapees or captive-wild hybrids.
“Our studies showed that there are potential pathways for (disease) spread from farms to other wildlife,” he said.
Wisconsin Department of Natural Resources officials haven’t studied the issue of mink farm escapees like Canadian researchers have, though investigators are now considering more surveillance.
But Arnold Groehler, president of the Wisconsin Trappers Association, said he has been catching the odd mink-ranch escapee for many years. In the 1970s, he said, “it was not uncommon to catch mink that had every phase of color there was. Jet black, pure white, some that looked like dairy cows.”
Hildebrandt said the harsh economics of fur farming mostly solved the escape issue. The price of a pelt, which always fluctuated with high fashion’s whims, has for the past few years not even covered the roughly $35 cost of raising the animal.
The industry in Wisconsin began with small family farms over a century ago, and those remaining are still all family farms, even if some are now owned by large foreign companies. But they are mostly large, with very secure fences. The fences exist to keep wildlife from helping themselves to the minks’ food or passing diseases to the captive mink. Whenever Hildebrandt makes his rounds to a ranch, he checks the guard fence.
Germ concerns heightened
Because mink live in such tight quarters and are so vulnerable to disease, ranchers were careful about germs long before COVID-19 struck, Hildebrandt said. Some already required workers to shower before and after shifts. It is also common to leave ranch clothes on the ranch, because mink are smelly.
Hildebrandt said mink operations are now limiting, as much as possible, how much they move or handle the animals. At some ranches everyone arriving is photographed, to assist with contact tracing. Workers and visitors are distanced and masked up, if not wearing the paper suits that health care workers don. “They wouldn’t last long with mink,” Hildebrandt said.
The CDC sent a field team to Wisconsin that ran through safety procedures for workers and ran a national webinar for mink ranchers. Government guidelines are all voluntary, except at the affected farms, which were quarantined.
At quarantined farms, anything coming in or out is controlled, including dead mink. Scientists are still assessing how much risk the bodies pose, Taylor said at the CDC’s December webinar on zoonotic disease updates. Hot composting can kill pathogens, but it has to be done right.
“After we went onto these farms and saw what they considered to be composting, which really were just piled-up mink, we made the decision here in Utah to just have these buried at landfills,” he said. To limit risk of the virus spreading further, the bodies must be buried immediately, predators and scavengers kept away, the lined trucks disinfected.
Currently, mink farmers are hanging onto this year’s pelts while scientists work out whether fur can spread the virus and if so how to decontaminate it. (Pelts currently on the market are all pre-pandemic, from last year’s mink.) So far the swabs haven’t turned up any virus, said Caitlin Cossaboom, a CDC veterinarian.
The question remains of how many farmed mink are out there, on the lam. Even in recent years, trapper Groehler has found a few mink with obvious “heavy ranch genetics,” which he suspects came from a few small, old-school ranches left in the area.
“A lot of people have a mindset that if the ranch mink would escape, it wouldn’t survive in the wild — they’re used to getting their food twice a day; they wouldn’t know how to hunt,” Groehler said. “But it’s interesting how things survive. They adapt. If you are hungry, you eat anything smaller than you.”
Mink better at pandemics than humans?
Groehler worries what the coronavirus might do among thousands of captive mink. “It can mutate from the mink, and what will it turn into next? What other animal species will it affect next? I don’t think anybody knows yet.”
The animals most at risk right now are the mink on farms. For mink, people are the disease reservoir. Though perhaps there is relief in sight. Three companies are presently working on mink vaccines that may be ready by the spring, Hildebrandt said. Some mink will be vaccinated before many of us are.
There are also reasons for hope in the nature of the virus and the mink. As infectious as it is, the virus doesn’t seem to stick around long outside its hosts — unlike, say, prions that cause chronic wasting disease; they can persist in soil for years.
The wild American mink, too, naturally follows CDC guidelines better than many of us have, preferring solitude to the company of its conspecifics.
As Groehler put it: “Wild mink socially distance very well.”