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January 01, 2021

Denmark culling minks in attempt to eliminate SARS-CoV-2 variant

Spike protein mutation could affect antibody response
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Government authorities and mink breeders in Denmark have depopulated millions of minks partly in an attempt to contain a SARS-CoV-2 variant seen as a danger to humans.

That variant contains mutations that Danish officials said could make it less susceptible to antibodies against other SARS-CoV-2 strains. The country had already depopulated minks on hundreds of farms with SARS-CoV-2 infections before discovery of the variant.

All SARS-CoV-2–infected minks and minks in risk zones have been depopulated, according to a Nov. 27, 2020, press release from the Danish Veterinary and Food Administration. The mink population previously totaled an estimated 15 million.

The administration, national police, Danish Emergency Management Agency, and armed forces worked with mink breeders to depopulate and dispose of approximately 11 million minks on 288 properties with infected minks and 446 properties in the risk zones. In addition, most mink breeders outside the risk zones stated they have depopulated their minks.

“However, the Danish Veterinary and Food Administration does not expect all mink to be killed before the new law banning the keeping of mink enters into force,” stated the release, as translated from Danish. Therefore, new infected herds may continue to be detected through ongoing surveillance.

A working paper from the Danish government indicates the SARS-CoV-2 variant of most concern has changes to its spike surface glycoprotein that could make it less recognizable to antibodies created in response to infection with or vaccination against another SARS-CoV-2 strain. A Cornell University researcher with expertise on coronaviruses said the effect appears to be modest, and the variant is worth attention but not panic.

A Nov. 12, 2020, rapid risk assessment by the European Centre for Disease Prevention and Control stated that, of the mink-related variants analyzed, only one raised specific concern because of its effect on antigenicity. Further investigations were needed to assess whether the variant would have any impact on risk of reinfection in humans, reduce vaccine efficacy, or reduce the benefit of treatment with plasma from convalescent patients or monoclonal antibodies.

“It should be noted that continued transmission of SARS-CoV-2 in mink farms may eventually give rise to other variants of concern,” according to the assessment.

Maps (U.S. and Europe): SARS-CoV-2 infections in farmed minks
According to the World Organisation for Animal Health (OIE), as of Nov. 30, 2020, Denmark, France, Greece, Italy, Lithuania, the Netherlands, Spain, Sweden, and, in the U.S., Michigan, Oregon, Utah, and Wisconsin had reported SARS-CoV-2 in farmed minks.

Infections spread between minks, humans

According to the World Organisation for Animal Health (OIE), as of Nov. 30, 2020, Denmark, France, Greece, Italy, Lithuania, the Netherlands, Spain, Sweden, and, in the U.S., Michigan, Oregon, Utah, and Wisconsin had reported SARS-CoV-2 infections in farmed minks.

A Nov. 6, 2020, World Health Organization report states that, since June, 214 people in Denmark had been infected with SARS-CoV-2 variants associated with farmed minks, and 12 of them were infected with a unique variant with previously unseen mutations. Initial observations suggested similarities to other SARS-CoV-2 infections in terms of clinical presentation, disease severity, and virus transmission.

“Preliminary findings indicate that this particular mink-associated variant identified in both minks and the 12 human cases has moderately decreased sensitivity to neutralizing antibodies,” the announcement states. “Further scientific and laboratory-based studies are required to verify preliminary findings reported and to understand any potential implications of this finding in terms of diagnostics, therapeutics and vaccines in development.

“In the meantime, actions are being taken by Danish authorities to limit the further spread of this variant of the virus among mink and human populations.”

The 12 people infected with the variant were ages 7-79 years, and eight had links to the mink farming industry. Four were from a local community near a farm.

All of those infections occurred in the North Jutland region, where national authorities increased restrictions on gatherings, limited visits from people who are not permanent residents in Denmark, and encouraged all citizens to get tested for SARS-CoV-2. That included encouragement for people to get tested every three or four days if they have connections to mink farming.

Antibody effects may be mild

Gary R. Whittaker, PhD, who is a professor of virology at the Cornell University College of Veterinary Medicine, studies the structures and genetic functions of coronaviruses. He is helping lead a group of laboratories studying SARS-CoV-2. He also co-authored a scientific article on coronavirus susceptibility and transmission among minks and other mustelids; that article was pending publication in mBio at press time.

He said coronaviruses mutate often, especially in the spike protein they use to bind with a host cell’s receptors. Those mutations should be taken seriously and studied, but he expressed skepticism that the variant that inspired the cull order in Denmark could evade immune responses well enough to scuttle vaccination plans.

“It’s not impossible, but there’s not really very good evidence,” he said.

The variant targeted by Danish authorities seemed to have a mutation with modest effects on one component of the immune response, Dr. Whittaker said. But any vaccines that gain approval probably will induce an immune response with broad enough effects to protect people.

He noted that the changes so far appear to be results of conventional variations, rather than recombination with other coronaviruses circulating in animals. Such variations are possible as the virus spreads and evolves, and mink farms may accelerate that change, Dr. Whittaker said.

“The virus is going to be sampling different genetic space and just figuring out what’s best for the virus, in a way,” he said. “I think the concentration of animals, it just allows that selection to be fast forwarded.”

Managing the risk from such variants is a complex problem that may have no simple answers, Dr. Whittaker said, although he called the decision to euthanize all of Denmark’s minks a draconian response that raises concerns about the welfare of the animals and safety of people conducting the depopulation. But he noted that the world continues struggling, in general, in responding to COVID-19.

The WHO report notes that advanced laboratory studies are needed to show the impact of specific mutations.

The findings of the Danish public health authority, Statens Serum Institut, need verification, according to the WHO. Further studies could give information on the mutations and their effects on transmission, clinical presentation, diagnostics, therapeutics, and vaccines. WHO officials plan to work with Danish officials on those studies and analyses.


The OIE and AVMA provide information on SARS-CoV-2 in animals.