Denmark revealed in September that it would cull 17 million mink after a dozen people were infected with a mutated form of COVID-19 in North Jutland, eight from within the fur farming industry and a further four from within the communities nearby.
It wasn’t the first time that mink had contracted the virus and passed it on to humans. In April 2020, a mink farm worker in the Netherlands was diagnosed with COVID-19 and it was later proven that both human-to-mink and mink-to-human transmission can occur.
In the months since, infections in mink have been reported in Italy, Spain, Sweden and the United States.
The difference in Denmark was that the COVID-19 detected in the mink and the humans they infected was mutated, suggesting that even as pharmaceutical companies seem on the brink of a vaccine to the virus, new - and potentially more dangerous - strains may be evolving.
What is a mutation?
According to the European Centre for Disease Control (ECDC), COVID-19 has mutated at least 20 times since it was first detected in humans in 2019. Most of these mutations have had little effect on the virus and some have even made it weaker, according to a sample taken in October 2020.
But when a virus switches from one species to another, mutations can be more severe. The virus adapts and develops in a new host with different biological and genetic makeup. When it is then passed back to the original species, it may be a stronger and more resilient virus.
That means that if you have immunity to one strain of COVID-19 - through a vaccine, for example - but then contract another strain that has mutated in a different species, you may not have immunity.
What’s the good news?
Although the new strain had mutated, scientists don’t yet know whether that means that the virus is more deadly.
Indeed, the ECDC points out that while the strain is different, genetically, patients infected with mink-related variants have no worse symptoms to those with non-mink-related COVID-19. Equally, mink farming is a relatively small sector of the global agriculture industry and mink spreading COVID-19 across borders en masse is unlikely.
In its conclusions, the ECDC says that the overall risk to human health in the general population is low, while for those who work in mink-farming it is moderate.
Equally, while the outbreak in Denmark has been severe, in Italy in August a single mink was found to have contracted COVID-19 and although 1,500 of its fellow mink were tested, none were found to have contracted the virus.
Meanwhile, in the Netherlands, the outbreak led to the bringing forward of the ban on mink farming in the country from January 2021 to January 2024, which will be welcomed by animal rights groups.
And the bad news?
The mink variant has raised concerns because of its effect on antigenicity, which means the capacity to induce an immune response. Since vaccines are all about inducing immunity, the fear is that COVID-19 vaccines would not protect against this strain of the virus.
The worst-case scenario is that multiple new strains develop from animal-to-human and human-to-animal transmission, which could in theory require multiple vaccines. Given how long it takes to develop a vaccine, the fear is that COVID-19 keeps mutating and never goes away.
But - and it is a very big but - there is at present no evidence that this new strain is any less susceptible to the vaccines currently in development.
The most highly susceptible animals to SARS-CoV-2 are cats, lions, tigers, ferrets, mink and two species of hamster and bat, Egyptian fruit bat and Golden Syrian hamsters.
Mink come from the same family as ferrets, which as far back as the mid-1930s have been used by scientists to study influenza viruses and more recently to test flu vaccines and antivirals.
The reason ferrets make good subjects is because unlike mice - which are typically used as test subjects by scientists - they show symptoms similar to humans, including fever and sneezing.
But the reason COVID-19 spread so quickly among mink in Denmark is likely due to the intensive nature of the industry, which involves keeping hundreds of animals in steel mesh cages and in close quarters to each other.
Europe is the world leader in fur production, with more than 27 million mink pellets produced annually and more than 2,750 farms, 1,100 of them in Denmark.