That means a high density of animals, for sure, and as always one of the big challenges under such conditions is control of disease. In my own homeland of Arkansas, the rise of large-scale catfish farming was partly a story of figuring out what the optimum fish density was that didn’t lead to finding them all floating on the surface of the pond one morning. American mink farms are already known to be a reservoir for Aleutian disease. The parvovirus responsible for that one has been mutating under the selection pressure of intense farming, and you would expect this to be the case with other infectious agents as well.
Like the current coronavirus. Back in the spring and early summer, mink farmers in the Netherlands reported coronavirus outbreaks in their animals, and this was followed by reports from Denmark and other countries in Europe. Utah fur ranches reported coronavirus outbreaks in their mink populations (with thousands of dead animals) in August. On both continents, it’s believed that the disease spread from the human farm workers into the mink populations. Different mammals have different susceptibilities to the virus (to any virus), and it appears that Covid-19 is highly transmissible in mink. Its mortality rate is not high, fortunately, but high enough given the huge numbers of animal involved. For “herd immunity” fans, the outbreaks seem to tail off once about 90% of the population has been exposed, but that’s a lot higher number than you’d ever want to hit, and it’s also worth noting that the human population is not well modeled by the conditions on a mink farm. Yet.
The coronavirus has spread and mutated in the Danish mink population, and now there have been cases of these strains jumping back into humans and causing infections there. This was first seen in a single case in the Netherlands in the spring (more here), and it’s happened a number of times since. It gets worse: reports have it that some of the current mink strains in Denmark are less susceptible to antibody responses.
Now, I am not completely sure what that means. I have been trying to find published details, but it seems to be too early, and the press reports are full of other baffled scientists waiting for information. The Serum Science Institute in Denmark seems to be the place where these effects were found, and they’ve shared their findings with the WHO and the European Centre for Disease Prevention and Control. But the actual results don’t seem to have been released yet. But if I’m translating this correctly, Kåre Mølbak of that institute said at a press conference that the situation is “very serious” and that the worst case would be a restarted pandemic spreading out of Denmark. The article also says, rather alarmingly, that “The Serum Institute estimates that five percent of the viral infections among people in North Jutland are of the new type of virus mutation“, and I would very much like to hear some more about that.
But you can see that the Danish government is taking this seriously: all 17 million mink in the country are being killed off immediately in a gigantic cull. The police, the armed forces, and the Home Guard are all involved, and apparently they’re throwing everything they have at the effort. The Netherlands has already sped up an existing proposal to ban mink farming, which is now set to take place by the end of this year, and you can bet that they’re looking at the Danish results very closely. But the places to watch are Poland and China: these are big mink pelt producers, and (as far as I can see) nothing has been heard from them about this new problem.
I assume that we’ll be seeing sequence information very shortly, as well as the details of the antibody studies. I’ll dive right into those details as soon as they’re available, believe me!
