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Why do the Danes kill minks

Vera Mukhina, N+1

At the beginning of this month, the Danish authorities began to destroy minks – and there are about 17 million of them in Denmark, more than three times more than the Danes themselves. There are so many minks in the country that the military had to be sent to help the farmers. While the animals were being killed, the government found out that the order given was illegal, and instead of "carpet" destruction of minks switched to "spot". Let's figure out what's wrong in the Danish Kingdom and, it seems, threatens to continue in Ireland and Sweden.

COVID-19 is an example of a typical zoonotic infection. Who exactly transmitted this disease to people is still unknown, but everything points to wild animals – most likely bats. Perhaps some other intermediate species was involved, as in the case of SARS in 2009. Then civets, an intermediate link between bats and humans, played an important role. Living in them, the virus accumulated mutations that allowed it to jump over to a human.

With SARS-CoV-2, it quickly became clear that cases of reverse zoonosis are also possible, when animals living next to humans are susceptible to the virus. Laboratory testing showed that animals with a similar structure of the ACE2 receptor – macaques, ferrets and cats – turned out to be suitable carriers and were able to transmit the virus to each other, and animals with dissimilar ACE2 (for example, dogs, pigs and poultry), if they get sick, are extremely reluctant.

This was quickly confirmed: there were reports of infection of domestic cats of patients with COVID-19, and lions and tigers began to get sick in zoos. However, no additional restrictions were imposed in connection with this discovery. WHO recommended distancing yourself from pets during the illness and that's it. There have been no cases of human infection from a cat yet.

There are no such rich field statistics for ferrets – they are not very common as a pet, and there are not so many contacts with humans in wild animals. But minks and other martens related to ferrets are actively bred on fur farms – therefore it is not so surprising that the first signals of infection with SARS-CoV-2 came from there.

The main reasons for the current concern are outlined in the report The State Serum Institute of Denmark (Statens Serum Institut, SSI) and an article by Dutch scientists led by Bas B. Oude Munnink, published recently in the journal Science.

Burrowing virus in the Netherlands

The Dutch analyzed the diagnoses and genetic sequences of viruses that circulated among minks (n=88) and humans (n=18) on 16 farms and found that:

• minks were infected by farm workers;
• the virus is perfectly transmitted from mink to mink;
• due to the rapid rotation on animal farms, mutations accumulate in viruses;
• the virus can be transmitted back from minks to people – it became clear from the fact that in the samples of sick farm workers there were viruses with mutations characteristic of minks;
• judging by the symptoms, the burrowing version of the virus is no more dangerous for people than SARS-CoV-2.

Judging by this article, minks are no more dangerous for people than other people in the conditions of the COVID-19 pandemic – they can also be infected, they can also be infected from them.

But their crowding and good susceptibility gives the virus the opportunity to multiply uncontrollably on farms and evolve quickly – because minks do not wear masks and do not observe social distancing. From the point of view of epidemiology, this is not very good – the chances of the appearance of some particularly contagious or aggressive variant of the virus, naturally, increase.

There have been no vivid examples of some animal population first becoming infected from humans, and then returning them a "weighted" version of the virus, but this is what scientists fear. Farms can become very effective "natural laboratories" for the disease: the crowding of animals creates conditions for the virus to multiply in the population, and regular contact with people allows the pathogen to "check" new mutations on them.

Burrowing virus in Denmark

Since the beginning of June in Denmark has infected minks on 191 farms. In the regions where they are located, the number of COVID-19 cases has increased in recent months. It is estimated that about half of the new cases of SARS-CoV-2 infection in Northern Jutland – the region where the main animal farms are concentrated – may be directly or indirectly related to mink farms. This is an approximation: during the pandemic, scientists sequenced viruses in randomly selected patients (14.9 percent of the total number of cases in the region), and it determined the proportion of those who fell ill with a variant in which there were mink mutations. It turned out that from September to October, it increased from 18 to 53 percent. But the representativeness of the sample is, of course, vulnerable to criticism.

170 variants of the virus are circulating in mink populations on 40 farms studied by researchers. Of these, only five options were passed on to people. There is not a single one among them that would be more contagious or cause a more serious illness than the "classic" COVID-19.

But two of them attracted the attention of scientists.

1) A variant of the "fifth cluster". It was found in minks on five farms and in 12 people, among whom only four were directly connected with farms. In this variant, there are five mutations, three substitutions and two deletions. Scientists have not yet specified exactly where they are located in the genome of the virus.

The researchers conducted an experiment in which they tried to neutralize this virus with antibodies from people who had been ill with the usual SARS-CoV-2 – and failed. This may mean that vaccines "trained" to recognize SARS-CoV-2 may have problems with the mink variant of the virus. In addition, those who have already been ill with COVID-19 may be defenseless against the virus released from mink farms.

These data, however, are preliminary – and they definitely require further confirmation and study. So far, they do not allow us to draw any conclusions about vaccines or therapy – there is too little data. So far, it is impossible to consider this option more (or less) dangerous than the others.

In addition, according to Oxford virologist Astrid Iversen, who participated in the experiment, this variant has not spread widely – it has not been seen in the testing data since September.

2) A variant with the Y453F mutation in the S-protein gene. This is another variant of the mink coronavirus, which Danish researchers plan to monitor especially closely.

Unlike the "fifth cluster", it has spread more widely: it was found in three hundred people in Denmark and the Netherlands. In addition, judging by the database data gisaid.org , the same mutation was found in isolated cases in the Faroe Islands, Switzerland, South Africa and Of Russia. Whether all these cases are related to each other is not yet clear.

The Danish version of this virus in several cases could not detect commercial "express tests" based on monoclonal antibodies. But the accuracy of these tests is on average lower than that of PCR tests, so false negative test results may be associated not with a mutation, but with a banal imperfection of the test. In addition, all this does not mean that the Y453F mutation can reduce the effectiveness of vaccines: antibodies to the virus as a result of vaccination are developed individually in the human body, and unlike the commercial standard, they can quite successfully recognize the mutant antigen.

What is the result?

• Minks can really be infected with coronavirus.
• You can get COVID-19 from minks.
• Mink farms are an effective incubator for accelerated virus evolution. There are a lot of minks on farms, they infect each other, and therefore the virus accumulates mutations faster in their populations.
• At the moment, any particular danger of those options that have already been found on farms in the Netherlands and Denmark has not yet been proven.

The struggle with nature

The absence of a "super virus" is not a reason to relax, because at any moment the situation can change. To become a "super-", a pathogen sometimes needs only a few successful mutations.

For a long time, avian flu was transmitted only between birds. At the beginning of the two thousandth there were cases of transmission of the virus from poultry to humans. A person tolerates bird flu very hard, and now bird flu is treated especially carefully. The transmission of avian flu from person to person was – fortunately – impossible. But in 2012, scientists created a variant of the avian flu virus that could be transmitted by air between ferrets. The work – after numerous prohibitions and debates – was published, but soon a law was passed that almost completely prohibits such experiments. But the main thing that we learned from this work is that it takes only a few mutations for the virus to move to spread between mammals. And, therefore, the risk of such a strain appearing in nature is great.

It is difficult to prevent the virus from mutating and adapting to the environment further – you can only slow it down. The main methods of combating "undesirable" evolution and the transfer of dangerous diseases are rather clumsy: to destroy potentially dangerous animals and limit their contact with humans. This is what they do now in all cases when avian flu is detected in poultry farms: birds are simply destroyed. Right now, there is an outbreak of avian flu in Denmark, Japan and some other countries, and farmers will have to slaughter almost a million birds. And during the epidemic of the first SARS in In China, it was decided to destroy all palm civets on farms – simply because this species turned out to be a carrier of SARS-1. So the reaction of the Danes in this regard does not look unprecedented – although there have never been such large-scale killings of farm animals under the banner of epidemiological safety of people.

The alternative to murder would be vaccination, treatment or isolation, but this is not possible in all cases. So, they are trying to vaccinate birds against influenza, but now even people do not yet have either a vaccine for SARS-CoV-2 or a cure for COVID-19.

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