Between 15 and 17 million animals will be slaughtered in the coming days for health reasons. Mink, small carnivorous mammals bred for their fur, are in the sights of the Danish authorities. The latter announced, Wednesday, November 4, that they would proceed with the slaughter of all mink raised on their territory, the country being the world’s largest producer of mink fur. For good reason: five farms have been identified as having been contaminated by a mutated version of Sars-CoV-2, the virus causing the Covid-19 pandemic.
Mink farms « have been detected positive for Sars-CoV-2 in the Netherlands since the end of April 2020 then in Denmark in mid-June, in Spain at the beginning of July and in the United States in August », notes the animal health epidemiological surveillance platform ESA. « As a precautionary measure and in order to avoid any mutation of the Sars-CoV-2 virus, the Dutch, Danish and then Spanish authorities have decided to slaughter all mink from the farms concerned », she reports. Of tens of thousands of these animals were slaughtered in the Netherlands during the summer. Governments have promised compensation to breeders.
Why is Denmark worried about the role of mink in the epidemic?
The link between the contaminations of these animals and human contaminations worries the health authorities. In the 783 human cases of Covid-19 detected in recent days in the Jutland region, which concentrates the largest number of farms, the tracing made it possible to identify a mink farm as the origin of the contamination, explains the Danish authority for the control of infectious diseases. Twelve people infected with the mutated version of the virus observed in these animals have been identified. These human cases are no longer carriers of the mutated virus, however, reassure the health authorities.
If the main route of transmission of Sars-Cov-2 remains human-to-human, the trail of contamination between animals and humans continues to be studied. Scientific studies are underway to establish the epidemiological role that certain animals, especially captive wild animals (such as mink), can play in the spread of the virus..
According to the World Health Organization, « in a few cases, mink infected by humans transmitted the virus to other people » and therefore played a role as a vector of contamination. « These are the first reported cases of transmission from animals to humans », the institution told AFP. For Kåre Mølbak, the head of the Danish infectious disease control authority,« the worst-case scenario is to have a pandemic that leaves here, in Denmark ».
Is the virus carried by mink different from that carried by humans?
The coronavirus identified in minks by the Danish authorities differs slightly from Sars-Cov-2 observed in humans. At least some strains of Sars-Cov-2 studied and known. Like any virus, Sars-Cov-2 is subject to mutations, explained in August Samira Fafi-Kremer, head of the virology laboratory at Strasbourg university hospitals, at franceinfo. This « punctual change in its genome » does not necessarily result in a worsening of the effects of the virus or its transmissibility. « More than 13,000 of these changes can be observed today in the 100,000 Sars-CoV-2 sequenced to date », reported in September the site The Conversation (article in English).
Across high coverage #SARSCoV2 genomes isolated from mink @GISAID we pick up unique mutations including one in the #spike protein which has appeared at least five times in phylogenetically distant #mink lineages. pic.twitter.com/HzRBDhR8Jq
– Lucy van Dorp (@LucyvanDorp) November 4, 2020
The mutation of the virus observed in people who have been infected with mink has not resulted in more serious effects of Covid-19, assure the Danish authorities. But mutated virus « does not react as much to antibodies as the normal virus. Antibodies still have an effect, but not as effective « , asserted the Minister of Health, Magnus Heunicke. What worries the health authorities: « LThe virus mutated via mink may create the risk that the future vaccine [contre le Covid-19] does not work as it should « , according to Prime Minister Mette Frederiksen.
Why could the spread of this mutation in humans make a vaccine less effective?
According to the Minister of Health, « Research has shown that the mutations may affect current candidates for a Covid-19 vaccine. » The lower efficacy of human antibodies observed with the mutated virus is « a threat to the development of vaccines against the coronavirus « , he asserted. If the mutated version of Sars-CoV-2 reacts less well to antibodies and spreads in the human population, this could pose a danger to the development of a vaccine against Covid-19. Because researchers are currently working on its development from known strains of Sars-Cov-2 and antibodies that can neutralize it.
This eventual « menace » is exaggerated, believes however François Balloux, professor at University College London and specialist in pathogen evolution. « There are thousands of Sars-Cov-2 mutations that are constantly appearing. The fact that a few have been seen in mink will not change the strains circulating in humans. If they favored transmission of the virus to the man, [ces souches] would already have a high frequency « , he wrote on Twitter.
The ‘vaccine escape’ scare story is just idiotic. Vaccine-escape mutations may (or not) arise in humans in the future, if they are advantageous to the virus for (once vaccines will be deployed). They definitely won’t be fuelled by mutations having emerged in minks.
— Prof Francois Balloux (@BallouxFrancois) November 4, 2020
Furthermore, the danger that these mutations may represent for the future vaccine is not yet known. Some viruses such as influenza mutate considerably from year to year and thus bypass the effectiveness of vaccines. But others, like measles, change over time without compromising the effectiveness of the vaccine.
Are other animals likely to spread mutations in humans?
« Animals play a minor role in the pandemic, but it is important to study them because they could potentially be a reservoir for the virus, » says Arjan Stegeman, farm animal health specialist at Utrecht University (Netherlands) in an interview (article in English). This professor co-carried out a study on cases of Sars-Cov-2 contamination in Dutch mink farms in April and May 2020. The fact that this carnivorous mammal is particularly sensitive to Sars-CoV-2 did not really surprise him because « mink can contract most respiratory infections that affect humans, and therefore also transmit them « , he explains. In addition, the breeding conditions favor the circulation of viruses because of the proximity of the animals or the lack of ventilation.
Sars-CoV-2 can infect other animals, including cats, dogs, tigers, hamsters, or macaques. Studies are continuing to assess the risks of other types of farming, especially domestic animals. « AT To date, the results of experimental infection studies suggest that poultry and pigs are not susceptible to infection by Sars-CoV-2 « , specifies the World Organization for Animal Health. Likewise, there does not existThere is currently no evidence that pets play an epidemiological role in the spread of the coronavirus, reassures the animal epidemiological surveillance platform.