We recently read the news that Denmark has issued an order to cull all 17 million mink bred in the country. Let’s try to understand what happened.

On 5th November 2020, Danish health authorities reported 12 cases of COVID-19 due to a mink-specific variant of the coronavirus SARS-CoV-2. All 12 cases date back to September and are located in North Jutland (the northernmost region of Denmark, where Aalborg is located). Of these, 8 people had a connection to a mink farming industry and the remaining 4 cases were from the local community. This type of news is not new, as 214 human cases of COVID-19 have been recorded in Denmark since June 2020 due to variants of SARS-CoV-2 associated with farmed mink. The novelty concerning these 12 cases lies in the virus genome, which presents a combination of previously undocumented genetic mutations.

Where is the problem? The major concern is that this variant may be able to evade immunity guaranteed by vaccines currently under development. Most vaccines are designed against the Spike protein, which is the hook that allows the virus to anchor itself to the epithelial cells of the airways (the first step of infection). This means that if this protein were to mutate, the antibodies stimulated by the vaccine may not be able to recognize the new virus.

Denmark has determined that mink herds pose a significant risk to public health, due to mink’s susceptibility to SARS-CoV-2 infections and ease of animal-to-human transmission. Although thorough scientific and laboratory research is needed to assess these eventualities, Denmark does not want to take any chances and has ordered the culling of all farmed mink. The Scandinavian country immediately shared the genomic sequence of the new variant to help researchers study the effect of these mutations.

Animal-human transmission

Transmission of the virus from animals to humans is not surprising: Although COVID-19 spreads mainly from human to human, transmission between humans and some animals, such as minks, dogs, domestic cats and lions, has also been observed. Transmission from mink to humans has already been detected in Denmark, Spain, Sweden, Italy, the Netherlands and the United States of America. Minks are infected following exposure to infected humans. These animals can act as reservoirs of SARS-CoV-2, transmitting the virus between them and posing a risk of spreading the virus from mink to humans. A virus that moves from animals to humans is always a cause for concern, as species change could favor genetic mutations to promote adaptation to the new host.

The new viral variant

Based on the limited information available, the new variant does not appear to be associated with changes in infectivity or the severity of the associated disease. Indeed, early observations suggest that clinical presentation, severity and transmission among infected people are similar to those of other circulating SARS-CoV-2 viruses. The newly identified variant was called “cluster 5“, being the fifth identified associated with mink in Denmark. This variant has four simultaneous mutations affecting the Spike protein, which could allow it to evade vaccines under development against the traditional variant.

The implications of these mutations are not yet known, although preliminary studies suggest that this virus has a reduced susceptibility to antibodies developed against the original virus. By comparison, the mink virus belonging to cluster 1 does not show reduced susceptibility, while clusters 2-4 are still being analyzed.

Variability of virus SARS-CoV-2

Now you may be wondering “if there are 5 different variants of viruses infecting minks in Denmark, how many variants of SARS-CoV-2 are there in the world?” I realize that talking about mutations of the virus can generate perplexity about the validity of the vaccine, especially after what has been said about the risks in case of mutation of the Spike protein. However, most mutations have no bearing on vaccine efficacy because they do not translate into practice. This is why there are fewer strains than you might think. Below is an infographic of the various viral strains identified in Denmark; in red the cluster 5 associated with the mink is easily identifiable.

Each dot represents a viral genome sequenced between December 2019 and October 2020 in Denmark (3012 genomes). Each color represents a viral strain, classified according to the genetic sequence. Cluster 5, derived from strain 20B, is easily identified in red (top). Here is the original link of the graphic, which is interactive and edited by Emma Hodcroft and Richard Neher: https://nextstrain.org/groups/neherlab/ncov/denmark

It is important not to fall into error and to think that different strains have developed in each country: the strains widespread in the world are: 19A, 19B, 20A, 20B and 20C. Narrowing the focus to Europe, we can observe the presence of two further variants of the 20A strain, which are 20A.EU1 (originated in Spain) and 20A.EU2 (originated in France).

The Danish response

The Danish authorities have announced that they will take the following actions:

  • Culling of all farmed mink (15-17 million) in Denmark, including breeding stock;
  • Improve surveillance of the local population to detect all cases of COVID-19 in the North Jutland region;
  • Increased sequencing of human and mink SARS-CoV-2 infections (to keep viral genome mutations under control);
  • Rapid sharing of complete genomic sequences of the SARS-CoV-2 cluster 5 mink variant;
  • Introduction of new movement restrictions in affected areas in North Jutland to reduce disease transmission.