SARS-CoV-2 strain variant associated with mink – Denmark

Since June 2020, Danish authorities have reported the widespread spread of SARS-CoV-2, a virus caused by COVID-19, on mink farms in Denmark. Danish public health authorities reported on 5 November
detection of a mink-associated variant of SARS-CoV-2 with a combination of mutations not previously observed (termed “Cluster 5”) in 12 human cases in North Jutland, detected from August to September 2020..

To date, the Statens Serum Institute (SSI) in Denmark has identified seven unique mutations in the SARS-CoV-2 class protein among variants circulating in kuna and humans. SSI bred a variant of “Cluster 5” with four amino acid changes in the spike protein, which was identified in mink and isolated from 12 human cases recorded in North Jutland. Preliminary findings have suggested that there is less ability of antibodies to neutralize strain Cluster 5, which requires further investigation.

Following public health measures implemented by the Danish authorities, the incidence of COVID-19 in North Jutland decreased from 100 per 100,000 inhabitants in the week beginning 16 November (week 47) to 60 per 100,000 inhabitants in the week beginning 2 November (week 45). Over the past weeks, the Danish authorities have conducted mass testing of 111,447 individuals in North Jutland using the reverse transcriptase polymerase chain reaction (RT-PCR) and plan to carry out genetic sequencing for all positive samples.

In November 2020, there were 349 cases among people associated with kuna farming, an increase from 200 cases in October 2020. As of June 2020, a total of 644 people associated with mink farming had tested positive. Furthermore, at least 338 cases have been reported among people working with mink malting, in six factories and two small plants, suggesting that there is an increased risk of COVID-19 infection in people involved in mink breeding, shooting and pelting. As of 1 December 2020, a total of 289 mink farms have been affected, accounting for approximately 20% of all mink farms in Denmark.

From the week beginning June 6, 2020 (week 24) to the week beginning November 16, 2020 (week 47), 10,386 positive COVID-19 samples from unique individuals underwent sequencing of the entire genome, making up 17 , 6% of all positive samples in the appropriate time period. Of these sequenced samples, 750 were virus variants associated with infected mink. In addition, at least two new variants of SARS-CoV-2 have recently been discovered in Southern Denmark that are not genetically related to the original strain of the variant associated with Danish mink.

In Northern Denmark, the proportion of strains of variants associated with the mink SARS-CoV-2 among all sequenced samples decreased from 60% and 51% at 41 and 42 weeks to 26% and 31% at 46 and 47 weeks, respectively; in central Denmark the share increased from ~ 3% in weeks 41 and 42 to over 30% in weeks 46 and 47; in Southern Denmark the share increased from 0% in weeks 41 and 42 to 11% and 21% in weeks 46 and 47, noting that there are differences in the frequency of order and practice between different regions. In areas without affected mink farms, cases of people infected with the variant associated with mink occurred sporadically. As of November 20, no new cases of cluster 5 strain in humans have been detected by genetic sequencing, and authorities have estimated that the cluster 5 variant no longer circulates in humans.

It was previously reported that mink was infected with SARS-CoV-2, including two attacks on large mink farms in the Netherlands in April 2020. In addition, the Netherlands reported human infections with mink-associated strains of SARS-CoV-2. no Cluster 5 strains. To date, eight countries, namely Denmark, Lithuania, the Netherlands, Spain, Sweden, Italy and Greece and the United States, have reported COVID-19 in farmed mink to the World Organization for Animal Health (OIE).

Public health response

On November 4, 2020, Denmark decided to remove all farmed minks in Denmark. This decision was made on the basis of information that it was not possible to prevent the spread of the infection from farm to farm or from animals to humans, and mink acts as a reservoir and contributes to the permanent transmission of the disease in Denmark. On 5 November, restrictions on movement were introduced in the affected areas of North Jutland. On 6 November, Denmark shared the full sequences of the SARS-CoV-2 genome obtained from humans with the Global Bird Influenza Information Exchange (GISAID) platform and 133 mink sequences on 18 November. On 19 November 2020, the restrictions in North Jutland were lifted due to the reduced incidence and absence of new cases of the Cluster 5 variant identified in the affected areas.

By 25 November, mink on all 289 farmed mink farms and farms within the allocated zone had been abolished. In addition, mink farming is banned in Denmark until 31 December 2021, including the import and export of live mink. Economic support packages have been established for those affected.

The Danish authorities continued to work with the WHO Working Group on the Evolution of the SARS-CoV-2 Virus and agreed to share the SARS-CoV-2 cluster variant 5 with the COVID-19 network of reference laboratories for further studies and testing.

WHO risk assessment

All viruses, including SARS-CoV-2, are expected to change over time. SARS-CoV-2 strains that infect mink and are then transmitted back to humans may have acquired unique mutations to adapt to the mink host. Advanced laboratory testing is needed to fully understand the impact of new versions of SARS-CoV-2 on viral properties such as transmissibility, clinical presentation, and efficacy of diagnostics, therapy, and vaccines. These studies are long, complex and are done in close collaboration with different research groups.

Although public health and social measures implemented by Denmark have led to positive developments, recent discoveries of other variants related to minks among human cases in mid-Jutland and the detection of around 200 human cases among workers are worrying.

WHO advice

This event highlights the important role that farmed chicken populations can play in the ongoing transmission of SARS-CoV-2 and the critical importance of robust monitoring, sampling and sequencing of these viruses using the One Health approach, especially around areas where such animal reservoirs have been identified. The global importance of Denmark’s preliminary findings is potentially significant and the WHO recognizes the importance of rapidly sharing epidemiological, virological and full genome sequence data with other countries and research teams, including through open source platforms such as GISAID.

The WHO advises the following measures:

• Carry out further virological tests to understand the specific mutations described by Denmark and to investigate any changes in virus transmission and pathogenicity;
• Countries, especially those engaged in the breeding of mink and other furs, to increase the order of SARS-CoV-2 from human and animal samples, where possible, and to share sequence data, including the discovery of the same mutations;
• Countries that will step up surveillance of COVID-19 at the animal-human interface where sensitive reservoirs for animals, including mink and other fur farms, have been identified;
• Countries need to strengthen biosecurity and biosecurity measures in agriculture around known reservoirs for animals, especially on mink farms, to limit the risk of zoonotic events associated with SARS-CoV-2. This includes infection prevention and control measures for animal workers, farm visitors and those involved in livestock or animal shooting;
• Remind communities and health professionals of the basic principles of how to reduce the risk of transmitting acute respiratory infections:
• Avoiding close contact with people suffering from acute respiratory infections;
• Frequent hand washing, especially after direct contact with sick people or their surroundings;
• Avoid unprotected contact with farms or wildlife;
• Practicing cough etiquette, such as maintaining distance, covering coughs and sneezing with wipes or disposable clothing, and washing hands if symptoms of an acute respiratory infection occur;
• Improving standard infection prevention and control practices in health facilities, especially in emergency hospital wards.

The WHO recommends the above health measures to all passengers. In case of symptoms indicating acute respiratory illness during or after the trip, travelers are advised to seek medical attention and share their travel history with their doctor. Health authorities should work with the travel, transport and tourism sectors to provide passengers with information on reducing the overall risk of acute respiratory infections through health clinics, travel agencies, carriers and entry points.

The WHO advises against the application of any travel or trade restrictions for Denmark based on the data currently available in connection with this event.

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