Can COVID-19 be transmitted between humans and animals?

Since June 2020, SARS-CoV-2 variants associated with farmed minks have been found in Denmark in 214 human cases of COVID-19, including 12 cases with a specific variant, published on 5 November.

All 12 cases were found in North Jutland, Denmark, in September 2020. The cases ranged from 7 to 79 years of age, and eight had a relation with the mink farming industry and four cases were from the local community.

Initial findings indicate that the clinical appearance, severity and transmission of SARS-CoV-2 viruses among those infected is comparable to that of other circulating SARS-CoV-2 viruses.

However, this version, referred to as the variant of cluster 5, had a combination of mutations or modifications that had not been observed previously.

The consequences of the described modifications in this version are not yet well known. Preliminary results suggest that this unique mink-associated variant has moderately decreased sensitivity to neutralising antibodies found in both minks and the 12 human cases.

Further scientific and laboratory-based studies are necessary to validate the documented preliminary findings and to understand any possible diagnostic, therapeutic and developmental vaccine implications of this result.

Meanwhile, the Danish authorities are taking measures to restrict the further spread of this form of the virus among the mink and human populations.

In December 2019, SARS-CoV-2, the virus that induces COVID-19, was first described in humans. As of November 6, more than 48 million people have been affected, causing over 1.2 million deaths worldwide.

While it is suspected that the virus is ancestrally related to bats, the origin of the virus and the SARS-CoV-2 intermediate host(s) have not yet been determined.

Available evidence suggests that the virus is primarily transmitted through respiratory droplets and near contact between humans, but there are also examples of human-animal transmission.

Several species, such as minks, rats, domestic cats, lions and tigers, that have been in contact with infected humans, have tested positive for SARS-CoV-2.

Following contact from infected humans, minks became infected. Minks may serve as a SARS-CoV-2 reservoir, transferring the virus between them, and posing a risk of mink-to-human spill-over of the virus.

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Within the human population, individuals will then spread this virus. In addition, spill-back (transmission of human to mink) may occur. When any animal virus spills into the human population, or when an animal population may contribute to amplifying and transmitting a human-affecting virus, it remains a concern. Genetic changes in the virus can occur when viruses pass between human and animal populations.

Via whole genome sequencing, these variations can be detected, and when discovered, studies can study the potential effects of these changes on the disease in humans.

To date, six countries have recorded SARS-CoV-2 in farmed minks to the World Animal Health Organization, namely Denmark, the Netherlands, Spain, Sweden, Italy and the United States of America (OIE).

Responsive to public health
The following planned or ongoing public health measures were declared by the Danish authorities:

Culling in Denmark, including its breeding stock, of all farmed minks (more than 17 million);
Improving local population surveillance to detect all cases of COVID-19, including via population-wide mass PCR testing for the North Jutland region;
Expanding the proportion of human and mink sequencing of SARS-CoV-2 infections in Denmark;
Rapid exchange of mink-variant SARS-CoV-2 complete genome sequences; and
Introduction of new restrictions on movement and other public health initiatives to affected areas in North Jutland in order to limit further transmission, including restrictions on movement between municipalities.
Risk assessment by WHO
All viruses, SARS-CoV-2 included, alter over time. Special combinations of mutations may have been acquired by SARS-CoV-2 strains infecting minks that are subsequently transmitted to humans. Advanced laboratory studies are needed in order to fully understand the effect of particular mutations. These studies take time and are carried out between various study groups in close collaboration.

Recent results published in Denmark by the Danish Public Health Authority (Statens Serum Institut) concerning the novel form of SARS-CoV-2 found in humans need to be verified and further assessed in order to better understand any possible transmission, clinical appearance, diagnostics, therapeutics and vaccine production implications.

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In addition, to better understand the identified mutations, comprehensive observations and scientific studies are required. Detailed studies by collaborators will continue to promote the exchange of complete genome sequences of human and animal strains.

Working with Danish scientists, members of the WHO SARS-CoV-2 Virus Evolution Working Group are working to better understand the outcomes available and collaborate on further studies. In order to understand the effects of these viruses in terms of available SARS-CoV-2 diagnostics, therapeutics and vaccines in progress, further scientific and laboratory-based studies will be carried out.

Actions taken by the Danish authorities would restrict the continued spread of SARS-CoV-2 mink-associated variants in Denmark and have been introduced, in particular, to contain the specific variant identified to the WHO.

These steps include the restriction of human travel, the killing of animals, systematic testing of people living in affected areas, and increased national genomic sequencing of SARS-CoV-2 viruses.

Advising the WHO
This event highlights the important role that farmed mink populations can play in the ongoing transmission of SARS-CoV-2 and the critical role of strong SARS-CoV-2 surveillance, sampling and sequencing, especially in areas where such reservoirs of animals are identified.

Denmark’s preliminary results are important worldwide and WHO recognises the value of exchanging information on the epidemiological, virological and complete genome sequence with other countries and research teams, including through open source platforms.

In order to understand the particular mutations identified by Denmark and to further examine any epidemiological changes in the function of the virus in terms of its transmissibility and the seriousness of the disease it causes, further virological studies should be performed by the WHO.

The WHO advises all countries to increase, where possible, the sequencing of SARS-CoV-2 viruses and international sharing of sequence data.

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WHO is urging all countries to improve COVID-19 surveillance at the animal-human interface where susceptible animal reservoirs, including mink farms, are identified.

In order to minimise the risk of zoonotic events associated with SARS-CoV-2, the WHO also reminds countries to improve agricultural biosafety and biosafety measures around established animal reservoirs.

This involves steps for livestock workers, farm tourists and others who may be interested in animal husbandry or culling to avoid and manage infections.

The basic principles for reducing the general risk of acute respiratory infections being transmitted are as follows:

The avoidance of direct contact with persons with acute respiratory infections;
Ensuring regular hand-washing, especially after direct contact with or in the environment of ill people;
Practicing cough etiquette, such as maintaining distance, covering coughs and sneezes with disposable tissues or clothes, and washing hands for people with symptoms of acute respiratory infection; using masks where appropriate; and
Improving traditional infection prevention and control practises in health care facilities in hospitals, especially in emergency departments.
The WHO shall advise against the application to Denmark of any travel or trade restrictions on the basis of the currently available information on this case. Since resuming international travel, the WHO has provided guidance on public health considerations, recommending a comprehensive risk assessment, taking into account the context of the region, local epidemiology and transmission trends, national health and social outbreak management steps, and the ability of health systems in both departure and destination countries, including entry points. Travelers are advised to seek medical attention and share their travel history with their health care provider in case of symptoms that indicate acute respiratory disease either during or after travel. In order to minimise the general risk of acute respiratory infections, health authorities can collaborate with the travel, transport and tourism sectors to provide travellers with information through travel health clinics, travel agencies, transportation operators and points of entry.