COVID-19 detected on multiple Dutch mink farms

October 25, 2020

Mink have tested positive with COVID-19 at 69 mink farms in the Netherlands. The mink showed various symptoms including respiratory problems. It seems the animals got infected by employees.
Research since has shown that mink have transmitted the virus to each other. It is also plausible that employees have been infected by mink. A mandatory screening of all Dutch mink farms has been instituted and infected mink farms are culled as of 5 June. A manditory closing scheme for Dutch mink farms will be introduced early on in 2021.

The Animal Health Service (GD), Utrecht University (UU), Erasmus MC (EMC) and Wageningen Bioveterinary Research (WBVR) are conducting research to gain more insight into the virus, the spread of the virus and the spread in the environment. Samples of sick and healthy animals have been collected and air and dust samples have also been taken in the vicinity of the farms. GGD is involved in sampling and research into contamination of employees.

Closing scheme for Dutch mink farms

At the request of the government the Outbreak Management Team Zoönosen (OMT-Z), in which Wageningen Bioveterinary Research also has a seat, has reviewed the situation at mink farms. The OMT-Z states that, despite the limited risk to public health at the moment, it is desirable to stop the spread of the virus within mink farms. On the basis of the investigations that have been carried out, the cabinet has decided to introduce a mandatory closing scheme for all mink farms in the Netherlands. Infected farms are culled and an even stricter control will be instituted on all other mink farms, so that any new infections can be to be discovered. Strict precautions apply to all mink farms to prevent the spread of the virus. This is stated in a letter to Parliament dated 28 August.

Legislation is being prepared to close all mink farms early on in 2021. This is stated in a letter to Parliament dated 11 November.

Culling of contaminated mink farms from 5 June

The Dutch government announced that the mink farms infected with COVID-19 are culled from Friday 5 June. It concerns 68 infected farms. The government took this decision on the basis of the advice of the Outbreak Management Team for Zoonoses (OMT-Z) and the Administrative Coordination Consultation for Zoonoses. The advice to cull was given because the virus can continue to circulate on mink farms for a long time and can therefore pose a risk to public and animal health.

Risk analysis 20 July

In a letter to parliament dated 20 July, the OMT-Z recommends expanding existing measures for persons who are in contact with mink. If new infections are still being detected on Dutch mink farms after mid-August, it is advised to cull all mink farms to prevent them from becoming a reservoir for the coronavirus.

Spread of the virus between mink

Previous research has shown that ferrets are susceptible to SARS-CoV2. Therefore it was already assumed that mink might be susceptible too. Pneumonia was seen in sections on mink and SARS-CoV-2 was detected in organs and throat swabs. Based on the variations in the genetic codes of the virus, it could be concluded that mink farms have transmitted the virus to each other.

Spread from mink to employees likely

Minister Schouten of Agriculture, Nature and Food Quality (LNV) reports in letters to parliament dated 19 and 25 May that it is plausible that employees were infected with the coronavirus by mink.

Further investigation of the increasing number of infected mink farms has shown that many of the employees surveyed were infected with coronavirus (more than 50 percent). Building blocks of the virus determined that this virus was similar to the virus that was circulating in the mink on the farm. On this basis, it can be concluded that many of these people are very likely to be directly or indirectly infected by the mink.

Announced measures for mink farms

All Dutch mink farms will be screened and visitors are banned from visiting the stables. A reporting obligation has been introduced and employees are required to wear protective clothing. A ban has also been imposed on the transport of mink. Manure from infected mink farms may only be transported to biogas plants where it is heated to at least 70˚C. The existing hygiene protocol is sharpened, with special attention being paid to the testing of employees.

First results screening

During the compulsory screening that is being carried out among all Dutch mink farms since 25 May, COVID0-19 infected mink were found at multiple farms. This is stated in letters to Parliament by the Minister.

Rapid detection of new infections

Wageningen Bioveterinary Research is involved in the early warning programme (weekly submission of naturally dead animals). This programme may enable new suspected and infected farms to be found in the coming period. The ELISA test (serological), which is used for the screening of all Dutch mink farms, is now ready for use. Blood samples from farms that are tested positive in the ELISA test are sent to WBVR for confirmation.

Virus in dust particles in the stables

Virus RNA has been detected in dust particles in the stables, which indicates that people in the stables with infected minks can be exposed to coronavirus.

No virus found in outside air samples

The first results show that no virus was found in the air samples outside the farms. However, virus has been found in the immediate vicinity of mink on dust particles within the farms. It is not unknown if people can become infected with COVID-19 through these dust particles. Minister Schouten reported this in a letter to parliament dated 8 May. The National Institute for Public Health and the Environment (RIVM) indicates that the risk of exposure of people to the virus outside the farms is negligible.

Precautionary measures in the area withdrawn

In the second sampling series, the virus was no longer found in dust particles in the air inside or outside the farms. The previous advice not to walk or cycle in a 400 meter radius around an infected mink farm has therefore been withdrawn by Minister Schouten on 15 May.

Cats and dogs at the infected mink farms

During the investigation at the mink farms, cats and dogs from the infected farm locations were tested for infections with the coronavirus.

  • Only the first six farms showed infections in cats based on virus detection or detection of antibodies against COVID-19, which means that the cats have been infected.
  • At least eleven dogs have been tested for COVID-19 contamination, but no COVID-19 contamination was found in any of these dogs. Dogs can therefore be excluded as carriers of the virus.

It does not seem very likely that cats play a role in spreading the coronavirus. But given the many households with a cat in the Netherlands, it is important to further investigate the role of cats in the potential virus transmission of this respiratory tract infection. In this context, research into - among other things - (virus) transmission in cats is carried out by a partnership with research groups united in the Netherlands Center for One Health (Faculty of Veterinary Medicine of Utrecht University, Wageningen University & Research, Erasmus MC Rotterdam and research centers in human health care).

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