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SARS-CoV2 infection in farmed mink, Netherlands, April 2020

Our take —

In this study available as a preprint and thus not yet peer reviewed, farmed mink at two locations in the Netherlands became infected with SARS-CoV-2, and developed respiratory symptoms following suspected exposure to farm workers with COVID-19 at each farm. The presence of viral RNA in inhalable dust from the mink housing areas suggests airborne transmission between minks, and may pose a risk for mink-to-human transmission. The Dutch government has now reported two cases of COVID-19 in farm workers that are likely due to mink-to-human transmission, and will cull animals on infected mink farms in the country.

Study design

Ecological

Study population and setting

Signs of respiratory disease and mortality were reported in minks on two farms (NB1 and NB2) in Noord Brabant province, Netherlands on April 19 to 20, 2020. Suspecting infection with SARS-CoV-2, researchers collected samples from lungs of three deceased animals from each farm on April 21 and 25, 2020. Samples from animals on each farm each farm (one index animal and four additional animals from NB1; one index animal and five additional animals from NB2) were collected to sequence genetic material of the virus. In the following week, 36 deceased animals (18 per farm) were collected and necropsied, and individual throat and rectal swabs were collected for detection of the viral genetic material. Inhalable dust inside of mink houses on farms was also sampled between April 28 and May 2, 2020 via air pumps for 5-6 hours to test for viral genetic material.

Summary of Main Findings

At the time of reporting, the sick minks showed signs of watery nasal discharge, with severe respiratory distress in some animals; necropsied animals showed signs of pneumonia in lungs tissues (16/18 from NB1 and 12/18 from NB2). Mortality in animals on the farms was 2-4 times higher in the period from April 19 to 30, 2020 than background mortality from past data. SARS-CoV-2 RNA was found in all seven mink from which organs were collected, in the nasal conchae, lung, throat swabs, and rectal swabs, with a total of 36/36 positive throat swabs and 34/36 positive rectal swabs.

One farm worker on farm NB1 had shown symptoms consistent with COVID-19 at the beginning of April, 2020 but was not tested for SARS-CoV-2. A farm worker at NB2 was diagnosed with COVID-19 and hospitalized on March 31, 2020 but could not produce a sufficient viral load for sequencing. The viral genomes from positive minks on each farm were similar to other sequences from human cases from within the Netherlands, but the viral sequences from animals from the two farms clustered into separate genetic groups by farm, suggesting independent exposure events on each farm from infected workers. Additionally, viral RNA was detected in 3/6 inhalable dust samples from NB1 and 1/3 from NB2.

Study Strengths

The sequencing of viral RNA from animals on each farm clarifies the separate origins of infection on the farms. Sequencing of viral RNA in inhalable dust provides some evidence that transmission of the virus between animals is through an airborne route.

Limitations

The authors can only suspect that the mink infections on each farm were seeded by the sick farm workers due to the lack of genetic sequences from the human cases. It is also unclear from the limited sampling what the overall incidence of infection was on each farm. Additional testing of animals would be needed to assess the number of animals that were infected, but showed no clinical signs or mortality, and if mink develop antibodies to SARS-CoV-2 following infection.

Value added

This study broadens the number of domesticated and farmed animals that are susceptible to SARS-CoV-2 following exposure to human COVID-19 cases.

This review was posted on: 17 June 2020