Epidemiological study – Mink Netherlands

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Mink Netherlands

Published 9 November 2020

Munnink, B.B.O. et al. (2020) Jumping back and forth: anthropozoonotic and zoonotic transmission of SARS-CoV-2 on mink farms. bioRxiv, 2020.09.01.277152 https://doi.org/10.1101/2020.09.01.277152

This paper describes an in-depth investigation of SARS-CoV-2 outbreaks on 16 mink farms, in the Netherlands, and infection in the people living or working on these farms, combining epidemiological information, surveillance data and whole genome sequencing (WGS).

97 individuals were tested by either serological assays and/or RT-PCR. 43 out of 88 (49%) of upper-respiratory tract samples tested positive by RT-PCR while 38 out of 75 (51%) of serum samples tested positive for SARS CoV-2 specific antibodies. In total, 66 of 97 (67%) of the people tested had evidence for SARS CoV-2 infection. To maintain anonymity the farms were grouped into geographic areas for analysis.

The whole genome sequences generated from mink farms and from mink farm employees were compared with the national database consisting of around 1,775 WGS. In addition, to discriminate between locally acquired infections and mink farm related SARS-CoV-2 infection, and to determine the potential risk for people living close to mink farms, WGS was also performed on 34 SARS-CoV-2 positive samples from individuals who live in the same four-digit postal code area as the first four mink farms. These local sequences reflected the general diversity seen in the Netherlands and were not related to the clusters of mink sequences found on the mink farms, giving no indication of spill-over to people living in close proximity to mink farms.

After the detection of SARS-CoV-2 on mink farms, 68% of the tested farm workers and/or relatives or contacts were shown to be infected with SARS CoV-2, indicating that contact with SARS-CoV-2 infected mink is a risk factor for contracting COVID-19.

A high diversity in the sequences from some mink farms was observed which the authors considered was most likely explained by many generations of infected animals before an increase in mortality was observed. They note that mink farms have large populations of animals which could lead to very efficient virus transmission and that the virus might replicate more efficiently in mink or might have acquired mutations which makes the virus more virulent.

A mutation in the spike protein (D614G), that has been shown to result in an increased virulence in vitro, was present in farm clusters A, C and E, but no obvious differences in clinical presentation, disease severity, or rate of transmission to humans was observed.

The authors conclude that the virus was initially introduced from humans and has evolved, most likely reflecting widespread circulation among mink in the beginning of the infection period, several weeks prior to detection.

Please note this paper has been published as a preprint on bioRxiv and has not been subject to peer review.

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