In the first wave of the COVID-19 pandemic (April 2020), SARS-CoV-2 was detected in farmed minks and genomic sequencing was performed on mink farms and farm personnel. This study describes the outbreak and uses sequence data with Bayesian phylodynamic methods to explore SARS-CoV-2 transmission in minks and humans on farms. A high number of farm infections (68/126) in minks and farm workers (>50% of farms) were detected, with limited community spread. Three of five initial introductions of SARS-CoV-2 led to subsequent spread between mink farms until November 2020. Viruses belonging to the largest cluster acquired an amino acid substitution in the receptor binding domain of the Spike protein (position 486), evolved faster and spread longer and more widely. Movement of people and distance between farms were statistically significant predictors of virus dispersal between farms. This study provides novel insights into SARS-CoV-2 transmission between mink farms and highlights the importance of combining genetic information with epidemiological information when investigating outbreaks at the animal-human interface.

Lu Lu, Reina S. Sikkema, Francisca C. Velkers, David F. Nieuwenhuijse, Egil A. J. Fischer, Paola A. Meijer, Noortje Bouwmeester-Vincken, Ariene Rietveld, Marjolijn C. A. Wegdam-Blans, Paulien Tolsma, Marco Koppelman, Lidwien A. M. Smit, Renate W. Hakze-van der Honing, Wim H. M. van der Poel, Arco N. van der Spek, Marcel A. H. Spierenburg, Robert Jan Molenaar, Jan de Rond, Marieke Augustijn, Mark Woolhouse, J. Arjan Stegeman, Samantha Lycett, Bas B. Oude Munnink, Marion P. G. Koopmans