How did Covid-19 get onto Dutch mink farms?

Abstract

FARM workers and drivers were the likely cause of a SARS-CoV-2 outbreak on mink farms in the Netherlands during 2020, new research suggests. The outbreak, which affected over half of the mink farms in the country between April and November 2020, was largely spread by workers, say a team of researchers from the UK and the Netherlands, with cats, dogs and wild animals (such as badgers) living around mink farms also potentially having played a role in the spread of coronavirus between the farms. The study, published recently in Nature Communications, analysed the genome sequences of SARS-CoV-2 isolated from minks and farm workers on 64 infected farms. Scientists sought to investigate the timing of virus introduction into different farms and how the virus spread from farm to farm. They compared the rate at which the virus mutated when spreading between farms with the mutation rate in the wider population. The analysis revealed five virus clusters, each representing a separate introduction of the virus into farms, with the first occurring in April 2020. The researchers found that a mutation in the largest cluster led to faster disease evolution, with wider and longer spread of the virus than in the other clusters, affecting 40 farms across 15 municipalities. Scientists identified farms from which the virus was most likely to have spread by quantifying transmission patterns. Farms near infected farms were more likely to become infected than those further away, the study reports, with the movement of people being a statistically significant predictor of virus dispersal. The virus jumped back and forth between minks and people on several farms, but the spread from mink farms back into local communities was limited, scientists concluded. “There is a risk that infected animals become virus reservoirs that can infect people in the future Researcher Samantha Lycett, group leader in pathogen phylodynamics at the University of Edinburgh's Roslin Institute, explained how ‘combining data from the virus genome with information on virus evolution’ helped to paint a picture of how SARS-CoV-2 spread between the mink farms. ‘This approach could be used to understand and predict outbreaks of this and other viruses,’ she said. Lu Lu, a postdoctoral research associate at Edinburgh's Usher Institute, added: ‘There is a risk that infected animals become virus reservoirs that can infect people in the future. It is fundamental to keep monitoring the situation and to prevent the virus from being reintroduced into mink farms and spread to humans.’ Following the banning of fur farming in the Netherlands in January 2021, no further cases of coronavirus in minks have been reported.