In the Netherlands, two-way transmission of SARS-CoV-2 transmission on mink farms

In the Netherlands, whole genome sequencing of SARS-CoV-2 outbreaks on 16 mink farms has revealed virus transmission between human to mink, as well as from mink to human. The virus was initially introduced from humans, the study's authors say, and it has since evolved. "More research in minks and other mustelid species is important to understand if these species are at risk of becoming a reservoir of SARS-CoV-2," they write.

Although several animals have been shown to be susceptible to SARS-CoV-2, the zoonotic origin of the SARS-CoV-2 pandemic is still unknown. In the Netherlands, the virus was first diagnosed on two mink farms in late April of 2020. In response, the Dutch national response system for zoonotic diseases was activated, and an extensive surveillance system was set up.

Bas B. Oude Munnink et al. performed an in-depth investigation among the first 16 infected mink farms in the Netherlands. Their analysis combined SARS-CoV-2 diagnostics, whole-genome sequencing and in-depth interviews with farm workers. By the end of June, 66 of 97 (68%) of the mink farm residents, employees and/or contacts tested had evidence for SARS-CoV-2 infection. Analysis of the mink virus genomes on these farms revealed a diversity of sequences.

These large clusters of infection were initiated by human COVID-19 cases with viruses that bear the D614G mutation, say the authors. Sequencing also revealed that some people were infected with strains of the virus with an animal sequence signature, providing evidence of animal to human transmission. Further analysis indicated no spillover to people living in close proximity to mink farms. They authors write: "It is imperative that fur production and trading sector should not become a reservoir for future spillover of SARS-CoV-2 to humans."