Both the American mink and the European mink have shown high susceptibility to SARS-CoV-2 since the earliest stages of the COVID-19 pandemic, first in mink farms across Europe, followed by mink farms in the United States.[1] Mortality has been extremely high among mink, with 35–55% of infected adult animals dying from COVID-19 in a study of farmed mink in the U.S. state of Utah.[2]
The first known transmission of SARS-CoV-2 among wild mink was reported in Utah, which researchers believed was due to contact with infected captive mink rather than through an intermediary vector in the wild or direct human-to-mink transmission.[1] Tracking the origin and spread of mink-related COVID variants has proven more difficult in the United States, where the reporting of outbreaks on mink farms has been voluntary, as opposed to the mandatory screening procedures introduced during outbreaks in Denmark and the Netherlands.[5]
Transmission
Due to the mink ACE2 receptor being a similar or better fit for SARS-CoV-2 compared to humans and the cramped living conditions of farm-raised animals, mink readily transmit SARS-CoV-2 to one another and develop symptoms of COVID-19.[6] Additionally, Dutch researchers determined that the bedding materials and airborne dust on mink farms with outbreaks had also become highly contaminated.[7]
Mutations and variants
In Denmark, there have been five clusters of mink variants of SARS-CoV-2; the Danish State Serum Institute (SSI) has designated these as clusters 1–5 (Danish: cluster 1–5). In Cluster 5, also referred to as ΔFVI‑spike by the SSI,[8] several different mutations in the spike protein of the virus have been confirmed. The specific mutations include 69–70deltaHV (a deletion of the histidine and valine residues at the 69th and 70th position in the protein), Y453F (a change from tyrosine to phenylalanine at position 453, inside the spike protein's receptor-binding domain), I692V (isoleucine to valine at position 692), M1229I (methionine to isoleucine at position 1229), and a non-conservative substitution S1147L.[9][8][4]
In North America, a mink-human spillover event in Michigan, resulting in four human infections that were largely kept from public view upon their discovery late 2020, and only announced by the US Centers for Disease Control (CDC) in March 2021, was deemed ancestral to the Ontario WTD clade spillover event from white-tailed deer nearly a year later in Ontario, Canada.[10][11][12] The Michigan spillback into humans was the first documented case of any animal spillback in the United States.[13]
In late 2022, scientists continued to monitor residual Delta strains, such as Delta strain AY.103, which have picked up Omicron mutations during co-infection in mink and deer and form the potential for so-called "Deltacron" spillover events. These hybrid strains could potentially combine the increased fatality rate of Delta with the enhanced transmissibility of Omicron.[14]
^ abGrove Krause, Tyra. "Mutationer i minkvirus" (in Danish). Statens Serum Institut. Archived from the original on 7 January 2021. Retrieved 6 November 2020.
^de Rooij, Myrna; Hakze-Van der Honing, Renate; Hulst, Marcel; Harders, Frank; Engelsma, Marc; van de Hoef, Wouter; Meliefste, Kees; Nieuwenweg, Sigrid; Oude Munnink, Bas; van Schothorst, Isabella; Sikkema, Reina; van der Spek, Arco; Spierenburg, Marcel; Spithoven, Jack; Bouwstra, Ruth; Molenaar, Robert-Jan; Koopmans, Marion; Stegeman, Arjan; van der Poel, Wim; Smit, Lidwien (December 2021). "Occupational and environmental exposure to SARS-CoV-2 in and around infected mink farms". Occupational & Environmental Medicine. 78 (12): 893–899. doi:10.1136/oemed-2021-107443. PMC8327637. PMID34330815.
^ abLassaunière, Ria (11 November 2020). "SARS-CoV-2 spike mutations arising in Danish mink and their spread to humans". Statens Serum Institut. Archived from the original on 10 November 2020. Retrieved 11 November 2020. [...] (hereafter referred to as ΔFVI-spike). [...] These include: i) 69-70deltaHV – a deletion of a histidine and valine at amino acid positions 69 and 70 in the N-terminal domain of the S1 subunit; ii) I692V – a conservative substitution at position 692 that is located seven amino acids downstream of the furin cleavage site; iii) S1147L – a non-conservative substitution at position 1147 in the S2 subunit; and iv) M1229I – a conservative substitution located within the transmembrane domain
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