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Both theAmerican mink and theEuropean mink have shown high susceptibility toSARS-CoV-2 since the earliest stages of theCOVID-19 pandemic, first inmink farms across Europe, followed by mink farms in the United States.[1] Mortality has been extremely high amongmink, with 35–55% of infected adult animals dying fromCOVID-19 in a study of farmed mink in the U.S. state ofUtah.[2]
In November 2020, inDenmark, thegovernment mandated theslaughter of all the country's 17 million mink due to reports thata mutatedSARS-CoV-2 virus was being passed from mink to humans via mink farms, and that at least 12 human infections had been discovered inNorth Jutland. While theState Serum Institute (SSI,Statens Serum Institut) suggested that this mutation was no more dangerous than other coronaviruses, SSI head Kåre Mølbak warned that the mutation could impact the development and effectiveness ofCOVID-19 vaccines.[3][4]
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]
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]
In Denmark, there have been fiveclusters of mink variants of SARS-CoV-2; the DanishState Serum Institute (SSI) has designated these as clusters 1–5 (Danish:cluster 1–5). In Cluster 5, also referred to asΔFVI‑spike by the SSI,[8] several different mutations in thespike protein of the virus have been confirmed. The specific mutations include 69–70deltaHV (a deletion of thehistidine andvaline residues at the 69th and 70th position in the protein), Y453F (a change fromtyrosine tophenylalanine 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 inMichigan, resulting in four human infections that were largely kept from public view upon their discovery late 2020, and only announced by theUS Centers for Disease Control (CDC) in March 2021, was deemed ancestral to theOntario WTD clade spillover event fromwhite-tailed deer nearly a year later inOntario, 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]
[...] (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
