Transmission of SARS-CoV-2 on mink farms between humans and mink and back to humans

Abstract

Animal experiments have shown that non-human primates, cats, ferrets, hamsters, rabbits and bats can be infected by SARS-CoV-2. In addition, SARS-CoV-2 RNA has been detected in felids, mink and dogs in the field. Here, we describe an in-depth investigation using whole genome sequencing of outbreaks on 16 mink farms and the humans living or working on these farms. We conclude that the virus was initially introduced from humans and has since evolved, most likely reflecting widespread circulation among mink in the beginning of the infection period several weeks prior to detection. Despite enhanced biosecurity, early warning surveillance and immediate culling of infected farms, transmission occurred between mink farms in three big transmission clusters with unknown modes of transmission. Sixty-eight percent (68%) of the tested mink farm residents, employees and/or contacts had evidence of SARS-CoV-2 infection. Where whole genomes were available, these persons were infected with strains with an animal sequence signature, providing evidence of animal to human transmission of SARS-CoV-2 within mink farms.

Therapeutically administered ribonucleoside analogue MK-4482/EIDD-2801 blocks SARS-CoV-2 transmission in ferrets

“…Furthermore, SARS-CoV-2 RNA was present at low copy numbers in the intestinal tissue samples and rectal swabs of the vehicle source animals as well as their contacts but undetectable in the MK-4482/EIDD-2801-treated source group and co-housed contact animals. Phylogenetic analysis of outbreaks in mink farms revealed prolonged intra-colony circulation and zoonotic mink-to-human transmission 9 , leading us to select ferrets-members of the weasel genus closely related to minks-as a SARS-CoV-2 transmission model. We noted that the experimental infection of ferrets was strongly dependent on the amount of viral inoculum used.…”

“…Spill-back of SARS-CoV-2 to farmed minks, subsequent large-scale mink-to-mink transmission and, in some cases, zoonotic transmission back to humans revealed efficient viral spread among members of the weasel genus without previous adaptation [6][7][8][9] . Although mink farms reported elevated animal mortality and gastrointestinal and respiratory clinical signs 15 , outbreak follow-up revealed continued intra-colony spread for extended periods of time 9 , suggesting that the acute clinical signs in the majority of infected animals may be mild. These mink field reports corroborated results obtained with experimentally infected ferrets showing that mustelids of the weasel genus transmit SARS-CoV-2 efficiently without strong clinical disease manifestation 16,17 .…”

Assessing the Risks of SARS-CoV-2 in Wildlife

“…Naturally acquired infections of SARS-CoV-2 have only been demonstrated in pet dogs and cats in domestic settings, in tigers (Panthera tigris), lions (Panthera leo) and a puma (Puma concolor) in zoological collections, and in farmed American mink (Neovison vison) [38,39,40,41]. All such cases of natural infection have been linked to initial transmission from humans to the animals in their care.…”

“…Sequencing of viral genomes has shown that natural transmission has taken place amongst farmed mink following initial introductions by infected workers [38,39]. Transmission amongst separately housed mink suggests that the infection may have been spread by fomites, respiratory droplets or contaminated dust from bedding [39].…”

“…There have been many cases of SARS-CoV-2 in farmed mink with infections reported from Europe and the USA [75]. Transmission among mink and spillback to humans have been confirmed [38,39], including the emergence of a new variant of SARS-CoV-2 in communities adjacent to mink farms in North Jutland, Denmark [76]. Escaped mink and the presence of other free-living mammals (e.g.…”