In a new study, researchers found examined COVID-19 infections across 16 mink farms in the Netherlands.
They found that the virus likely jumped between people and mink and back, providing strong evidence that animal to human (zoonotic) transmission is possible.
The research was conducted by a group of Dutch veterinary science experts.
The exact origin of COVID-19 is still unknown, although various theories have been put forward.
Animal experiments have shown that non-human primates, ferrets, hamsters, rabbits, and bats can be infected by SARS-CoV-2 as well as cats, dogs, lions, and tigers.
Recently, multiple outbreaks in mink farms (containing mink of the Neovison vison species) in the Netherlands have demonstrated that mink are also susceptible to SARS-CoV-2.
In the study, the team did an in-depth test of outbreaks on 16 mink farms and humans living or working on these farms, using whole-genome sequencing to underpin sources of transmission.
They describe COVID-19 infections on 16 farms, with over 720,000 animals. In total, 66 of 97 (67%) people tested had evidence for COVID-19 infection, either by PCR or serology. All people tested had a direct link to an infected mink farm.
The study showed strong evidence that at least two people on those farms were infected by minks.
The team concluded that initially the virus was introduced from humans and has evolved on mink farms, most likely reflecting widespread circulation among mink in the first SARS-CoV-2 mink farms, several weeks prior to detection.
Genetic analysis of SARS-CoV-2 from the human employees on the farms showed they were the same as those found in mink, and were not identical to those found in unrelated SARS-CoV-2 patients living in the vicinity of farms.
Genetic sequences from each of the infected mink farms fell into one of five distinct clusters, showing transmission between different mink farms.
The team says additional research will be needed to determine the routes of transmission.
At least some of these employees are very likely to have been infected directly from infected mink and thereby describe the first proven zoonotic transmission of SARS-CoV-2 to humans.
One author of the study is Dr. Bas Oude Munnink.
The study was presented at the ESCMID Conference on Coronavirus Disease.
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