In the midst of outbreaks of COVID-19 on at least 5 mink farms in the Netherlands, a Reuters article reports that Dutch Agricultural Minister Carola Schouten issued a letter to parliament indicating that a farm worker was infected with SARS-CoV-2 from the mink. That’s a bit surprising to me, with the surprising aspect being the apparent ability to identify mink-to-human transmission. How this was determined isn’t clear and more details are needed. The nuances of what was said also are unclear. A Google translation of a Dutch news report about the case says mink-to-human transmission was “plausible” (aannemelijk), while the English Reuters report is more definitive (“A person who worked on a farm where mink are bred to export their fur contracted the coronavirus from the animals.“).
More clarity is needed.
From a biological standpoint, mink-to-human transmission wouldn’t be surprising. If mink can infect other mink, it makes sense they could also spread the virus to people in close contact (although “close contact” with farmed mink is much less common, and much less close, than human contact with pets, for example). However, identifying animal-to-human transmission when there’s widespread human-to-human transmission is a challenge, especially when people can be infected by other people with asymptomatic infections.
Figuring out exactly how a person got infected can be a challenge in the community. If someone on a farm gets sick, does that mean they got it from a co-worker, an animal or somewhere off the farm? Evaluation of the genetic sequences of the virus can help figure out who’s linked to who, as subtle changes in the virus occur over time. Finding an identical virus in two individuals supports a link, but it doesn’t tell us in which direction the virus was transmitted, or rule out the potential that both individuals were infected by the same source. The Dutch report indicates there are similarities in the gene sequences of the viruses from mink and the worker, but that still doesn’t answer the question of “who infected who.” More information about contacts between the infected worker and other workers, contact between the worker and mink, timing of contacts and disease, and genetic sequences of strains found in people off the farm in that region is needed to better understand the situation. I assume much of that will be coming, so it will be interesting to see how this story unfolds.