We have a lot of different concerns about SARS-CoV-2 on mink farms. Mink are really susceptible and human-mink infection isn’t uncommon, so if we continue to farm mink, we will continue to expose mink as long as this virus is around.
Two of the biggest concerns relate to the potential for mink to make things worse in the big picture.
- Development of mutations that lead to new variants of concern (VOCs) after spread back to people
- Spread to other species
I’ll focus on #2 here.
We want COVID-19 to be a human-only disease. If it gets established in animal populations, especially wildlife, that changes the game. I doubt we’re going to eradicate this virus but if it develops animal reservoirs, there’s no chance whatsoever.
Further, if it gets established in animals, we may have to deal with greater risk of VOCs. VOCs are worsening and dragging out this pandemic and with more transmission (in animals or people), there will be more VOCs. Mutations are a normal event when viruses replicate. The more a virus spreads, the more mutations that occur, and the greater chance that a mutation that impacts transmissibility, virulence or vaccine evasion emerges.
For a virus to establish in animals, a few things need to happen:
- Animals have to be exposed, directly or indirectly, to infected people.
- The animal species has to be susceptible to the virus, and able to transmit it.
- The species must live in large enough groups for sustained transmission within the species.
- Then, there has to be a mechanism to spread it back to people.
That might seem like a tough list, but it’s not impossible (and that’s what happens with some other zoonotic viruses).
So, we want to keep this virus away from animals, particularly wildlife.
This is where we come back to mink.
A recent paper in Transboundary and Emerging Diseases (van Aart et al) reports on surveillance on mink farms in the Netherlands, a country that identified SARS-CoV-2 infection in over half of their mink farms.
- 13 farm dogs and 101 cats (largely feral…69 adults and 32 kittens) on 10 farms were tested.
- SARS-CoV-2 was detected by PCR in 3 (4.4%) adult cats and 1 (7.7%) dog.
- Since PCR testing just tells you a single point-in-time result, antibody testing was used to identify prior infection. 18% of adult cats, 0% of kittens and 2 (15%) dogs had evidence of previous infection.
- When PCR and serological results are combined, 19.4% of adult cats and 15% of dogs had evidence of infection.
That’s pretty impressive.
There’s no guarantee that all were exposed from mink vs infected farm workers, but mink-cat transmission seems reasonable since these were feral cats that would not have interacted closely with people. Source of infection of dogs is probably harder to tease out since they presumably had closer contact with farm personnel.
Interestingly, none of the 9 domestic cats that were tested were positive, despite having infected owners. Infection was only found in the feral cats. Whether all were infected via mink or some was subsequent cat-cat transmission (a likely scenario) is also impossible to discern.
Mink-cat infection would have been through indirect exposure, and raises concerns that other species could have been similarly infected, including small mammals like mice. That could be from the mink (most likely indirectly) or from cats (e.g. mouse surviving an encounter with an infected cat).
These concerns are why there is surveillance around many infected mink farms. That type of work has also found SARS-CoV-2 in ‘wild’ (or, more likely, previously escaped) mink.
What’s the relevance?
- It’s hard to say.
However, it supports plausible concerns about animal-animal transmission and the need to reduce exposure to animals.
Ultimately, the best way to reduce the risks associated with animals is to control this disease in people.
Vaccination of mink is a consideration, and I’ve written about that recently.
Overall, this shows the importance of the “One Health” approach and a need to be proactive to identify and hopefully prevent problems, rather than our typical reactionary approach whereby we wait for definitive proof of an animal aspect before putting any real effort in.