I’ve spent a lot more talking about mink in the past few months than I ever thought I would. In regard to SARS-CoV-2 (the virus that causes COVID-19 in people), mink and ferrets (their close relatives) are a fascinating story, but I’ll try to be brief about it. Mink have become important because of the widespread outbreaks of SARS-CoV-2 on mink farms in some countries, and ferrets are important because they’re household pets and appear to be equally susceptible to the virus.  What we know about these two species within the mustelid family is quite different. We have good experimental data for ferrets and very little field data. For mink, it’s the opposite.

What’s the story with mink and SARS-CoV-2?

I think it’s fair to say this caught us off guard. At the start of the COVID-19 pandemic, no one was talking about risks to/from mink farms. Yet, mink are highly susceptible to the SARS-CoV-2 virus. There have been widespread outbreaks on mink farms in some countries, first in the Netherlands but now in several countries in Europe, as well as in the US. In the vast majority of cases, it is suspected that the mink were initially infected by a person, and then the virus spread further from animal-to-animal.  Some affected farms have had few health issues while others have reported considerable illness and increased mortality in their animals, which has led to widespread culling of mink in some countries to try to contain the spread of the virus.

There are a few additional concerns with these outbreaks beyond the health of the animals themselves. One is zoonotic transmission back to people, as apparent mink-to-human transmission has been reported in one Dutch study. Infection of feral cats on mink farms has also been identified, which raises concern about the cats (or escaped mink) potentially infecting wildlife in the surrounding area.  Work on this issue is ongoing.

So, mink can be infected, the virus is effectively spread between mink, mink can potentially infect people in contact them, and mink may be a source of exposure for other animals. All of those are concerning.

How about ferrets and SARS-CoV-2? Are they as susceptible as mink?

Whether ferrets are “as susceptible” as mink is hard to say; however, they are clearly susceptible to infection, can get sick, and can shed enough virus to infect other ferrets, as has been demonstrated in multiple experimental studies. Notably, ferrets can be infected with fairly low doses of SARS-CoV-2.

One thing that raised some concern and confusion was a report that ferrets could spread the virus “via the air.” While the study showed that ferrets were able to transmit the virus to other ferrets in cages 10 cm away, the results weren’r actually indicative of true airborne spread (a bit of a loaded term). Rather, it was likely droplet spread over a short distance. A more recent study raised a bit more concern, as it  reported transmission of the virus between ferrets over more than 1 metre. In this study, airflow was high and was directed from the infected to uninfected ferrets, so while the virus traveled at least 1 metre under those conditions, we have to be careful when assessing what that means. I think it supports the fact that this virus can move in the air for short distances, but a lot of factors influence how far it goes and the risks associated with aerosol transmission. We’re learning more and more than ventilation and environmental conditions are important for human-to-human transmission as well.

How sick can ferrets get from SARS-CoV-2?

At the start, I was expecting ferrets to be susceptible to severe disease because ferrets can also get quite sick, and sometimes die, after infection with the original SARS virus. The SARS-CoV-2 doesn’t seem quite as hard on them, but experimental data are variable. Some studies have reported infections with limited or no obvious signs of disease (Shi et al.,  Schlottau et al., Kim et al.)  However, at least one study reported more serious disease from SARS-CoV-2 in ferrets, sometimes requiring euthanasia. The difference in results might be related to the dose of virus, with higher doses used in the experimental study where more serious disease was observed.

If ferrets are susceptible to SARS-CoV-2, why aren’t there reports of infected pet ferrets?

Good question. That probably relates to limited testing. In our Canadian SARS-CoV-2 surveillance study, we’ve only been able to test one ferret. I haven’t seen much other surveillance data in this species. There’s one pre-print study looking at human-to-ferret transmission in a household where there were two infected people and 29 ferrets, but they didn’t find any evidence of transmission to ferrets. However, it’s hard to conclude much from a study of one household. Testing of the ferrets started 16 days after the onset of the first person’s illness and 13 days after the onset of the second person’s illness. It’s a challenge getting samples from the animals early in the disease of the people, so we probably under-estimate transmission with studies like this (ours included). The same study looked for antibodies in the ferrets too, but it was antibodies from oral swabs that were submitted for virus testing, and I’m not sure anyone knows how sensitive that technique is. So, there was no evidence of human-to-ferret transmission, but it was only one household and the testing had some significant limitations. Study of more ferrets in more households is needed. The lack of reports of infected ferrets may also be a function of there being fewer pet ferrets compared to dogs/cats, and correspondingly less testing for that reason as well.  Ferrets seem to be more susceptible than dogs and cats in experimental studies.

Can ferrets infect people with SARS-CoV-2?

We don’t know.  Given their susceptibility to the virus, the experimental study data and evidence of potential transmission of SARS-CoV-2 from mink to people, I think we have to assume that an infected ferret might pose some degree of risk to people as well. However, if a ferret is infected, it almost certainly got it from a human household contact, and that person poses much more risk to others in the household than the ferret does. The main risk is if the ferret leaves the household (e.g. to see a veterinarian) during the period when people in the household are infected, as it may take the virus along for the ride and could then potentially spread it to others.

What should be done with mink and ferrets?

• Anyone with COVID-19 should absolutely not go near a mink farm (or anyone who works on a mink farm). That’s the big one.

The same general approach that we recommend for dogs and cats applies to ferrets:

• If you have COVID-19, try to limit or avoid contact with your ferret.
• If your ferret has been exposed to someone with COVID-19, keep it away from other people or animals.
• If your ferret has been exposed to someone with COVID-19 and is sick, let your vet know.  Discuss what to do over the phone, at least initially, rather than showing up to the veterinary clinic with your ferret.

Next up for animal reviews: Horses

Image source: https://www.cbc.ca/news/canada/newfoundland-labrador/covid-outbreaks-mink-farms-canadian-breeders-prepare-1.5769815