Based on what we knew from the original SARS virus and the similarity with SARS-CoV-2 (the cause of COVID-19), we expected ferrets to be one of the species that could be susceptible to infection with the latter. When ferrets were infected with the SARS virus, they got sick (unlike cats that just shed the virus). Various experimental studies are underway internationally to look at susceptible species, both to understand the virus but also in large part to develop an experimental model (for things like vaccine research).
So, it’s not surprising to see that ferrets are susceptible to SARS-CoV-2 infection, as described in a pre-proof manuscript from the journal Cell Host & Microbe (Kim et al. 2020). It’s a small but important study.
The short version:
- Ferrets were experimentally infected and developed fever, lethargy and cough.
- Ferrets in direct contact with infected ferrets got sick too.
- Ferrets in adjacent cages got infected (i.e. virus was passed to them) but they didn’t get sick, showing that the virus was spread by indirect contact, but that the amount of virus spread this was was probably low and not enough to cause disease.
The longer version:
- They inoculated 2 ferrets intranasally with the virus. Two days later, they put some uninfected ferrets in the same cages and put some other uninfected ferrets in adjacent cages.
- This was repeated three times (6 infected and 12 exposed in total, plus 6 uninfected ferrets as controls).
- Blood, nasal washes, saliva, urine and feces were tested for the presence of the virus every other day for 12 days.
- After inoculation, ferrets developed a fever, decreased activity and occasional coughs. None died. Virus was detectable by day 2 after infection and viral levels were highest in nasal secretions. (That’s not surprising.)
- Peak viral levels were on day 4 and persisted to day 8. All were negative at day 10. In addition to nasal shedding, lower levels of virus were found in saliva, feces and urine on days 2-8. Low levels were found in blood for a shorter period of time.
- In addition to detection of viral nucleic acids (i.e. not necessarily live virus) by PCR, live virus was also isolated.
- That’s not surprising since infected ferrets were able to pass the virus on to other ferrets, but is an important finding nonetheless. Studies that involve PCR always end up raising questions about whether live or dead virus was detected. Virus was also found in tissue samples from another group of infected ferrets. Overall, there’s no doubt these ferrets were truly infected.
- All 6 ferrets that had direct contact with the infected ferrets developed fevers and decreased activity. These ferrets were all infected, as virus was detected in nasal samples by day 4 after they were put into contact with the experimentally infected ferrets. Virus was also found in saliva and feces.
- None of the indirect contact ferrets (those in adjacent cages) showed any signs of illness. However, they were infected. This raises a few interesting points:
- One is the potential for aerosol transmission (the authors say “airborne’” but I assume that’s unlikely and I’ll bet there will be some debate over their use of that term).
- The other is that the lower level of exposure from indirect contact possibly accounted for the lack of disease (although we can’t get too carried away with conclusions based on what happened to 6 healthy adult ferrets).
- By 12 days after infection, all ferrets were back to normal.
This study was focused on seeing if ferrets would be a good experimental model (and it looks like they would be, getting consistently sick but not seriously ill).
What does this mean for pet ferrets and their owners?
Not much beyond what we’ve already said.
- If you’re sick, stay away from your ferret.
- If a ferret is exposed to an infected person, keep it away from other people (and other pets).
- Veterinarians should continue to ask owners about household COVID-19 exposure to help protect themselves from the owners, but also to consider potential issues when caring for their pets.