An abstract in the upcoming ECCVID Conference (ESCMID conference on coronavirus disease) has some of our very preliminary Canadian dog/cat surveillance data (Beinzle, Marom and Weese, SARS-CoV-2 infection in pets). A press release went out about it from the conference that’s been picked up by various news agencies, resulting in some articles about the study that are a bit alarmist. As is typical with zoonotic diseases, we’re trying to walk the fine line between raising awareness and preventing people from over-reacting.
Before I get to the details, I’ll give the overall synopsis of our results to date to provide some very important perspective first:
- Transmission of SARS-CoV-2 to pets probably isn’t uncommon. That’s not big news. We know cats, in particular, are susceptible to infection. With limited surveillance, a reasonable number of infected pets have been identified. I’ve been saying for a while that transmission to pets was likely occurring under the radar, but it’s not likely a big deal – it’s something to watch and figure out over time, but not to freak out about.
- Pets in households with human COVID-19 cases are unlikely to be shedding the virus at any given time. While they can be infected, the window that they’ll shed the virus is likely pretty short. That’s why we have a hard time finding positive animals through PCR testing (looking for the virus) vs antibodies (looking for evidence of previous infection).
- Relax. The messages are the same: treat pets like other members of the family when it comes to control measures for this virus. If the people in the household are isolating, the pets should too. If someone is staying away from people because they might have COVID-19, they should stay away from animals too.
- The health impact of SARS-CoV-2 infection in pets is still unclear. I suspect cats are somewhat similar to people (with fewer infections). Most don’t get sick. Most that get sick get mild flu-like disease. A small percentage may get more seriously ill. It’s still a bit of a guess but I think it’s reasonable.
OK… now here are the details of our preliminary Canadian study results.
We looked at two things: testing for the virus itself, and testing for antibodies in pets.
- We looked for viral RNA using PCR on swabs of the nose, mouth and rectum of pets in contact with people infected with COVID-19. We did this by going into the homes of these people and sampling the pets around the time of human illness. Of the 36 animals tested, 18 dogs, 16 cats and 1 ferret were negative. We got inconclusive results from one cat, and based on the timing of the owners’ and cat’s illness, we suspect it was sampled late in infection (so not shedding enough virus to give a definitive positive result).
- We also tested pets for antibodies against the SARS-CoV-2 virus. Antibodies indicate previous infection. We’re still early in the process on this phase of the research, but antibodies were present in 4/8 (50%) cats and 2/10 (20%) dogs. Samples from animals from 2019 (pre-COVID) were all negative, including cats with feline coronavirus infection (so we know the antibody test does not cross-react). All of the seropositive cats were reported to have been sick around the time of the owners’ illness. Take that with a grain of salt because it’s retrospective, but it’s interesting.
The 50% and 20% seropositive results are high, but maybe not too surprising, and I don’t really focus on the specific percentages because the sample size is small. The key is antibodies are not uncommon in these animals, which supports that cats seem to be fairly susceptible to infection. Our numbers are currently higher than the few other recent studies, but not out of line. A study from Wuhan, China showed 14.7% of cats sampled in early 2020 were seropositive. That study included testing of stray cats, not just cats from known positive households like we did. It’s possible that some were pet cats that had been released or were indoor-outdoor cats, but they weren’t all known to have been exposed. Another study reported antibodies in 3.4% of dogs and 3.9% of cats in Italy. This involved sampling of healthy pets in veterinary clinics, rather than targeting positive households. So, our study population was a lot higher risk, and therefore a higher prevalence of antibodies in our sample makes sense.
The relatively good state of COVID-19 in our area over the summer hurt the study (but I’m not complaining) since we didn’t have many human cases in the area with pets we could test. As we ramp up in the second wave, we’ll unfortunately be in a better position to get more samples. We’re also working on a few ways to get more blood samples from pets of people who had COVID-19 earlier in the year. We’ll hopefully have more robust results soon.