I tweeted recently about the first report of the B.1.1.7 SARS-CoV-2 variant being found in animals, specifically in a dog and cat in Texas, which deserves some more discussion. Also a new pre-print article (i.e. non-peer-reviewed paper) was posted recently that will probably raise more concerns, so I figured I’d better write about that one too.
The B.1.1.7 variant of SARS-CoV-2, which first emerged in the UK, is becoming widespread internationally and fueling third waves of COVID-19 in the human population in multiple countries. It’s more transmissible than “regular” SARS-CoV-2 and may cause more severe disease. Fortunately most of the available vaccines still seem to be effective against it, but it’s causing a lot of damage while we’re still trying to get enough people vaccinated.
It’s clear that people commonly pass SARS-CoV-2 to their pets. As this strain (and others) become more common in people, it’s inevitable that animals (particularly the pets we live with) will be exposed too. It’s unlikely (though possible) that the strain will be significantly less infective in animals than the original strain, so we fully expect to see it spillover into pets. I assume there have been thousands of dogs and cats unknowingly infected with this and other variants of concern (VOCs) so far, but we test very few animals in COVID-19-affcected households. So, the Texas report was an expected confirmation that pets can also be infected with this VOC. We’re testing animals here in Canada too as part of our ongoing surveillance project.
This paper, which I will emphasize again has yet to be peer reviewed, will likely cause a bit of concern, but probably unnecessarily.
The authors observed an increase in dogs and cats presented to a referral veterinary clinic in the UK with myocarditis (inflammation of the heart). The concern was that the increase occurred at the same time the B.1.1.7 variant was surging through the human population in the UK.
- Clinical observations of abnormal patterns are important. Most often, they end up being nothing remarkable – just random changes in normal events, or coincidences. Sometimes, though, they’re an early warning that something is going on. So, they are worth investigating.
Most owners of the affected animals reported having COVID-19 themselves in the 3-6 week period preceding the animals’ illnesses.
- Interesting. Far from definitive (especially during a pandemic when lots of people are infected), but worthy of investigation.
They collected oro-nasal and rectal swabs from six cats and one dog with myocarditis in late January / early February. They also collected blood from these pets to look for antibodies against SARS-CoV-2. Blood samples were also collected from 4 other pets (2 cats, 2 dogs) that were recovering from myocarditis. None of the animals were reported to have had any respiratory disease.
- 3 animals (2 cats and 1 dog) were positive on PCR for SARS-CoV-2 on rectal swabs, with a low viral load. All oro-nasal swabs were negative. The PCR test that was used indicated that the B.1.1.7 variant was present, although the test performance isn’t described.
- Antibodies against SARS-CoV-2 were not detected in these 3 pets. That makes the results a challenge to interpret. Were the PCR results false positives, or were the serology results false negatives? It doesn’t seem like they followed up with later antibody testing of PCR-positive animals. That would help determine if they were antibody negative initially simply because they had not yet produced enough detectable antibodies (as that can take some time).
- Three other animals (2 cats and 1 dog) had antibodies against the virus. Those animals were either PCR-negative (1) or PCR was not done (2). If the serological test used was good (no information was provided on test performance or quality control), then I’d assume the PCR-negative, serology-positive animals had been infected at some point in the past. PCR is only positive for a short period of time when the animal is actively infected and shedding virus, but antibodies can stick around for a long time after the infection is gone.
What does this tell us?
- That some human-to-pet transmission of SARS-CoV-2 likely occurred (but we already know this happens).
- The B.1.1.7 variant was involved (ditto).
Overall, 6/11 animals had some degree of evidence of exposure to SARS-CoV-2. That seems like a fairly high proportion, but it’s not far off the numbers we’re seeing with our work and work from other groups in healthy animals from COVID-19-positive households. So this does not provide any evidence of a link between SARS-CoV-2 infection in pets and myocarditis. Nonetheless, I wouldn’t dismiss it, and we should look into it more.
The authors’ statement that “the discovery of B.1.1.7 infected cats and dogs highlights more than ever the risk that companion animals may potentially play a significant role in SARS-CoV-2 outbreak dynamics than previously appreciated” has no substance. This study just showed that animals can be infected. It does not indicate anything about pets’ role in outbreak dynamics or anything else. We don’t want to ignore the potential that cats, in particular, could transmit the virus. However, their conclusion is unsupported and unlikely to be true.
I’m fully on board with their last statement, though: “Therefore, there is an urgent need to greatly accelerate and strengthen the investigations and surveillance of animal infections by highly-transmissible variants such as British B.1.1.7, South-African B1.351 and Brazilian P.1 variants as part of the global response to the ongoing multi-species COVID-19 pandemic.”