Disclaimer #1 is my standard “COVID-19 is almost exclusively a human disease. Information about this virus in animals is important to investigate and consider, but don’t over-react.”
Disclaimer #2 is that this post is about another paper that’s available as a pre-print, meaning it hasn’t yet undergone peer review. However, it provides some useful new information that’s worth mentioning at this stage.
The study (Zhang et al. 2020) investigated the prevalence of antibodies to SARS-CoV-2 in cats in Wuhan, China where the COVID-19 outbreak began. One of the things we want to know is how often animals (cats, in this case) may get infected when they’re exposed to infected people. Antibodies in the bloodstream indicate the immune system has responded to the pathogen, which generally means the animal was infected at some point. Whether an infected animal can pass on the virus to someone else is a related, but separate question. This study didn’t look at the implications of infection of cats (e.g. clinical signs or transmission), just how often it occurred.
Blood samples were collected from 102 cats in animal shelters and veterinary clinics in Wuhan from January to March 2020 (i.e. during the COVID-19 outbreak). A set of 39 samples from cats that was collected from March to May 2019 (prior to the outbreak) was also studied.
- Antibodies against SARS-CoV-2 were found using an ELISA test in 15 (14.7%) of samples. Eleven of those were also positive on a second type of antibody test (virus neutralization test).
- Three of the positive cats belonged to owners known to have had COVID-19, and they had the highest antibody levels. Six were stray cats, and 6 were sampled at veterinary clinics but had no known contact with an infected owner.
- None of the cats had positive PCR results, meaning there was no evidence that the virus was still present.
- The limited knowledge of the cats’ contact with infected people limits interpretation of the results, but that’s a pretty high rate of seropositivity, especially among a group of cats that didn’t mainly consist of animals known to have been exposed to infected people.
All 39 blood samples taken from cats before the outbreak were negative. This is important to show that there’s no cross-reaction or non-specific reaction with other antibodies that may be present in the cats that would lead to a false positive result.
Overall, it’s not too surprising to see seropositive cats from infected households. If an infected person is present and cats are susceptible to infection (which we’ve already seen), it makes complete sense that seropositive animals would be found.
It was more surprising to see that high a number of positives from households without confirmed COVID-19 patients. Certainly, it’s possible that there were undiagnosed people in the households of some of them.
The strays are another interesting group. Were they pet cats that were caught as strays? Abandoned pets? In those situations, they may have been exposed to an infected owner. If they were truly feral cats, where did they get infected? Contact with people who were feeding them? Indirect contact with infected people? Other animals? It’s hard to say. We need to do more work rather than just keep speculating.
The take home messages remain the same:
- If you’re sick, stay away from animals.
- Keep your animals away from other people or animals. Social distancing applies to the whole household, not just the human members.
- Your own pet poses virtually no risk to you. If my cat is infected, he got it from me (in which case I’m already infected) or my family (who pose a much greater risk of transmission to me than the cat). If we keep pets with us but socially distanced from others, we don’t need to worry about them as sources of infection outside of the household.