Here’s a quick update on some recent feline studies on SARS-CoV-2. Some come with the increasingly common disclaimer that they are pre-prints, meaning the studies haven’t yet undergone peer review by other scientists in the field.
Cats in Hong Kong (Barrs et al. Emerg Infect Dis 2020)
This study has undergone peer review, and provides a nice description of Hong Kong’s efforts early in the pandemic. They had the most comprehensive response to potential animal exposure, and this information is available as a result of their approach to quarantine and test pets of infected people early in the pandemic, when alternate housing was not available.
They tested 50 cats from households with COVID-19 patients, or where owners had close contact with an infected person. They detected SARS-CoV-2 by PCR in 6 (12%) of the cats. They sequenced the viral isolates from a person and a cat in one household, and they were (unsurprisingly) identical, supporting the conclusion that one infected the other (presumably human-to-cat).
Dogs and cats in France (Fritz et al. 2020)
This pre-print describes a study of dogs and cats from COVID-19-positive households in France. They used a battery of antibody tests to detect previous exposure to the virus (as compared to PCR testing, which aims to detect active infection by finding pieces of the actual virus). They ran 4 tests: a neutralizing assay and 3 tests looking for IgG against three different viral proteins.
- If a positive is considered an animal that was positive on either the neutralization assay OR all 3 IgG tests, 8 of 34 (24%) cats and 2 of 13 (15%) dogs were positive.
- If a positive is considered an animal that was positive on ANY one of the tests, the numbers jump to 59% in cats and 39% in dogs.
- Only 1 of 16 cats and 0 of 22 dogs from non-COVID-19 households were positive using the first criterion (whether that means the one household had undetected COVID-19 in a person, that the cat was exposed outside the house, or the result was a false positive isn’t possible to discern). Using the second criterion there were 6 (15%) positive animals in this group. That’s high for a negative control group, but substantially less than from the COVID-19 households.
The seroprevalence is high, but consistent with what we have found so far with our serological studies of dogs and cats in Canada (4/8 cats, 2/10 dogs), supporting fairly common human-to-pet transmission.
Another cat experimental study (Gaudreault et al. 2020)
Another pre-print, this one doesn’t add much to what we already know, but beefs up our overall knowledge. They took 6 cats (4-5 months old) and exposed them to the SARS-CoV-2 virus through the nose or mouth. They then added naive cats one day later to look for cat-to-cat transmission. All pretty standard. Cats stayed clinically healthy but there was evidence of infection via detection of the virus in tissues and some signs of inflammation in the airways. Transmission to the other cats occurred within 2 days.
So, it’s similar to what we’ve already heard: cats can be infected, they don’t usually get noticeably sick, but they can infect other cats.
Cats: A Case Report (Hosie et al. 2020)
This is a pre-print case report of two cats with SARS-CoV-2 infection in the UK.
The first case was a 4-month-old kitten whose owner had COVID-19. A couple of weeks after the onset of the owner’s illness, the kitten was taken to a veterinarian with severe respiratory disease. The kitten’s condition deteriorated and it was euthanized. There were signs of severe respiratory disease on radiographs, and necropsy results were consistent with severe viral pneumonia. SARS-CoV-2 was identified in the lung, and no other potential causes were identified.
They researchers then tested 387 swabs that were submitted to the University of Glasgow diagnostic lab for respiratory pathogen testing. One of these was positive for SARS-CoV-2. This was from a 6-year-old cat with mild respiratory and ocular disease. It was also positive for feline herpesvirus, a common cause of those signs in many cats. However, one of the cat’s owners had signs consistent with COVID-19 at the time the cat was sick. Most likely, SARS-CoV-2 infection was an incidental finding here.
Taken together, these reports are consistent with our current messaging:
- Cats are susceptible to the SARS-CoV-2 virus.
- Most often, infections are likely subclinical (i.e. cats stay healthy).
- Just like in people, some cats can get sick, including (rarely) fatal illness.
- Cats can spread the virus cat-to-cat, so we have to consider cat-to-human transmission a possibility (however uncommon).
- Most cats that get infected are directly infected by their owners.