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Can cats and dogs pass on the coronavirus to humans? A Cambridge researcher shares her verdict

Coronavirus? How dare you!
Coronavirus? How dare you!

Until recently, there was no suggestion that our pets could be infected with a form of coronavirus that could be passed over to humans - but then a dog in Hong Kong was found with traces of the virus from swabs in its nose and throat, setting off a predictable media frenzy.

As with so many aspects of the virus, the science took second place to the panic, until it emerged that in fact the dog’s owner had Covid-19, and it was unclear whether coronavirus was replicating in the dog or whether the dog had simply licked contaminated surfaces in the home, meaning that the virus detected on it may not have been infectious.

Then, a cat in Belgium tested positive for the viral genome, SARS-CoV-2, and Dr Sarah Caddy, post-doctoral researcher at the MRC Laboratory of Molecular Biology in Cambridge, looked into the exact circumstances. Writing in The Conversation, an online portal for academics and researchers, Dr Caddy explained that there is a cats-only strain of coronavirus.

“A cat-only coronavirus genome was discovered in the 1970s,” Dr Caddy told the Cambridge Independent this week. “Lots of cats have it and you don’t know about it. There are two forms of coronavirus: Feline Infectious Peritonitis, or FIP, which affects a small population of cats and is usually fatal, although a California team recently found some drugs which can work. FIP is generally found a couple of times a year in cats. The other strain causes mild gastrointestinal disease only.”

Other animals can also contract the virus.

“With dog coronavirus there are two different types,” Dr Caddy continues. “The first causes very mild diahorrea, the second affects the respiratory system: it’s like kennel cough, and is also mild. It’s not found in healthy dogs, but there’s no vaccine. I believe there is also a rabbit coronavirus but that has no clinical concerns. Bovine and pig coronavirus are of more importance. I’m not a large animal expert but there are vaccines around for them. Both the large animal strains have been around for decades and there is no evidence they can jump across to humans.”

However, the cat’s owner in last week’s Belgian case had tested positive for Covid-19, so when the cat developed breathing difficulties and diarrhoea a week later, it was tested for SARS-CoV-2 by vets at the University of Liège, Belgium. They found the viral genome in vomit and a stool sample. But just as for the dog in Hong Kong, the cat could simply have licked something with the coronavirus-infected particles on it - an item of clothing, for instance, or a plate - although it did also have respiratory problems. Even so, cats can develop breathing difficulties from various maladies, from feline asthma to heart disease.

Dr Sarah Caddy, a Wellcome Trust clinical research career development Fellow at the MRC-Laboratory of Molecular Biology and the Cambridge Institute for Therapeutic Immunology and Infectious Disease (CITIID)
Dr Sarah Caddy, a Wellcome Trust clinical research career development Fellow at the MRC-Laboratory of Molecular Biology and the Cambridge Institute for Therapeutic Immunology and Infectious Disease (CITIID)

“If the cat had eaten something which the owner had coughed or sneezed on, that matter doesn’t need to have gone into a cat cell, replicated and come out as as infectious,” she states.

In her article in The Conversation, Dr Caddy wrote: “The standard test for SARS-CoV-2 only detects the viral genome. It is very important to bear in mind that this test does not detect infectious or ‘live’ particles, so it is impossible to tell whether the viral genome found in the cat was from a particle that could replicate. To demonstrate infectivity, many more tests are needed. It is possible that the cat ate contaminated food and the virus simply passed through its gut. This explanation is less likely if large quantities of genetic material were detected in the cat, but this data has not been released.”

Dr Caddy remains unconvinced that pets can pass on coronavirus to humans.

“In my opinion this study doesn’t help at all,” she said on Tuesday (March 31). “It’s just scaremongering without any real evidence. This cat was sick where the Hong Kong dog wasn’t, but there are many reasons it could be sick. There was no evidence that the lungs were infected - it could be a 16-year old cat with heart failure. I’m not saying it’s wrong, just that they haven’t convinced me they’re right. These scares are completely not needed - just think what would happen to your pet if you were hospitalised with Covid-19.”

Dr Caddy is currently part of a national team “sequencing” to do with the genome.

“All institutions have shut down and switched direction to coronavirus research,” she reports.

In the meantime pet owners can be confident that their animals ‘almost certainly’ won’t give them the coronavirus.

“Hygiene is still the bottom line,” concludes Dr Caddy. “Yes, pet or pat your dog, then wash your hands.”

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