Can Animals Catch SARS-CoV-2 and get COVID-19 Infection?

An interesting article published by Patterson and others as a pre-print looked at 817 companion animals living in Northern Italy who were sampled at the same time there was frequent human infection.

Interestingly enough, all animals tested negative by PCR swab including those living in households with confirmed COVID-19 human infection and those with and without respiratory symptoms. This would appear to suggest that whilst pet animals can seroconvert, they may shed virus for relatively short periods of time. In a test of antibodies against the virus it was found that 3% of dogs and 4% of cats showed evidence of previous infection.

Interestingly enough, infection rates among the cats and dogs were comparable with those amongst the people in Europe at the time of testing.  This suggests that it is not unusual for pets to be infected. In households with known COVID-19 infection neutralising antibodies were detected in 6/47 dogs, that is 12.8% and 1/22 cats, that is 4.5%.

Dogs were significantly more likely to test positive for SARS-CoV-2 neutralising antibodies if they came from a known COVID-19 positive household. The link between the SARS-CoV-2 household infection and the pets’ seropositivity was only apparent for dogs, possibly suggesting greater interaction between positive people and their household dogs as compared with cats.

This contrasts with experimental studies where dogs were less susceptible to infection. In addition, a higher proportion of male dogs were seropositive compared to female dogs.  This compares with human COVID-19 infections with males at a higher risk of severe disease, however, in humans there does not appear to be any evidence for a difference in infection risk.  None of the young juvenile animals less than one year of age tested positive.

The suggestion that pet animals can seroconvert but shed virus for relatively short periods of time was found in experimental studies.  Cats stopped shedding virus by 10 days post infection and developed neutralising antibody responses by 14 days post infection.  Similar results were reported in experimental infection of dogs in which the virus was detected in faeces up to six days post-infection but not in oropharyngeal swabs. 

There would also appear to be a difference between species.  A naturally infected Pomeranian dog had SARS-CoV-2 RNA detected from nasal swabs by quantitative PCR for at least 13 days at low titre whilst the virus was not detected in faecal rectal samples. 

The authors concluded that companion animals living in areas of high human infection can become infected.  They observed seropositivity rates in animals compared to those of human via community sampling at a similar time in European contraries.  However, based on current knowledge, it appears unlikely that infected pets play an active role in SARS-CoV-2 transmission to humans. 

However, animal to human transmission may be more likely under certain environmental conditions such as the high animal population densities encountered on an infected mink farm.  The authors go on to finally conclude that when human transmission becomes rarer and contact tracing becomes more accessible, serological surveillance of pets may be advocated to develop a holistic picture of community disease dynamics and ensure that all transmission opportunities are terminated. 

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