September 17, 2020

expert reaction to unpublished conference abstract on pet cats and dogs, their owners, and SARS-CoV-2

A conference abstracted, presented at the European Society of Clinical Microbiology and Infectious Diseases Conference on Coronavirus Disease (ECCVID), discusses pet cats and dogs, their owners, and SARS-CoV-2.

Dr Dalan Bailey, Viral Glycoproteins Group Leader, The Pirbright Institute, said:

“This abstract presents a small case study that provides some evidence for SARS-CoV-2 infection of household pets, with the likely source of infection being their owners.  These conclusions are based on the presence of antibodies to the virus in the blood of these animals, with the highest incidence being in cats.  The development of an antibody response is likely the result of viral replication in these animals; however, the significance of these infections for the spread of COVID-19 remains unclear.  In almost all instances, swabs of the nose, throat and rectum of these animals did not identify viral RNA (with isolation of the virus itself not being attempted).  This is either because the animals were swabbed after the resolution of infection, or that the animals were not, at any time, shedding detectable amounts of virus.  Determining which of these possible explanations is true is very important as these data will help researchers to better understand the risk to pet owners and their pets.  In addition, confirming the isolation of virus from animals with the development of respiratory disease is also important.

“As this is only an abstract, the findings should be taken with caution until results are published in a peer reviewed journal.”

Prof Sally Cutler, Professor of Medical Microbiology, University of East London (UEL), said:

Is this robust research?

“I cannot judge the methods for robustness as details are lacking, but the concept was valid and findings concur with current knowledge.

Is there enough information available to be able to judge whether this is good science?

“As above, there is not enough on the methods.

Is this peer-reviewed, published work?

“All abstracts submitted would have been reviewed by an abstract committee (I reviewed about 30 for this meeting, but not this one), but this work is not a published paper.

Does the press release accurately reflect the research?

“Yes.

Is there evidence to show a ‘substantial proportion’ of cats and dogs are infected by their owners?

“This study has insufficient evidence to support this categorically (you would need to sequence the virus and perform SNP analysis), but would suggest this can occur.  We know cats are susceptible to infection, so in a shared home environment where there is infection, this is not surprising.  The infection being zoonotic (from animals) is by definition a multi-host pathogen.

They suggest people should isolate from their pets if they have SARS-CoV-2 – does the evidence justify that?

“Evidence of serious clinical symptoms in pets is lacking, though infection can occur.  Whether these infected pets can serve as a source for further human infection has not yet been demonstrated.  Pets can be a source of comfort for humans especially when unwell.  There is insufficient evidence to support isolation from pets at this point.

The author says “Transmission from pets to humans has not been reported, but since the virus changes minimally or not at all after transmission from humans to animals, such reverse transmission may occur” – is that supported by the evidence in this abstract?

“This has been shown for mink, but not for cats or dogs.  It is a theoretical though unproven risk, but there is no data to support this as a genuine concern.  Changes in the virus associated with passage through companion animals has not been reported.

How does this fit in with other evidence on pets and COVID-19?

“Cats have been previously published as susceptible to infection, but dogs are less susceptible.  Chickens and other species have also been assessed, but not susceptible.  There are various theories regarding why some other species might be susceptible such as core temperature, but none well researched to date.

Should pet owners worry?

“No.  If their pet is clinically unwell, they will need to seek veterinary advice and give fully background.  Pathology and viral replication has been described in cats more than dogs.  The latter can be infected (as supported by the seroconversion reported), but viral replication is very limited, so they are unlikely to be unwell as a consequence.

Any other comments?

“As SARS-CoV-2 has spilled over from an natural animal reservoir (bats?) the ability for it to infect other species beyond humans is not particularly surprising.  Some infectious agents are ‘multi-species’ whereas others are more host specific.”

Prof Tim Morris FRCVS, School of Veterinary Medicine and Science, University of Nottingham, said:

“Preliminary results made available at conferences before larger more detailed peer review studies are published and replicated are useful to stimulate discussion and further work, but at this stage are just that: preliminary results.  Constructive challenge should then begin as this abstract is presented, with questions including on how the antibody results compared with those taken before COVID-19 was first reported, if the antibody tests are specific to COVID and fully exclude other animal coronaviruses, and excluding other causes of respiratory infection in cats.

“As such these results should not be over-interpreted and so cause unwarranted alarm, particularly as currently there is no evidence reported of contagious SARS-CoV-2 transmission from pets to people¹.”

1 APHA Briefing Note 18/20 SARS-CoV-2 in Animals – Case Definition, Testing and International Reporting Obligations Date issued: 13 May 2020 – updated 27 July 2020 http://apha.defra.gov.uk/documents/ov/Briefing-Note-1820.pdf

Prof Alasdair Cook, School of Veterinary Medicine, University of Surrey, said:

“There are very few cases involved and this sample size makes the extrapolation to the wider population that “suggest a substantial proportion of pets in households of persons with COVID-19 seroconvert” difficult to justify, even with the “suggest” qualification.

“Further information on the sensitivity and specificity of the ELISA tests that were employed in dogs and cats would be valuable, bearing in mind that other non-COVID coronavirus infections are common.

“The respiratory disease is apparently only owner-reported and transient – there must be a substantial risk of observer bias, given the inevitable concern that COVID-confirmed people will have;  conceivably, any minor sniffle etc. might attract extra attention.

“Sero-conversion does not necessarily imply active infection and the PCR results suggest that viral excretion at the time of sampling is negligible or absent.

“Previous studies have shown that dogs and cats can be infected with COVID (e.g. Sit et al 2020 Nature; 2 of 15 dogs in Hong Kong shown infected; Sailleau et al Transboundary & Emerging Diseases – one cat from 22 sampled in France PCR positive).  Thus, this limited study simply confirms previous published reports.

“This study and others do not show transmission from pets to humans.  If transmission from pets to people was shown to be possible, it would be important to understand how important this pathway was compared to person to person transmission.  Currently, it is probable that the overwhelming means of transmission is person to person.  Within a COVID positive household, it is reasonable to suppose that direct person to person transmission will be more important than person-pet-person transmission.

“For households in lockdown or for vulnerable people who must self-isolate, the presence of a pet may have a very important beneficial impact on their mental health.  It would be extremely unfortunate if exaggerated or unjustified attention to this finding caused unnecessary concern to vulnerable pet owners or even potentially led some people to consider abandoning or otherwise re-homing their pets.

“Simple biosecurity and hygiene measures that should be employed anyway when managing a pet in a household, including regular handwashing and care of waste, would help to mitigate any threat.

“Notwithstanding the need to avoid causing alarm amongst pet owners, further epidemiological studies to investigate any association between pet ownership and risk of human COVID infection would be useful.”

The abstract ‘Surveillance of pets in households of persons with COVID-19 for SARS-CoV-2 infection’ by D. Bienzle et al. has been press released from the European Society of Clinical Microbiology and Infectious Diseases Conference on Coronavirus Disease (ECCVID). 

There is no paper and this is not peer-reviewed.

Declared interests

Prof Tim Morris: “Member of Defra’s Animal Helath and Welfare Board for England.”

None others received.