A study published by Hamer and others published 19th May 2021 researched this issue.  

They argue that understanding the ecological and epidemiological role of pets in the transmission of SARS-CoV-2 is critical for animal and human health and helps to identify household reservoirs and predicts the potential enzootic maintenance of the virus. 

They conducted a longitudinal household transmission study of 76 dogs and cats living with at least one SARS-CoV-2 infected human in Texas and found that 17 pets from 25.6% of 39 households met the definition for SARS-CoV-2 infection in animals.  

This included:

  • 3/17- 17.6% cats
  • 1/59- 1.7% dogs 

That were positive by PCR testing.  

The virus was successfully isolated from the respiratory swabs of one cat and one dog.  

They found that whole genome sequencing of the SARS-CoV-2 obtained from the four positive animals were unique variants grouped with genomes circulating amongst the population with COVID-19 in Texas. 

Re-sampling showed persistence of viral RNA for at least 25 days post initial test. 

Additionally, they found:

  • 7/16- 43.8% cats 
  • 7/59-11.9% dogs 

harboured SARS-CoV-2 neutralising antibodies upon initial sampling, with relatively stable or increasing titres over the two to three months of follow up and no evidence of sero-reversion.  

The majority 82.4% of infected pets were asymptomatic.  

Interestingly, of the 17 animals that were PCR positive, only three animals were reported to have mild signs of the disease including three days of sneezing in the PCR positive cat; lethargy in a PCR positive cat and sneezing in an antibody positive dog.  

On re-sampling these and all other animals in the study were reported to be in good health.  

Based on literature reports, only slightly less than half of all animals reported with SARS-CoV-2 infection had clinical signs, which may include: 

  • Fever 
  • Coughing 
  • Difficulty breathing  
  • Shortness of breath
  • Lethargy 
  • Sneezing
  • Nasal discharge 
  • Ocular discharge
  • Vomiting and diarrhoea.  

This study revealed a much higher proportion of asymptomatic animals suggesting that infected companion animals showing no clinical signs or only mild, transient illness may be more numerous than global reporting currently captures.  

They concluded that reverse zoonotic transmission of SARS-CoV-2 from infected people to animals may occur more frequently than recognised.

Dr Paul Ettlinger

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