Study population and setting
The focal population included 817 pets (540 dogs, 277 cats) in northern Italy surveyed from March to May 2020. Samples mainly came from the region of Lombardy (476 dogs, 187 cats). Oropharyngeal, nasal, and rectal swabs were collected by their regular veterinarian during routine visits. Pets were from households with and without COVID-19 cases. A subset of animals (340 dogs, 188 cats) had full clinical histories available, including breed, sex, age, exposure to COVID-19 cases, and presence of respiratory symptoms. Another subset of animals had serum samples available to test for SARS-CoV-2 antibodies: 188 dogs and 63 cats with full histories and 200 dogs and 89 without historical information.
Summary of Main Findings
None of the 839 swab samples from 817 animals tested positive for SARS-CoV-2 based on a PCR test targeting the nucleoprotein and envelope protein genes; this includes 38 dogs and 38 cats with respiratory symptoms at the time of sampling, and 64 dogs and 57 cats that were living in homes with confirmed COVID-19 cases. Serological testing showed that 13/388 dogs (3.4%) and 6/152 cats (3.9%) had neutralizing antibodies to SARS-CoV-2. Dogs from households with COVID-19 cases and male dogs were significantly more likely to be seropositive. There was also a borderline positive (p = 0.051) rank correlation between the seropositivity of dogs and the human COVID-19 case density (cases per 10,000 people) in provinces with at least ten samples. Similar trends were observed in cats, but statistical tests were not significant.
The study included a much larger sample size of cats than a previous serological survey in China, and was the first large survey of SARS-CoV-2 infection and serology in dogs. Animals came from a range of age groups and varied in their exposure to human COVID-19 cases, unlike other reports that tested animals from COVID-19 case households only.
It is unclear where and when many animals were exposed to SARS-CoV-2, since some were not from households with COVID-19 cases. The small sample size meant that the study was not powered to detect differences in prevalence between animals from COVID-19 case households and non-case households or differences between male and female cats. The correlation between animal seropositivity and human COVID-19 case density across provinces should be regarded with caution because of the very limited number of provinces with sufficient data (n = 4 for cats, n = 6 for dogs).
This study adds to evidence in China and the United States that dogs and cats produce antibody responses following exposure to SARS-CoV-2 from their owners or within the community. However, research has yet to provide evidence that pets with SARS-CoV-2 infection can transmit the virus back to humans. Additionally, studies have not provided evidence of transmission between cats or dogs outside of the laboratory.
This review was posted on: 10 August 2020