Study population and setting
The study population consisted of 9 domestic cats and 12 dogs (both from a broad age range) living with 18 owners in a veterinary community of 20 students in France (location not disclosed). Serum samples were collected from animals on March 25, 2020. The pets all had close contact with their owners including living in the same room, sharing the same bed, and/or licking their owners’ face or hands. Between February 25 and March 18, 2020, two of the 18 owners became infected with SARS-CoV-2 and tested positive for the virus, 11 of the other owners developed symptoms consistent with COVID-19 but were not tested, and the remaining 7 students in the community showed no symptoms of infection. An additional set of samples from 51 dogs and 7 cats collected from local animals before the epidemic between October 2015 and October 2018 was used for comparison in serological assays.
Summary of Main Findings
None of the 21 cats and dogs from the veterinary community showed any evidence of infection with SARS-CoV-2. Tests of an immune response to infection from blood samples (serology) and tests for viral genetic material (PCR) from nasal and rectal swabs collected from the animals for one week after the blood sampling on March 25 produced negative results for all animals. The additional 58 animals sampled before the epidemic also tested negative.
The community of veterinary students and their pets is especially useful because it is a closed population where no additional, potentially infected animals were entering the community. Assuming that pets within the community had limited contact with each other and other owners, cases of SARS-CoV-2 in infected animals could have been traced to their infected owners with which they had close contact. The additional nasal and anal swabs collected after March 25 are critical for confirming that the negative serological results were not due to a delayed immune response following viral infection (which would have been detected by PCR).
The authors do not know the viral load of the human COVID-19 patients, which if low, could have explained the lack of human to pet transmission. The limited number of animals tested cannot rule out that human-pet transmission of SARS-CoV-2 is possible, only that it is a rare event that may not be detectable in a small population of animals.
This is one of the first studies to investigate potential transmission of SARS-CoV-2 between infected humans and domestic animals with close contact between them.