Seroprevalence of SARS-CoV-2 in dogs in the city of Zagreb and Zagreb County

SARS-CoV-2 is a novel coronavirus that has spread among the human population at the end of 2019. It has been reported over 130 million outbreaks and around 3 million deaths worldwide so far. An animal origin of this coronavirus is generally accepted in the scientific community, and it brings the question about the epidemiological role of animals in COVID-19. SARS-CoV-2 infections in dogs have been described, and their susceptibility to infection has also been proven in experimental infections. Dogs as pet animals have a potentially significant role in the epidemiology of COVID-19 due to their close contact with owners. From July 1st to December 31st 2020, 1069 remaining dog sera samples from the city of Zagreb and Zagreb County were collected. Additionally, collected data included signalment, medical history and clinical signs. Serum samples were tested by enzyme- linked immunosorbent assay (ELISA), which was developed and validated for this study. For the statistical analysis of results, a chi-squared test was used. Of the total number of dogs tested, SARS-CoV-2 antibodies were confirmed by an ELISA test in 14.69%. The highest number of positive samples was in September and December 2020. There was gender predisposition with significantly increased seroprevalence in male dogs (p=0, 007). Unlike in the human population, age predisposition has not been proven (p=0.2). Breed predisposition was also pronounced (p=0.01). Belgian Shepherds were significantly more likely to be infected than any other dog breeds. The serological status of dogs could not be related to the occurrence of respiratory or gastrointestinal clinical signs (p = 0.37). There was no relation between the SARS- CoV-2 status of dogs and the reason for the veterinary visit. Dogs from shelters were not at higher risk of SARS-CoV-2 infection than private- owned ones (p = 0.96). This study shows that SARS- CoV-2 has become a significant pathogen among the dog population. At the end of the pandemic's first wave, the seroprevalence in Croatia was 7.45% and now is two times higher. Although it has not been proven that dogs have a significant role in the epidemiology of infection in humans, there is a question of the possible impact of SARS-CoV-2 on animal health.