COVID-19 in cats : prevalence of antibodies in cats in Sweden, concern among owners and development of COVID-19 SIA as the analytical method

Abstract: COVID-19 is a disease which has had great impact on the world in 2020. It has infected millions of people during the year, and been confirmed in animals such as cats, dogs and minks. The receptor ACE2 which is the target for the virus SARS-CoV-2 to use for attachment to the cell, is very similar between cats and humans. Therefore, there is a risk for cats to become infected with SARS-CoV-2. Studies have shown that cats can be infected by aerosol transmission, can show symptoms and can develop antibodies. Prevalence of SARS-CoV-2 antibodies in cats have been investigated in Wuhan, by using ELISA showing that 14.7% (15/102) of sampled cats were positive. However, there are no studies done on seroprevalence in Sweden. The aim of this study was to investigate the prevalence of antibodies against SARS-CoV-2 in cats in four municipalities in Sweden. This by using a method previously not used for cats, but well tested for detection of SARS-CoV-2 antibodies in humans, called COVID-19 suspension immunoassay (SIA). The objective was to adapt the SIA to be able to detect antibodies against SARS-CoV-2 as well as against feline coronavirus (FCoV), which could have the capability to crossreact in the test. The goal was also to try and connect seroprevalence with different individual traits, environmental differences and whether the owner had been confirmed infected. The concern in cat owners regarding COVID-19 and their animals was to be simultaneously studied by a survey. Blood samples were collected from both sick and healthy cats in Uppsala, Östhammar, Tierp and Halmstad. They were categorized into two groups, with 56 samples in the first (A) and 147 in the other (B). In group A, the samples were attached to a survey in which the owner answered 15 questions about their animal, its home environment, closeness to humans and other animals and if the owner had been sick in COVID-19. In group B, serum samples were collected from the university hospital for animals in Uppsala (UDS) with no survey administered. Presence of SARS-CoV-2 antibodies in cat serum was analysed, using part of the spike protein (S1) as antigen. Six samples out of 203 turned out positive (preliminary cut off at >333 MFI), all in group B, which translates to a preliminary seropositivity of 3% in our population. Another two samples had doubtful results (MFI between 174-333), both in group A, why very little could be concluded from the survey regarding predisposing factors or symptoms. The two doubtfully positive cats did live very close to their humans, and one of the cats had a family with confirmed COVID-19. The COVID-19 SIA did unfortunately not work as well for FCoV despite efforts to try and solve a couple of possible reasons for failure, why it was not possible to examine the possibility for cross-reaction. However, previous studies have not shown any indications of this. In conclusion, this study indicates that cats can produce antibodies against SARS-CoV-2, and that the seropositivity was 3% in the population used for the study. The SIA is reliable for detection of antibodies against SARS-CoV-2 in human sera and seems to have potential for analysis in cat sera, but is not yet successfully adapted for FCoV. Owners concern for COVID-19 in cats was low. In the future, improvements and further studies could be done based on these results. A larger selection of cats, possibly from more areas of Sweden, should be included. All with information about their individual traits, environment, symptoms, closeness to humans and if they have been in contact with someone confirmed infected. A larger number of confirmed seronegative cats could aid in determining a more accurate cut off value for determining the results from the COVID-19 SIA. This study was performed in parallel with another study, by Frida Österberg, which investigated the same subjects as this one, but in dogs.