Prospective cohort; Ecological
Study population and setting
The study population included seven adult cats (1 male, 6 female, 5-8 years old) and three adult dogs (all female, 5-6 years old). Cats and dogs were housed in groups. Weight, body temperature, clinical status, and oral swabs were obtained prior to viral exposure, and all cats tested negative for feline enteric coronavirus antibody prior to starting the study. Cats were inoculated with 3×10^5 plaque forming units of SARS-CoV-2 and dogs received 1.4×10^5 plaque forming units intranasally. Three inoculated cats (cohort 1) were monitored for viral shedding via orapharyngeal swabs, nasal flushes, and blood samples between for 14 days post-inoculation. At 28 days post-inoculation, cats were re-challenged with 3×10^5 plaque forming units of virus, then oronasal samples were taken between for 14 days post re-challenge (up to 42 days after initial infection). Cats were euthanized at day 42 and tissues were collected for histopathology. Two cats (cohort 2) were exposed to the virus like cohort 1, then two naïve cats were introduced into the room with the infected cats 48 hours following initial infection. Inoculated cats were euthanized at day 5 post-inoculation, and tissues were collected for virus isolation and histopathology. Contact cats were euthanized at day 30 post-inoculation and necropsied. Dogs were sampled at the same frequency as cat cohort 1 for 42 days post-inoculation, but were not re-challenged with the virus.
Summary of Main Findings
None of the cats or dogs showed any clinical signs of infection, including fever or changes in body weight; the clearest pathological sign observed in cats was moderate rhinitis and minor interstitial pneumonia. All three cats in cohort 1 shed virus orally and nasally for up to five days post-inoculation. Contact cats from cohort 2 shed virus orally as early as 24 hours post-exposure. Cats in both cohort 1 and direct contact cats from cohort 2 developed antibodies to SARS-CoV-2 as early as 7 days post-inoculation that remained high until the end of the study. Re-challenged cats showed no signs of viral shedding during the 7 days following re-exposure, but did show a moderate increase in antibody titer. Viral shedding was not detected in any of the dogs post-infection, but dogs developed antibodies by day 14 post-exposure, although with lower titers than cats.
Compared to previous experimental studies of SARS-CoV-2 infection in cats, this study examines shedding kinetics over time, assesses virus neutralization, seroconversion, and transmission in the same experiment. This is also the first study to report protective immunity against SARS-CoV-2 following repeated exposure.
All animals were adults, so it is unclear whether the lack of observed clinical signs of infection changes with animal health status, age, and comorbidities. The study also does not investigate the potential for inter-species transmission, such as between cats and dogs, or between cats and humans.
The study confirms that cats are highly susceptible to SARS-CoV-2 infection in experimental conditions, and that they develop neutralizing antibodies that protect against subsequent challenge with the virus.