SARS-CoV-2 infection in companion animals: An updated mini-review of susceptibility, transmission and one health significance

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), can infect a broad range of mammalian species, including companion animals. Early reports during 2020 established that cats and dogs can acquire SARS-CoV-2, particularly after close contact with infected people. However, the evidence available at that time was limited and was largely based on individual case reports and experimental studies. Since then, a substantial body of epidemiological, serological, experimental, and genomic evidence has accumulated. This mini-review summarizes the current evidence concerning SARS-CoV-2 infection in cats and dogs, with particular emphasis on experimental susceptibility, natural infection, human-to-animal transmission, animal-to-animal transmission, and animal-to-human transmission. Current evidence indicates that human-to-pet transmission is the predominant documented direction of transmission in household settings. Natural infection in general companion-animal populations is generally uncommon, whereas infection and seropositivity are substantially higher among animals living with SARS-CoV-2-infected people. Cats appear to be more susceptible than dogs in several experimental and epidemiological studies, although susceptibility may vary according to viral variant, exposure intensity, study design, and diagnostic method. Clinical disease in naturally infected companion animals is generally absent or mild, with respiratory and gastrointestinal signs reported in some animals. Evidence for pet-to-human transmission is considerably weaker than evidence for human-to-pet transmission, although a suspected cat-to-human transmission event has been investigated using epidemiological and genomic evidence. The epidemiological importance of companion animals should also be considered in comparison with other animal hosts. Farmed mink have demonstrated extensive animal-to-animal transmission and documented spillback to humans, whereas white-tailed deer have demonstrated repeated human-to-deer introductions and subsequent deer-to-deer transmission. Overall, available evidence does not support household cats and dogs as major reservoirs or drivers of human COVID-19 transmission. Nevertheless, they remain important susceptible hosts at the human-animal interface and may serve as useful sentinels for viral circulation. Continued targeted surveillance and genomic monitoring are therefore warranted within a One Health framework.