Zooanthroponotic transmission of SARS-CoV-2 and host-specific viral mutations revealed by genome-wide phylogenetic analysis
Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a generalist virus, infecting and evolving in numerous mammals, including captive and companion animals, free-ranging wildlife, and humans. Transmission among non-human species poses a risk for the establishment of SARS-CoV-2 reservoirs, makes eradication difficult, and provides the virus with opportunities for new evolutionary trajectories, including selection of adaptive mutations and emergence of new variant lineages. Here we use publicly available viral genome sequences and phylogenetic analysis to systematically investigate transmission of SARS-CoV-2 between human and non-human species and to identify mutations associated with each species. We found the highest frequency of animal-to-human transmission from mink, compared with lower transmission from other sampled species (cat, dog, and deer). Although inferred transmission events could be limited by sampling biases, our results provide a useful baseline for further studies. Using genome-wide association studies, no single nucleotide variants (SNVs) were significantly associated with cats and dogs, potentially due to small sample sizes. However, we identified three SNVs statistically associated with mink and 26 with deer. Of these SNVs, [~][2/3] were plausibly introduced into these animal species from local human populations, while the remaining [~][1/3] were more likely derived in animal populations and are thus top candidates for experimental studies of species-specific adaptation. Together, our results highlight the importance of studying animal-associated SARS-CoV-2 mutations to assess their potential impact on human and animal health. ImportanceSARS-CoV-2, the causative agent of COVID-19, can infect many animal species, making eradication difficult because it can be reseeded from different reservoirs. When viruses replicate in different species, they may be faced with different evolutionary pressures and acquire new mutations, with unknown consequences for transmission and virulence in humans. Here we analyzed SARS-CoV-2 genome sequences from cats, dogs, deer, and mink to estimate transmission between each of these species and humans. We found several transmission events from humans to each animal, but relatively few detectable transmissions from animals back to humans, with the exception of mink. We also identified three mutations more likely to be found in mink than humans, and 26 in deer. These mutations could help the virus adapt to life in these different species. Ongoing surveillance of SARS-CoV-2 from animals will be important to understand their potential impacts on both human and animal health.