COVID-19: At-Risk Groups Identified

A genomics analysis of the ACE2 receptor reveals that many animal species are susceptible to SARS-CoV-2 infection. Humans are therefore far from being the only ones threatened by COVID-19.   Numerous cases of COVID-19 had already been documented in animals, including cats, dogs, ferrets, hamsters, lions, tigers, and mink. However, a new study rounds out the picture by offering a genomics and more concrete approach to potential animal reservoirs. The researchers focused on one of the virus’s entry points into human host cells: the ACE2 receptor (angiotensin-converting enzyme 2). ACE2 is present on many different types of cells in various tissues and, unsurprisingly, on the epithelial cells of the nose, mouth, and lungs. In humans, 25 amino acids of the receptor are involved in binding to SARS-CoV-2. This sequence of 25 amino acids therefore enables infection and can thus be used to predict it. By comparing this sequence—and the resulting molecular and structural properties—with those of other animals, researchers can predict their susceptibility to the virus. Animals with receptors that have a sequence with similar properties and that structurally match that of humans will, in principle, be at the highest risk of contracting SARS-CoV-2 via ACE2. Similarly, the more the amino acid sequence differs, the lower the risk. By conducting genomics analyses on the genomes of 410 vertebrate animals—including birds, fish, amphibians, reptiles, and 252 mammals, the researchers were able to identify which species have a receptor with sufficient affinity for the virus to allow its entry and are therefore susceptible to infection. Results: The species most susceptible to the coronavirus are often the most endangered species, according to the International Union for Conservation of Nature. Thus, 40% of the species classified as susceptible in the study are at risk of contracting SARS-CoV-2. These include several primate species—the western lowland gorilla, the Sumatran orangutan, and the northern white-cheeked gibbon. The study also found that certain marine mammals, such as gray whales and bottlenose dolphins, are at high risk. Domestic animals appear to be better protected. Cats, cattle, and sheep pose a moderate risk, while dogs, horses, and pigs pose a low risk of ACE2-mediated infection. Perhaps most surprising is that bats—despite having been the original reservoir of SARS-CoV-2—face only a very low risk of contracting the disease again via their ACE2 receptor. The current form of the virus could only have evolved through one or more intermediate hosts before infecting humans. While this information helps us better understand the pathogenic potential of COVID-19 in different animal species, it also enables us to better prevent the disease. Identifying potential hosts of SARS-CoV-2—and thus potential reservoirs—helps reduce the likelihood of future local outbreaks and resurgences. However, the study’s authors caution against overinterpreting the results and predictions presented here. These remain mere hypotheses until the infection has actually been identified in the species in question. This is a story to watch, then.