Current Status of Putative Animal Sources of SARS-CoV-2 Infection in Humans: Wildlife, Domestic Animals and Pets

Abstract

SARS-CoV-2 is currently considered to have emerged from a bat coronavirus reservoir. However, the real natural cycle of this virus remains to be elucidated. Moreover, the COVID-19 pandemic has led to novel opportunities for SARS-CoV-2 transmission between humans and susceptible animal species. In silico and in vitro evaluation of the interactions between the SARS-CoV-2 spike protein and eucaryotic angiotensin-converting enzyme 2 (ACE2) receptor have tentatively predicted susceptibility to SARS-CoV-2 infection of several animal species. Although useful, these data do not always correlate with in vivo data obtained in experimental models or during natural infections. Other host biological properties may intervene such as the body temperature, level of receptor expression, co-receptor, restriction factors, and genetic background. The spread of SARS-CoV-2 also depends on the extent and duration of viral shedding in the infected host as well as population density and behaviour (group living and grooming). Overall, current data indicate that the most at-risk interactions between humans and animals for COVID-19 infection are those involving certain mustelids (such as minks and ferrets), rodents (such as hamsters), lagomorphs (especially rabbits), and felines (including cats). Therefore, special attention should be paid to the risk of SARS-CoV-2 infection associated with pets.

Keywords: COVID-19; SARS-CoV-2; animal reservoirs; companion animals; domestic animals; modes of transmission; pets; wild animals; zoonosis.

Figure 1

SARS-CoV-2 zoonotic risk associated with exposure to pets. The susceptibility of pets to SARS-CoV-2 infection, and therefore the potential risk of transmission of this virus from these animals to humans, can be evaluated as nul or low (green animals), medium (yellow) or high (red). The arrows and numbers indicate the currently demonstrated transmission chain of SARS-CoV-2: (1) from human-to-human; (2) from animal-to-animal within a specific animal species (cats, hamsters, and ferrets); and (3) from human-to-animal (cats and ferrets).

Figure 2

Epidemiological schema of SARS-CoV-2 virus emergence from bat coronaviruses. This figure represents an hypothesis of SARS-CoV-2 emergence and spread, including the following steps: (1) the circulation of coronaviruses in bats, which are animals with spatial aggregation and grooming behavior, can lead to the emergence of new viral genotypes (including SARS-CoV-2, red star) via mutations and recombinations; (2) a given animal species (e.g., a bat predator such as the kolonok) might be infected by SARS-CoV-2, whereas (3) other animals (e.g., mice and rats) remain unsusceptible to infection by any of the new genotypes (unadapted hosts); (4) the SARS-CoV-2 infected animal species may transmit this virus to humans through direct contact or indirectly (e.g., via the consumption of contaminated food products), or (5) after amplification of the virus in other animal hosts; (6) infected humans may transmit the new coronavirus to susceptible farm animals (e.g., the minks) and pets, themselves becoming potential sources of human infections.