Coronaviruses and animals: what are the risks of contamination and transmission COVID-19 with respect to species?
Text updated on 2020-09-02
Some animal species, both domestic and wild, are more at risk than others of contracting the SARS-CoV-2 coronavirus responsible for COVID-19. Experimental data and natural conditions now make it possible to establish a risk scale for about fifteen species.
At the beginning of the COVID-19 outbreak, the Chinese authorities stressed the risks of human contamination by wild animals, indicating that the first patients with the disease COVID-19 were observed around the animal market in Wuhan. Other countries such as France focused on the risks of human-to-human contamination. What do we know today about the animal-to-human transmission of the SARS-CoV-2 coronavirus, with a few months of hindsight?
Under experimental laboratory conditions, it has been shown that the SARS-CoV-2 coronavirus collected from humans cannot infect pigs, chickens or ducks but can infect cats, dogs, hamsters, ferrets, tree shrews, bats and non-human primates and be detected in their respiratory tracts. Mild to moderate symptoms have been observed in only some of these species: rhesus monkeys, cats, tigers and hamsters. Only hamsters showed severe clinical symptoms. In addition, infected hamsters, cats and ferrets transmitted the coronavirus to other hamsters, cats and ferrets. Apart from these experimental infections, a few cats and dogs belonging to infected individuals tested positive for the SARS-CoV-2 coronavirus, and a few infected cats showed mild respiratory symptoms. On two mink farms in the Netherlands, workers independently infected mink, then the coronavirus spread within the mink farms and one employee probably contracted COVID-19 from the minks.
For other species, we do not yet have experimental data. However, it is possible to assess the risk of SARS-CoV-2 coronavirus infecting a given species by analyzing the ACE2 receptor present on the surface of its cells. For SARS-CoV-2 coronavirus to be infectious, it must enter the cells of its host after recognizing part of the ACE2 protein, which acts as a lock for the coronavirus key. For a given animal species, it can be considered by approximation that the closer this part of ACE2 (the lock) is to that of humans, the greater the likelihood of being infected with the SARS-CoV-2 coronavirus. On the other hand, it is not possible to predict the susceptibility of a species to SARS-CoV-2 coronavirus solely based on its phylogenetic proximity to humans because some mutations of ACE2 have occurred in several species over the course of evolution.
Risk of contamination in each species : ranging from 0 (no risk) to 3 (high risk)
mink: 3 (human-to-mink and mink-to-human contamination observed)
cats: 2 (some infections observed in the laboratory and under natural conditions, no cat-to-human transmission reported, cat-to-cat transmission possible)
tigers: 2 (some infections observed under natural conditions, no tiger-to-human transmission reported)
dogs: 1 (rare infections observed in the laboratory and under natural conditions, no dog-to-human transmission reported)
tree shrews: 1 (mild infection observed in the laboratory)
guinea pigs: 0-1 (no experimental study, their ACE2 receptor should not be well recognized by the SARS-CoV-2 coronavirus)
rabbits: 0-1 (no experimental study, their ACE2 receptor should not be well recognized by the SARS-CoV-2 coronavirus)
rats: 0-1 (their ACE2 receptor should not be recognized by the SARS-CoV-2 coronavirus, no experimental study)
ducks: 0 (no laboratory infection)
Pigs, wild boars: 0 (in the laboratory no infection was observed even though their ACE2 receptor is similar to human)
hens, chickens: 0 (no laboratory infection)
mice: 0 (no laboratory infection, ACE2 receptors not recognized by SARS-CoV-2 coronavirus)
The SARS-CoV-2 coronavirus was inoculated into the noses of 6 ferrets, 7 cats, 5 dogs, 5 pigs, 5 chickens and 5 ducks. The pigs, chickens and ducks were not contaminated. However, the ferrets, cats, and 2 of the 5 dogs were contaminated. Young cats (70-100 days) appear to be more susceptible than older cats (6-9 months). Out of 6 healthy cats, only one of them was infected after having been in contact with a contaminated cat. The 2 dogs brought in contact with the contaminated dogs were not infected.Shi, J., Wen, Z., Zhong, G., Yang, H., Wang, C., Huang, B., ... & Zhao, Y. (2020). Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS-coronavirus 2. Science, 368(6494), 1016-1020.
The SARS-CoV-2 coronavirus was inoculated into the noses of 9 bats (Rousettus aegyptiacus), 9 ferrets (Mustela putorius), 9 pigs (Sus scrofa domesticus) and 17 chickens (Gallus gallus domesticus). The chickens and pigs were not infected. All bats were infected: the coronavirus was detected several days later but no clinical signs, fever, weight loss or mortality were observed. Of 3 new healthy bats added to the cage, one was contaminated by the infected bats. The ferrets were all infected and passed it on to the other three healthy ferrets added to their cages without showing any signs of disease. The ferrets and bats developed an immune response to the SARS-CoV-2 infection with neutralizing antibodies.Schlottau, K., Rissmann, M., Graaf, A., Schön, J., Sehl, J., Wylezich, C., ... & Grund, C. (2020). SARS-CoV-2 in fruit bats, ferrets, pigs, and chickens: an experimental transmission study. The Lancet Microbe.
Ferrets are highly susceptible to infection with the SARS-CoV-2 coronavirus and can transmit the virus by direct or indirect contact through a grid.Kim, Y.I., Kim, S.G., Kim, S.M., Kim, E.H., Park, S.J., Yu, K.M., ... & Um, J. (2020). Infection and rapid transmission of SARS-CoV-2 in ferrets. Cell host & microbe.
The hamster has an ACE2 receptor that should be well recognized by the SARS-CoV-2 coronavirus based on computer predictions. In the laboratory, hamsters are infected with the SARS-CoV-2 coronavirus and develop pulmonary symptoms. In five cages, an infected hamster was matched with a healthy hamster and in each case the healthy hamster was infected. Pigs and rabbits also possess an ACE2 receptor that should be recognized by the SARS-CoV-2 coronavirus based on computer predictions.Chan, J. F. W., Zhang, A. J., Yuan, S., Poon, V. K. M., Chan, C. C. S., Lee, A. C. Y., ... & Liang, R. (2020). Simulation of the clinical and pathological manifestations of Coronavirus Disease 2019 (COVID-19) in golden Syrian hamster model: implications for disease pathogenesis and transmissibility. Clinical Infectious Diseases.
Hamsters can be infected with the SARS-CoV-2 coronavirus and can transmit it to other hamsters through direct contact or by aerosolization. They lose weight, develop an immune response to SARS-CoV-2 infection with neutralizing antibodies and eventually regain their original weight.Sia, S. F., Yan, L. M., Chin, A. W., Fung, K., Choy, K. T., Wong, A. Y., ... & Peiris, M. (2020). Pathogenesis and transmission of SARS-CoV-2 in golden hamsters. Nature, 1-7.
Cats can be infected in the laboratory with the SARS-CoV-2 coronavirus and are capable of transmitting it through direct contact to other cats. Cats infected in the laboratory did not develop symptoms but showed a strong immune response to the SARS-CoV-2 infection in terms of neutralising antibodies, which should prevent a second reinfection. No SARS-CoV-2 virus particles were detected in dogs previously infected with SARS-CoV-2 coronavirus but an immune response with the production of neutralizing antibodies was observed.Bosco-Lauth, A., Hartwig, A. E., Porter, S., Gordy, P., Nehring, M., Byas, A., ... & Bowen, R. (2020). Pathogenesis, transmission and response to re-exposure of SARS-CoV-2 in domestic cats. bioRxiv.
In outbreaks where human COVID-19 cases were confirmed in Hong Kong, 2 of the 15 dogs tested were positive for SARS-CoV-2 coronavirus. An immune response with neutralizing antibodies was detected in these 2 dogs. The genetic sequences of the viruses in the 2 dogs were identical to those of the viruses detected in the corresponding humans, confirming that these are indeed cases of human-to-animal transmission. The animals remained asymptomatic during the quarantine.Sit, T. H., Brackman, C. J., Ip, S. M., Tam, K. W., Law, P. Y., To, E. M., ... & Perera, R. A. P. M. (2020). Infection of dogs with SARS-CoV-2. Nature, 1-6.
Mink in 11 farms in the Netherlands were found to carry the SARS-CoV-2 coronavirus. The minks showed respiratory and gastrointestinal signs, and the number of deaths in the minks increased. As some workers on these farms were showing COVID-19 symptoms a few days earlier, it is likely that farm workers were responsible for the mink infections. Some cats in the surrounding area also developed antibodies to the coronavirus, suggesting that they were infected with mink.Oreshkova, N., Molenaar, R. J., Vreman, S., Harders, F., Munnink, B. B. O., Hakze-van der Honing, R. W., ... & Tacken, M. G. (2020). SARS-CoV-2 Infection in farmed minks, the Netherlands, April and May 2020. Eurosurveillance, 25(23), 2001005.
Macaques infected with SARS-CoV-2 through combined intranasal and intratracheal administration excreted coronavirus in the upper and lower respiratory tracts but exhibited mild clinical symptoms.Rockx, B., Feldmann, F., Brining, D., Gardner, D., LaCasse, R., Kercher, L., ... & Porcella, S. F. (2011). Comparative pathogenesis of three human and zoonotic SARS-CoV strains in cynomolgus macaques. PLoS One, 6(4), e18558.
Infection of tree shrews in the laboratory.Zhao, Y., Wang, J., Kuang, D., Xu, J., Yang, M., Ma, C., ... & Gao, J. (2020). Susceptibility of tree shrew to SARS-CoV-2 infection. bioRxiv.
Mice infected in the laboratory with SARS-CoV-2 coronavirus showed no symptoms and no viral load, while transgenic mice with the human ACE2 receptor became infected, developped pneumonia and lose weight.Bao, L., Deng, W., Huang, B., Gao, H., Liu, J., Ren, L., ... & Qu, Y. (2020). The pathogenicity of SARS-CoV-2 in hACE2 transgenic mice. BioRxiv.
At a New York zoo, five tigers and three lions tested positive for SARS-CoV-2. These animals were infected by an asymptomatic zoo staff member who was infected with COVID-19.Article Newsroom.
By analyzing the amino acid sequences that make up the ACE2 lock in various species and modeling their physical interactions with the Spike key of the SARS-CoV-2 coronavirus, it can be inferred that the SARS-CoV-2 coronavirus is unlikely to infect rats, mice, guinea pigs and rabbits. On the other hand, the Spike key seems to recognize the ACE2 lock in ferrets and cats as well as in humans. The other lock used by the SARS-CoV-2 coronavirus to enter cells, part of the TMPRSS2 protein, is identical in all species tested in this study, and therefore does not explain the differences in coronavirus susceptibility observed between species.Brooke, G. N., & Prischi, F. (2020). Structural and functional modelling of SARS-CoV-2 entry in animal models. Research Square preprint.
Analysis of contamination cases in 16 mink farms in the Netherlands. Analysis of the SARS-CoV-2 coronavirus sequences collected from mink and humans indicates that there have been at least 10 cases of mink to human transmission.Munnink et al (2020) Jumping back and forth: anthropozoonotic and zoonotic transmission of SARS-CoV-2 on mink farms. BioRxiv.