While the origins of the coronavirus SARS-CoV-2 are still unclear, researchers have long suspected that the virus that causes COVID-19 originated in bats and might have found a host in another animal on its way to infecting humans.
This raises the question of which animal species can become infected with SARS-CoV-2, and, once infected, is it possible for them to transmit the disease back to humans while in close contact? A study conducted at the University of Georgia this summer aimed to answer these questions by examining whether common urban wildlife such as raccoons and skunks can be susceptible to SARS-CoV-2.
Based on the results, though, that possibility now seems remote.
In the study, researchers, led by professor Sonia Hernandez of the UGA Warnell School of Forestry and Natural Resources and the UGA College of Veterinary Medicine, inoculated raccoons and skunks with the novel coronavirus, then housed them alongside other virus-free raccoons and skunks. The experiment consisted of a control group where no animals were inoculated throughout the experiment, plus two treatment groups. One group was inoculated with a low dose and another with a high dose of the virus.
By the end of the eight-week study, raccoons did not show any signs of infection, nor did they shed virus during the experiment. On the other hand, two of the inoculated skunks did become infected and were actively shedding virus. But they never developed clinical disease, said Hernandez, and the amount of virus shed by the infected skunks was too low to infect the virus-free skunks placed in direct contact with them.
“Our study does not suggest that skunks are good reservoirs because only two got infected and shed virus,” said Hernandez. But given what we know about COVID-19’s beginnings, she added, understanding the potential for animal vectors is part of the overall picture of public health. “Knowing that this virus came from an animal reservoir, and knowing that millions of people in the United States have been infected, we thought it paramount that we determined if common and abundant North American free-living hosts could serve as reservoirs.”
This study is the first to investigate the susceptibility of raccoons and skunks to SARS-CoV-2. Researchers chose these animals based on their abundance in urban areas and the likeliness they may come into contact with humans—either indirectly, through consumption of trash, or directly, at wildlife rehabilitation centers.
Another reason to investigate skunks was to determine whether the general family of native mustelids—animals that include badgers, otters, ferrets, minks and others—are susceptible, as they are closely related to endangered species of mustelids, such as black-footed ferrets. Studies have demonstrated that mink and domestic ferrets are highly susceptible to the virus that causes COVID-19.
Recently, mink farms in Europe and the United States have experienced major outbreaks of SARS-CoV-2 infections, which has led to the culling of thousands of animals. Mink presumably first acquired the infection from sick caretakers, but then were able to transmit it to other mink and possibly back to humans.
The study included several faculty members from the UGA College of Veterinary Medicine as well as students. It was funded by a National Science Foundation RAPID grant.
While the study did not find strong evidence that raccoons and skunks can transmit SARS-CoV-2 to other animals, Hernandez said people can still work to reduce the probability of pathogen transmission between wildlife and humans by not leaving food outside for animals.
This practice creates opportunities for wildlife to come into contact with each other, with domestic pets and with humans, thus increasing chances of disease transmission. “There is a whole host of diseases that you can acquire if you leave food out, from distemper to salmonella,” she added.