While COVID-19 variants Alpha, Gamma and Delta are no longer circulating among humans, they continue to spread in white-tailed deer.
The animals are the most abundant large mammal in North America. Scientists aren't sure whether the deer could act as long-term reservoirs for these obsolete variants.
In a new study, researchers at Cornell University, in Ithaca, N.Y., collected 5,700 deer lymph node samples from 2020 to 2022 in the state, comparing the genomic sequences of the variants found in deer with sequences of the same variants taken from humans across New York.
The investigators found the viruses had mutated in the deer, which suggested the variants had likely been circulating in the animals for many months.
“One of the most striking findings of this study was the detection of co-circulation of three variants of concern — Alpha, Gamma and Delta — in this wild animal population,” Diego Diel, an associate professor of population medicine and diagnostic sciences at Cornell, said in a university news release.
When the researchers detected the Alpha and Gamma variants in the deer, there was no evidence of these viral strains still circulating in humans and they hadn't been for four to six months.
“When we did sequence comparisons between those viruses recovered from white-tailed deer with the human sequences, we observed a significant number of mutations across the virus genome,” Diel said.
Some of the viruses had up to 80 mutations compared with the human sequences. This provided further evidence that the viruses had likely been circulating in the deer for some time. The virus may have adapted to deer, possibly making it more transmissible among them.
Deer have been infected with COVID-19 through ongoing contact with humans, possibly from hunting, wildlife rehabilitation, feeding of wild animals or through wastewater or water sources, according to the study.
“A virus that emerged in humans in Asia, most likely after a spillover event from an animal reservoir into humans, apparently, or potentially, has now found a new wildlife reservoir in North America,” Diel said.
A 2022 study by Diel and others revealed that across five states surveyed in 2021, the COVID-19 virus was found in up to 40% of white-tailed deer. There are 30 million of the animals in the United States.
The researchers said more study is needed to confirm whether these variants will disappear in deer over time or spread to other wildlife, such as predators.
“Because of the evidence obtained in our study, it is very important to continue to monitor the virus in these animal populations to really understand and track changes that could lead [to] or favor spill back into humans and other wildlife,” Diel said.
The study findings were published Jan. 31 in the Proceedings of the National Academy of Sciences.
The U.S. Centers for Disease Control and Prevention has more on COVID-19 in animals.
SOURCE: Cornell University, news release, Jan. 31, 2023