U.S. scientists have found widespread asymptomatic COVID infections in white-tailed deer, heightening concerns about the ability of the novel virus to mutate in multiple animal hosts and spill back into humans causing new pandemics.
“In principle, SARS-CoV-2 infection of an animal host could result in it becoming a reservoir that drives the emergence of new variants with risk of spillback to humans,” said the scientists in a new paper.
Suresh Kuchipudi, Huck Chair in Emerging Infectious Diseases at the Pennsylvania State University and lead author of the study noted in a press release that the findings highlight “that many urgent steps are needed to monitor the spread of the virus in deer and prevent spillback to humans.”
Researchers examined lymph gland samples taken from 151 free living and 132 captive deer in southeastern Iowa during the hunting season and found one-third had evidence of COVID infection between September 2020 and January 2021.
When the scientists sequenced the genomes from COVID positive samples, they found that their lineages directly corresponded to strains peaking in Iowa residents at the same time, causing around 900 cases a day.
Although COVID has been found in domestic pets and zoo animals and farmed carnivores such as mink, the Iowa study is the first to show “widespread dissemination of SARS-CoV-2 into any free-living species.”
The study is not yet submitted to a peer-reviewed journal. It is so far posted on the pre-print server bioRxiv.
White-tailed deer, which number in the tens of millions, can be found in almost every Canadian province, throughout the United States and in parts of South America.
Of all of North America’s large mammals, the white-tailed deer is the most widely distributed.
The infection likely spread from humans to deer and then from deer to deer with multiple spillovers, scientists posit. Iowa has many deer farms where contact with humans is common.
The discovery is cause for concern for a number of reasons. In humans, the virus has already shown a marked capacity to mutate. Variants such as Delta are already more infectious and deadly than the original Wuhan strain.
Mutants have already emerged in Europe where COVID swept through mink farms in the Netherlands and Denmark, resulting in the killing of millions of caged animals raised for fur.
Infections passed between infected mink handlers and then back from infected mink to humans.
Because animals host a variety of coronaviruses, COVID could combine with these relatives, “opening potential avenues for the acquisition of genes that might serve to increase” the virus’s ability to evade immune detection and become more infectious, the paper says.
Wild animal reservoirs are not affected by human vaccination campaigns and “thus represent a looming threat of re-emergence into humans,” says the study.
Scientists couldn’t determine if COVID infections were more prevalent in wild deer than in farmed deer or deer raised on preserves for hunting, because four times as many lymph samples were taken from wild deer.
“Our results suggest that deer have the potential to emerge as a major reservoir host for SARS-CoV-2, a finding that has important implications for the virus's genomic diversity and future trajectory of the pandemic,” concludes the study.
The current pandemic is assumed to have begun when the SARS-CoV-2 novel virus spilled over from wild bats into another as yet unidentified mammal species or directly into humans sometime in the fall of 2019 in Wuhan City where three separate laboratories house the largest collection of bat coronaviruses in the world.
Since then, the scientists have learned the virus can infect a variety of animals including ferrets, cats, rabbits, dogs, tree shrews, hamsters and non-human primates such as macaques. And that infected cats, tree shrews, hamsters and ferrets can spread the virus to people.
But the mustelid family of animals seems particularly susceptible to the virus and vulnerable to viral spillover. These carnivores include ferrets, badgers, raccoons, raccoon dogs, otters, martens, wolverines, mink and nearly 50 other species.
Scientists already fear that SARS-CoV-2 has spilled into wild mustelids, which could serve as another permanent reservoir of infection for other animal species.
Attempts at infecting pigs and several poultry species with SARS-CoV-2 have so far proven unsuccessful. Experimentally infected deer readily transmit the virus to other susceptible white-tailed deer.
The coronavirus SARS-CoV-2 that causes COVID can evolve a million times faster than human genes or fruit fly genes.