Researchers Raise Concerns: COVID-19 Virus Undergoing Swift Evolution in White-Tailed Deer

 

Research Reveals Deer as Reservoirs of the Virus, Facilitating Continuous Mutations.

Fresh study outcomes indicate that white-tailed deer throughout Ohio have encountered the COVID-19 virus, and disconcertingly, the findings reveal that viral variations are evolving roughly three times quicker in deer compared to humans.

Researchers gathered 1,522 nasal swabs from deer roaming freely across 83 out of the state's 88 counties, spanning the period from November 2021 to March 2022. Over 10% of the samples exhibited positivity for the SARS-CoV-2 virus, and in at least 59% of the counties subjected to testing, at least one positive case was identified.

Genomic Analysis and Discoveries

Through genomic analysis, it was revealed that a minimum of 30 deer infections had been initiated by human transmission – a statistic that astonished the research team.

"We often consider interspecies transmission as an infrequent occurrence, yet this wasn't an extensive sample size, and we were able to confirm 30 instances of transmission. It appears that the virus is relatively adept at moving between humans and animals," stated Andrew Bowman, Associate Professor of Veterinary Preventive Medicine at The Ohio State University and co-senior author of the study.

He added, "Furthermore, the mounting evidence indicates that humans can contract the virus from deer – a development that isn't entirely unexpected. This transmission isn't likely to be unidirectional."

The cumulative findings imply that the white-tailed deer population serves as a reservoir for SARS-CoV-2, enabling a continuous process of mutation. The virus's presence within deer could potentially lead to its dissemination among other wildlife and livestock.

Published in the journal Nature Communications on August 28, 2023, the study sheds light on these insights.

Previous Observations and Expansion

Bowman and his colleagues had previously reported the identification of SARS-CoV-2 infections in white-tailed deer across nine locations in Ohio in December 2021. They have continued to monitor deer for infections by more recent variants.

"We expanded our investigation across Ohio to determine if this issue was confined to a specific area – and we discovered instances in various locations, indicating that this is not isolated to a particular region," Bowman stated. "Initial speculation was that urban deer might be more affected due to their proximity to humans. However, in rural parts of the state, we're identifying a considerable number of positive cases among deer."

Beyond identifying active infections, the research also revealed through blood samples containing antibodies, indicative of prior exposure to the virus, that an estimated 23.5% of Ohio's deer population had encountered the virus at some point.

Analysis of Variants

The collection of 80 whole-genome sequences from the samples showcased a diverse range of viral variants, including the highly transmissible delta variant, which was the dominant human strain in the United States during the early fall of 2021, comprising nearly 90% of the sequences. Additionally, the alpha variant, the first variant of concern identified in humans during the spring of 2021, was also detected.

Genetic analysis revealed that the composition of delta variants found in deer matched the prevalent lineages observed in humans at that time, indicating spillover events. Furthermore, clusters of deer-to-deer transmission were identified, spanning multiple counties.

Bowman noted, "There's likely a temporal aspect to our findings – our observations of a high prevalence of delta variants in deer align with the waning phase of the delta variant peak in humans. However, we had already moved past the detection of the alpha variant in humans. This raises concerns about the possibility that deer are harboring lineages that have vanished in the human population."

The study also suggested that COVID-19 vaccination is likely to offer protection against severe disease in the event of a spillover back to humans. An examination of the effects of deer variants on Siberian hamsters, an animal model used for SARS-CoV-2 studies, indicated that vaccinated hamsters experienced less severe illness compared to unvaccinated animals following infection.

Swift Evolution in Deer

Alarmingly, the viral variants circulating among deer are anticipated to continue evolving. Analysis of the mutations present in the samples provided compelling evidence of a notably accelerated evolution of both the alpha and delta variants in deer in comparison to their evolution in humans.

"Not only are deer becoming infected with and harboring SARS-CoV-2, but the pace of mutation is notably faster in deer, possibly leading the variants to diverge from those affecting humans," Bowman cautioned.

The exact manner in which the virus is transmitted from humans to white-tailed deer remains a mystery. Remarkably, despite the existence of approximately 30 million free-roaming deer in the U.S., significant outbreaks stemming from deer-origin strains have not transpired in humans.

Potential Implications

The likelihood of circulation among animals remains high. Bowman pointed out that roughly 70% of free-roaming deer in Ohio have not been exposed to or infected by the virus, suggesting a substantial population of susceptible animals that the virus could spread through with limited hindrance.

"The involvement of an animal host introduces factors that we must remain vigilant about," he explained. "If this trend persists for years and the virus becomes well-adapted to deer, could it pave the way for transmission to other animal hosts, whether wildlife or domesticated? This remains an unknown factor."

Martha Nelson from the National Library of Medicine served as the co-corresponding author of the study. Collaborators from Ohio State University including Dillon McBride, Steven Overend, Devra Huey, Amanda Williams, Seth Faith, and Jacqueline Nolting, along with researchers from institutions like St. Jude Children’s Research Hospital, the University of California, Los Angeles, the National Research Centre in Giza, Egypt, PathAI Diagnostics, Ohio Department of Natural Resources, U.S. Department of Agriculture, Columbus and Franklin County Metroparks, and the Rega Institute for Medical Research in Belgium also contributed to the study.

This research was supported by funding from the National Institute of Allergy and Infectious Diseases and Ohio State's Infectious Diseases Institute.