Researchers assessed six cases reported between 2020 and 2023 and sampled wild animals from six sites in Alaska.
An investigation of borealpox cases in Alaska determined that the virus is likely being spread from small mammals like voles and shrews to people, researchers said.
Borealpox virus — formerly called Alaskapox — was first identified in Fairbanks, Alaska, in 2015. It is one of several orthopoxviruses that have emerged or resurged amid waning global immunity to smallpox, a result of discontinued vaccination campaigns against that eradicated disease.
According to CDC epidemiologist Eric Q. Mooring, ScD, SM, MPhil, the current investigation was prompted by the identification of a case of borealpox in 2020.
“This was only the second time that the virus had ever been identified and we wanted to learn as much as we could about it,” Mooring told Healio.
He explained that orthopoxviruses typically circulate in wildlife but can also spread from person-to-person.
Mooring and colleagues investigated if borealpox virus was present in small mammals in Alaska or if there was evidence of person-to-person transmission. They interviewed six people with confirmed cases to gather travel history and potential exposures. The patients included:
A seventh case of borealpox was reported in December 2023, but that patient died the following January — the first death from borealpox — and was not included in this study.
The researchers interviewed the remaining adult patients and the mother of the young girl to collect information on travel history, daily activities and exposure to animals in the 4 weeks before their symptoms began. The interviews revealed that five of the six patients had similar clinical illness, and that none had traveled outside of Alaska during the timeframe in question, although three of the patients traveled to other parts of Alaska.
The investigation did not turn up any evidence of person-to-person transmission, Mooring noted.
The researchers also trapped small mammals — including voles, shrews, flying squirrels, red squirrels and a porcupine — for sampling and orthopoxvirus testing. They also tested companion animals of some patients.
Overall, testing detected viral DNA in 13 animals, with identical viral isolates collected from voles and shrews, which the authors wrote “might indicate a linkage between species.”
“We found the strongest evidence [of borealpox virus] in northern red-backed voles. This species is prolific and ubiquitous in Alaska,” the researchers wrote.
Genetic distance and phylogenetic analyses indicated that there were multiple spillover events from animals to humans. Mooring and colleagues noted three ways this might occur:
Based on these findings, Mooring and colleagues concluded that borealpox is a zoonotic disease in Alaska.
“While borealpox has only been identified in Alaska, the small mammal species in which we found evidence of the virus have broad geographic distributions,” Mooring said. “Clinicians in the Circumpolar North should become familiar with borealpox and the potential that it may lead to severe disease in immunocompromised patients.”
