“At least seven people have been infected with this new virus in Japan since 2014, but, so far, no deaths have been confirmed,” said researcher Keita Matsuno.
Identifying an unknown virus
Researchers were previously unable to properly identify the Yezo virus because of the low number of cases. Between 2019 and 2020, two patients were admitted into a hospital in Hokkaido after receiving tick bites and testing negative for all of the common tick-borne illnesses.
After testing the patients’ blood for genetic components of different viruses, the researchers determined that the infection was linked to a new nairovirus. The name Yezo virus came from its place of origin; Yezo is a historical reference to the region of Hokkaido.
The researchers then set out to see if local animals were similarly affected by the virus, and what other cases, if any, existed in humans prior to 2019. Based on antibody tests on several different animals, there were traces of the virus in local raccoons and deer.
“The Yezo virus seems to have established its distribution in Hokkaido, and it is highly likely that that virus causes illness when it is transmitted to humans from animals via ticks,” said Matsuno.
As for other cases of the virus in humans, the team tested blood samples of patients who were admitted into the hospital with similar symptoms between 2014 and 2019 but had received an inconclusive diagnosis. They ultimately identified five other patients who had tested positive for Yezo virus, and the symptoms were consistent across the board.
Now, the researchers plan to investigate Yezo virus even further to determine other places around the world where patients could be affected by it. The COVID-19 pandemic has illustrated how quickly animal-borne infections can spread, making future studies on this virus even more important.
“All of the cases of Yezo virus infections we know so far did not turn into fatalities, but it’s very likely that the disease is found beyond Hokkaido, so we need to urgently investigate its spread,” Matsuno said.