Yezo Virus, New Disease That Infects Humans, Discovered in Japan

Researchers in Japan have identified a previously unknown virus that can infect humans and cause disease.

Named the Yezo virus, this new virus is transmitted by tick bites and causes a disease with symptoms that include fever and a reduction in blood platelets and white blood cells, responsible for counteracting foreign substances and disease.

The Yezo virus was discovered when a 41-year-old-man was admitted to the hospital in 2019 complaining of fever and leg pain after being bitten by a tick while walking in a Hokkaido forest.

He was discharged after being treated for two weeks. The man tested negative for all tick-borne viruses that were known at the time. The following year, another patient was admitted with similar symptoms after also being bitten by a tick.

Researchers at Hokkaido University, including virologist at the university's International Institute for Zoonosis Control Keita Matsuno, performed genetic analysis on blood samples from the two patients and discovered a new nairovirus. This category of virus is named after the "Nairobi Sheep Virus" and includes Crimean-Congo hemorrhagic fever virus, both also transferred via tick bites.

The team continued to search for signs of the virus in blood samples of patients admitted to the hospital with similar symptoms since 2014. They found traces of Yezo virus in at least five more patients, all of whom demonstrated elevated fevers, reduced blood platelets and white blood cells. These patients also showed signs of abnormal liver function.

"At least seven people have been infected with this new virus in Japan since 2014, but, so far, no deaths have been confirmed," Matsuno said in a Hokkaido University press release.

The team's research is published in the journal Nature Communications.

Naming the new virus Yezo, the historical Japanese name for the island of Hokkaido where the virus was first discovered, the team set about searching for its source.

Screening blood samples taken from wildlife during a 10-year period beginning in 2010, the researchers found traces of Yezo antibodies in raccoons and Hokkaido Sika deer, which are indigenous to the region. The team also found the virus RNA of Yezo in three major tick species across the island located in the north of Japan.

Matsuno added that while there are currently no fatalities associated with Yezo, testing beyond Hokkaido and at hospitals throughout Japan is now vitally important.

He said: "All of the cases of Yezo virus infection we know of 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."

Stock image of a female deer tick. Researchers in Japan have identified a new virus, Yezo, which is transmitted to humans via tick bites. Getty