The first reported case involving the new virus was recorded in Japan in 2019. At that time, a 41-year-old man was admitted to hospital with fever and leg pain after suffering a tick bite during a stroll through a forest on the Japanese island of Hokkaido.

The man, who was successfully discharged from the hospital following two weeks of treatment, tested negative for all tick-borne viruses known at that time. Researchers from Hokkaido University, including Dr. Keita Matsuno, a virologist at the university’s International Institute for Zoonosis Control, subsequently analyzed the patient’s blood samples and discovered a new virus.

The team presented its research results in the journal ‘Nature Communications’ in late September. The new virus turned out to be a part of a family of 15 species called ‘nairoviruses’, four of which can cause disease in humans.

One of the nairoviruses is known to cause Crimean–Congo hemorrhagic fever, which manifests as muscle pains, diarrhea and bleeding into skin, potentially leading to liver failure and death. The novel virus appears to be most closely related to the Sulina virus and Tamdy virus, found in Romania and Uzbekistan, respectively. The Tamdy virus reportedly caused acute fever in China in recent years, according to research published in 2020.

The new Yezo virus could cause high temperatures up to 39 degrees Celsius, as well as reduce the number of blood platelets and while blood cells – or leucocytes – responsible for protecting the human body from infectious agents like bacteria and viruses.

The researchers then analyzed the blood samples of some other patients with similar symptoms starting from 2014. “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.

The scientists also sought to discover the source of the virus, finding that Yezo virus RNA was present in three major tick species across the northern Japanese island. Antibodies to the virus were also found in deer and raccoons inhabiting the area. Now the researchers believe that testing for the new disease outside of Hokkaido is of utmost importance. The team plans to track potential nationwide distribution of the virus in humans and animals alike.

“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,” they said.