New Tick-Borne Virus Discovered in Japan

by johnsmith

Scientists have isolated a new orthonairovirus from two patients showing acute febrile illness with thrombocytopenia and leukopenia after tick bite in Hokkaido, Japan.

Transmission electron microscopy of YEZV particles negatively stained with 2% phosphotungstic acid. Image credit: Kodama et al., doi: 10.1038/s41467-021-25857-0.

Transmission electron microscopy of YEZV particles negatively stained with 2% phosphotungstic acid. Image credit: Kodama et al., doi: 10.1038/s41467-021-25857-0.

Orthonairoviruses are tick-borne viruses in the genus Orthonairovirus, the family Nairoviridae.

They cause sometimes fatal febrile illnesses in humans and other animals.

Of 15 species within the genus, four species comprise known human pathogens: Crimean-Congo hemorrhagic fever virus, Nairobi sheep disease virus, Dugbe virus, and Kasokero virus.

The newly-discovered orthonairovirus, named Yezo virus (YEZV), is the causative agent of an acute febrile illness characterized by thrombocytopenia, leukopenia, and elevation of liver enzymes and ferritin.

“At least seven people have been infected with this new virus in Japan since 2014,” said Dr. Keita Matsuno, a virologist in the International Institute for Zoonosis Control at Hokkaido University.

The Yezo virus was discovered after a 41-year-old man was admitted to the hospital in 2019 with fever and leg pain after being bitten by an arthropod believed to be a tick.

“In mid-May 2019, he visited a forest area near Sapporo for approximately 4 hours,” the researchers said.

“The next day, he noticed and removed an arthropod attached to his right abdomen. Four days after visiting the forest, he had a fever over 39 degrees Celsius, followed by gait disturbance and leg pain.”

“After the fever continued for 4 days, he was admitted to our hospital with a temperature of 38.9 degrees Celsius. On admission, a review of systems was negative except for a fever, appetite loss, and bilateral lower extremity pain.”

The patient was treated and discharged after two weeks, but tests showed he had not been infected with any known tick-borne viruses.

A second patient showed up with similar symptoms after a tick bite the following year.

“The patient was a 59-year-old previously healthy male with no remarkable medical history living in Sapporo, Hokkaido,” the scientists said.

“In mid-July 2020, he hiked on a mountain near Sapporo. During the hike, he received a bite on his lower leg from an unidentified arthropod that remained attached for at least 30 min..”

“He remained in his usual state of health until 9 days after the hike when he lost his appetite and then, developed a fever of 37.4 degrees Celsius on 17 days after the hike.”

“Following two visits to different hospitals on days 3 and 4 after the onset of fever, where he was found to have a fever (38.5  degrees Celsius on day 3) with leukopenia and thrombocytopenia, he visited our hospital on day 5 post-onset of fever.”

The genetic analysis of viruses isolated from blood samples of the two patients revealed a new type of orthonairovirus, which is most closely related to Sulina virus and Tamdy virus, detected in Romania and Uzbekistan, respectively.

To determine the likely source of the virus, the team screened samples collected from wild animals in the area between 2010 and 2020.

They found antibodies for the virus in Hokkaido sika deer and raccoons. They also found the virus RNA in three major species of ticks in Hokkaido.

“The Yezo virus seems to have established its distribution in Hokkaido, and it is highly likely that the virus causes the illness when it is transmitted to humans from animals via ticks,” Dr. Matsuno said.

The team’s paper was published in the journal Nature Communications.


F. Kodama et al. 2021. A novel nairovirus associated with acute febrile illness in Hokkaido, Japan. Nat Commun 12, 5539; doi: 10.1038/s41467-021-25857-0

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