Tick-borne Yezo Virus Emerges in Japan

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Yezo virus
Credit: Fumihiro Kodama, et al., Nature Communications, September 20, 2021

Scientists in Japan have discovered a novel nairovirus, called the Yezo virus that is transmitted via tick bites.

In 2019, a 41-year-old man presented to a hospital in Hokkaido, Japan with fever, loss of appetite and leg pain. He had gone for a walk in a local forest and got bit by a tick. Soon after, his symptoms began. Laboratory results had revealed low white blood cells and platelets. After two weeks, his symptoms resolved, and the man left the hospital. However, further tests revealed an unknown virus in the patient’s body; not commonly found in ticks of that region. The following year, another patient with similar symptoms after a tick bite showed up. Doctors then conducted a genetic analysis of the virus discovered in both the blood samples. This revealed the presence of a new type of orthonairovirus, a family of viruses commonly spread by ticks. They named it the Yezo virus.

Soon after, researchers began testing samples of hospitalized patients with a history of tick bites and similar symptoms. They collected data from 2014 till 2020 and were able to identify five more patients infected with the Yezo virus. To determine the source of the virus, the scientists then screened samples from wild animals in the area. They found antibodies to the virus in Hokkaido shika deer and raccoons. Furthermore, they also discovered the virus RNA in three major tick species in Hokkaido. The findings of the research are available in the journal Nature Communications.

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.

Keita Matsuno, virologist at Hokkaido University’s International Institute for Zoonosis Control

No Deaths, Yet

Tick-borne viruses have steadily increased in recent years, placing a burden on global public health. They cause an acute febrile illness in humans which can often turn fatal; especially, in rural areas.

According to the study, the Yezo virus is most closely related to the Sulina and Tamdy virus, found in Romani and Uzbekistan respectively. Their presence in wildlife in the region has caused scientists to conclude that it is likely more widespread than expected. Although no deaths have occurred so far, researchers are pushing for further research into the cases and the virus’s spread.

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.

Keita Matsuno, virologist at Hokkaido University’s International Institute for Zoonosis Control

Reference:

Fumihiro Kodama et al, A novel nairovirus associated with acute febrile illness in Hokkaido, Japan, Nature Communications (2021). DOI: 10.1038/s41467-021-25857-0

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