Yezo virus (''Orthonairovirus yezoense'') is a species of virus in the genus ''

Orthonairovirus ''Orthonairovirus'' is a genus of viruses in the family '' Nairoviridae'' of the order '' Hareavirales'' which includes viruses with circular, negative-sense single stranded RNA. The name is derived from the Nairobi sheep disease which affect ...

'', discovered 2021 in Japan, circulating in mammals and ticks, causing a mild febrile illness in humans.

Virology

Yezo virus is classified into the genus ''

'' and is phylogenetically grouped with Sulina virus.

Natural reservoir

As of 2021, Yezo virus was found in wild deer, raccoons, and ticks from

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

, the northernmost island in Japan. They were not found in Hokkaido raccoon dogs (''Nyctereutes procyonoides albus'') or rodents (''Myodes rufocanus bedfordiae'' and ''Apodemus speciosus''). Among the three major tick species in Hokkaido ('' Haemaphysalis megaspinosa'', '' Ixodes ovatus'', and ''

Ixodes persulcatus ''Ixodes persulcatus'', the taiga tick, is a species of hard-bodied tick distributed from Europe through central and northern Asia to China and Japan. The sexual dimorphism of the species is marked, the male being much smaller than the female. H ...

'') Yezo virus was most commonly detected in H. megaspinosa. It is suspected to circulate in

Ixodes ''Ixodes'' is a genus of hard-bodied ticks (family Ixodidae). It includes important disease vectors of animals and humans ( tick-borne disease), and some species (notably '' Ixodes holocyclus'') inject toxins that can cause paralysis. Som ...

ticks as well, so the geographical range may extend much further into Asia and Europe. In 2024, Yezo virus was also found in 0.5% of ''

'' ticks in Inner Mongolia,

Heilongjiang Heilongjiang is a province in northeast China. It is the northernmost and easternmost province of the country and contains China's northernmost point (in Mohe City along the Amur) and easternmost point (at the confluence of the Amur and Us ...

, and

Jilin ) , image_skyline = Changbaishan Tianchi from western rim.jpg , image_alt = , image_caption = View of Heaven Lake , image_map = Jilin in China (+all claims hatched).svg , mapsize = 275px , map_al ...

in Northeastern China.

Symptoms and signs

In 2019 and 2020 two patients in Hokkaido, Japan had an acute febrile illness with

thrombocytopenia In hematology, thrombocytopenia is a condition characterized by abnormally low levels of platelets (also known as thrombocytes) in the blood. Low levels of platelets in turn may lead to prolonged or excessive bleeding. It is the most common coag ...

and

leukopenia Leukopenia () is a decrease in the number of white blood cells (leukocytes). It places individuals at increased risk of infection as white blood cells are the body's primary defense against infections. Signs and symptoms Symptoms may include: * s ...

lymphocytopenia Lymphocytopenia is the condition of having an abnormally low level of lymphocytes in the blood. Lymphocytes are a white blood cell with important functions in the immune system. It is also called lymphopenia. The opposite is lymphocytosis, which r ...

, coagulation disorder, and increased levels of liver enzymes after a tick bite. As of 2021, it was the first orthonairovirus associated disease in Japan. In retrospective screening. 7 people out of 248 suspected as having a tick-borne disease were found to have evidence of Yezo virus infection. In 2024, a younger person from China without underlying disease was described with a mild form of infection: light headache, dizziness, blurred vision, shortness of breath, fatigue, and

arthralgia Arthralgia () literally means ' joint pain'. Specifically, arthralgia is a symptom of injury, infection, illness (in particular arthritis), or an allergic reaction to medication Medication (also called medicament, medicine, pharmaceuti ...

. All persons in the 2 countries recovered completely.

References

{{Taxonbar, from=Q108908103 Nairoviridae