Emerging infectious disease caused by tick-borne nairovirus identified in Japan

A previously unknown virus that can infect humans and cause disease has been identified by scientists in Japan. The new infectious virus, called Yezo virus, is transmitted by tick bites and causes a disease characterized by fever and reduced blood platelets and white blood cells. The discovery was made by researchers at Hokkaido University and colleagues, and the results have been published in the journal Nature Communication.

Keita Matsuno, virologist at the International Institute for Zoonoses, University of Hokkaido, said: “At least seven people have been infected with this new virus in Japan since 2014, but so far none death has not been confirmed. “

The Yezo virus was discovered after a 41-year-old man was admitted to hospital in 2019 with a fever and pain in his legs after being bitten by an arthropod believed to be a tick while walking around a local forest in Hokkaido. He was treated and released after two weeks, but tests showed he had not been infected with any known virus carried by ticks in the area. A second patient presented with similar symptoms after a tick bite the following year.

Genetic analysis of viruses isolated from blood samples from the two patients revealed a new type of orthonairovirus, a class of nairovirus, which includes pathogens such as Crimean-Congo hemorrhagic fever virus. Scientists named it Yezo virus, after a historic Japanese name for Hokkaido, a large island in the north of the country where the virus was discovered. The new virus was found most closely related to Sulina virus and Tamdy virus, detected in Romania and Uzbekistan respectively, the latter having recently caused acute fever in humans in China.

Scientists then checked blood samples taken from hospital patients who had similar symptoms after tick bites since 2014. They found additional positive samples from five patients. These patients, including the first two, had fever and reduced blood platelets and white blood cells, and showed signs of abnormal liver function.

To determine the likely source of the virus, the research team looked at samples taken from wildlife in the area between 2010 and 2020. They found antibodies to the virus in shika deer and Hokkaido raccoons. They also found the RNA of the virus in three major tick species in Hokkaido. Matsuno said, “The Yezo virus appears to have established its distribution in Hokkaido, and it is very likely that the virus causes disease when transmitted to humans from animals via ticks.”

As the COVID-19 pandemic so dramatically demonstrates, animals carry many unknown viruses and some of them can continue to infect humans. “Not all cases of Yezo virus infection that we know of so far have turned into deaths, but it is very likely that the disease is beyond Hokkaido, so we urgently need to investigate on its spread, ”Matsuno said.

The research team now plans to track the possible nationwide distribution of the new virus in wildlife and patients. And they say more hospitals should test for the virus in patients who complain of symptoms.