Ticks can carry a variety of infectious pathogens. Once the ticks bite humans, humans can then be infected with illnesses ranging from babesiosis and Powassan disease to Lyme disease. Now, according to Medical XPress, a novel (previously unknown) tick-borne illness has been discovered in Japan: the Yezo virus.

After two separate incidences in which patients pursued medical attention for tick bites, doctors screened the patients for tick-borne illnesses. Yet no known viruses from the region showed up on the tests. Eventually, after further testing, doctors discovered the Yezo virus, a type of orthonairovirus part of the greater class of nairovirus. So what do we know about this novel virus, and what are we looking to learn moving forward?

For more insight into the research findings, take a look at this article published in Nature Communications.

Yezo Virus

In 2019, a 41-year-old male made his way to the hospital in Hokkaido, Japan. He believed that he had been bitten by a tick and was experiencing a number of side effects, such as leg pain and a fever. To determine what his condition was, doctors performed a number of tests. However, all of the tests showed that whatever the man had was not a regionally known virus. The man did not die and was sent home two weeks later.

One year later, in 2020, another patient came to the hospital. This patient, too, had been bitten by a tick and was experiencing similar symptoms. Similarly, the tests came back with no regionally known virus.

Soon, researchers and scientists from Hokkaido University began running genetic virus analysis, evaluating blood samples sourced from the two above patients. These analyses highlighted how the patients were actually infected with a novel orthonairovirus, which they decided to call Yezo virus.

The Research

But was this virus confined to these two patients, or had it spread? To determine this, researchers sourced blood samples from hospitalized patients with tick bites over a 7-year period. These showed that at least 5 other patients had had Yezo virus, with symptoms including:

• High fever
• Leg pain
• Abnormal liver function
• Reduced platelets (thrombocytopenia)
• Lowered leukocyte (a type of white blood cell) levels

Further research highlighted a few other insights about the Yezo virus:

• The virus seems to have began in raccoons and shika deer, both of whom had Yezo virus antibodies.
• At least three tick species were proven to carry the virus.
• Yezo virus is similar to other viruses found in Uzbekistan (Tamdy) and Romania (Sulina).
• None of the seven cases resulted in death. However, researchers are unsure how many other people outside of Hokkaido have had Yezo virus; whether it has caused any deaths in other areas; or where, if at all, the virus has spread.