Japanese researchers have shown that the newly discovered virus, which spreads ticks, has been causing human disease since at least 2014. The Yezo virus, as its discoverers christened it, is supposed to cause a reduction in the number of white blood cells, a drop in platelets, and also a fever, like other tick-borne diseases.
In the article published in the journal Nature Communications The researchers put forward their arguments for that Yezo virus is a new human virus. He was to appear for the first time in a 41-year-old man who was admitted to a hospital in Sapporo, Japan, in mid-May 2019, with a high fever, loss of appetite, and pain in both lower limbs.
A new virus transmitted by ticks
Symptoms occurred in “Patient 0” four days after visiting a nearby forest and three days after finding a tick attached to the right side of the abdomen. Tests showed that he had low levels of white blood cells and platelets, a component of blood that helps clot blood to prevent bleeding.
Doctors originally assumed that he had a tick-borne disease and therefore gave him various antibiotics. During 19 days, 15 of which he spent in the hospital, the patient gradually recovered and his symptoms subsided. All the while, however tests did not show infection by any known tick-borne diseasesuch as Lyme disease, tularemia or tick-borne encephalitis.
More than a year later – specifically in July 2020 – doctors came across another patient with similar symptoms. During treatment, he was hospitalized and examined in three hospitals. In the end, however, he also recovered successfully.
Traces of an unknown virus
The scientists eventually succeeded identify traces of the same unknown virus in the blood of both patients. In addition, they were able to obtain enough sample from the blood of the second patient to be able to grow it in the laboratory on mice in a completely intact state.
In the end, they managed to genetically identify the mysterious bacillus from these samples as a member of a family of viruses that spread ticks – orthonairovirus. They decided to tentatively call it Yezo virus, which refers to the historical name of the larger island of Hokkaido, where it was first identified.
Prove that a newly discovered virus it can be transmitted to humans and cause disease, however, requires some evidence that the authors, according to them, have gathered. For example, they say they have found antibodies to the Yezo virus in wildlife on the island of Hokkaido and in three major species of ticks that are known to inhabit the area.
Yezo is the cause of a febrile illness
Most importantly, the researchers found evidence of Yezo virus infection in preserved blood samples from at least five other people suspected of having tick-borne disease as early as 2014. These patients, like the first two, developed fever and reduced platelet count.
Blood tests of a total of four patients confirmed the level of antibodies against the Yezo virus after they healed. This is exactly what would be expected from an acute infection. Interestingly, four of these patients also showed signs of Lyme disease, suggesting that they may have been infected with two viruses at once.
“In this work, we have shown that Yezo is highly likely to cause febrile illness, the first report of an endemic infection associated with a potentially tick-borne orthonairovirus in Japan.” the authors wrote at the end of their study.
Further research is needed
Until the Yezo virus is finally confirmed, independent verification by other scientists will be required. However, the authors suspect that may be more widespreadthan is currently documented and are pushing for further research to be carried out as soon as possible.
“Not a single case of the Yezo virus that we know of so far has ended in death, but it is very likely that the disease occurs outside Hokkaido, so we need to investigate its spread as a matter of urgency.” said Keita Matsuno, a virologist at the International Institute for the Control of Zoonoses (Infections Naturally Transmissible between Animals and Humans).