People warned to beware of tick-borne infections in Japan

TOKYO (Kyodo) — Japan has reported a spate of highly fatal outdoor tick-borne infections this year at a pace that could surpass the record high set in 2023.

Ticks, parasitic arachnids that inhabit outdoor spaces and tend to be active from spring to fall, are the source of an infection called severe fever with thrombocytopenia syndrome (SFTS). The National Institute of Infectious Diseases says roughly 90 people, mainly in western Japan, have been infected with the virus this year.

Infectious disease experts warn that the regions where blood-sucking parasites are biting people are expanding, and urge people to take caution to prevent the spread of the virus in “unexpectedly familiar places such as campgrounds and walking trails.”

Tick-borne infectious diseases, such as scrub typhus and Japanese spotted fever, have long been observed in Japan. The parasites can also be the source of infections such as Lyme disease.

In recent years, however, cases have been reported of infectious diseases previously undetected in humans in the country, believed to be caused by tick-borne viruses.

In 2013, Japan’s first case of SFTS was reported in Yamaguchi Prefecture, followed by the Yezo virus in Hokkaido in 2021 and a fatal case of the Oz virus in Ibaraki Prefecture in 2023.

Of the tick-borne viruses, SFTS is characterized by a high fatality rate of 27 percent. After an incubation period of 6-14 days, symptoms such as fever, vomiting and diarrhea occur. According to the national institute, there were 133 cases of SFTS reported in 2023.

Most people contracted the infections from ticks outdoors but there have been cases involving transmission from pets to humans, and even patients to their doctors.

Special attention should be paid to places near residential areas that continue to fields and mountains.

“Even if you’re not mountain climbing, you can still be bitten,” warned Hanako Kurai, head of the infectious diseases division at the Shizuoka Cancer Center and an expert on tick-borne infections.

In 2012, a team from Kawasaki Medical School that examined 426 tick bite cases found mountain climbing and highland trekking were the most common situations in which people get bitten, accounting for 237 cases, or 56 percent of the total.

However, 101 cases occurred when people were farming fields, 40 when they were picking wild edible plants, and 33 when they were tending their gardens at home. One criterion, the team concluded, was whether deer, wild boar or other wildlife were living nearby.

Tick bites often occur on a person’s neck, head or limbs, but people do not always feel pain after being bitten and may not notice immediately.

When a tick sucks blood, it expands several times larger than its body size. Experts say it is dangerous to forcibly pull out a tick that is sucking blood, because by that stage the parasite has burrowed into the host’s skin and its head or mouth-parts may twist off and remain in its host, potentially requiring medical treatment.

Progress has been made in treating tick bites. Previously, bites were only treatable if patients showed symptoms.

But the therapeutic drug Avigan, developed by Fujifilm Toyama Chemical Co., was approved by the health ministry for production and marketing for SFTS in June this year. The drug was originally stockpiled by the government as an antiviral medication used to treat new strains of influenza in Japan.

Nonetheless, Kurai of the Shizuoka Cancer Center emphasized the “importance of preventing tick bites” as the preferred method of stopping the spread of infections.

She recommended that people avoid exposing their skin by wearing long-sleeve tops, full-length trousers, hats, gloves and other clothing, as well as making sure they cover their necks with towels in woodland areas, use insect repellent and take baths following outdoor activities.