Tick-Borne Infections of SFTS Disease Increasing in Western Japan, Experts Calling for Public to Take Countermeasures

By Naomi Nagao / Yomiuri Shimbun Staff Writer

1:00 JST, September 8, 2025

The number of people contracting severe fever with thrombocytopenia syndrome (SFTS) — an infectious disease transmitted by ticks — continues rising in the country, mainly in western Japan.

Experts say one of the factors behind the increase is that wild animals have begun entering human-populated areas. They are calling on the public to take thorough countermeasures.

Ticks are found in undergrowth in the mountains and fields. An adult tick usually measures about 2-8 millimeters long. They attach to human skin and wild animals when they come in contact and continue to suck blood for as long as two weeks. No pain is felt when the insect bites.

Once bitten by a tick carrying the SFTS virus, patients often develop symptoms, such as fever, headache and diarrhea, following an incubation period of around six days to two weeks. SFTS sometimes causes kidney disorders and is estimated to have a fatality rate of 27% in Japan. There is no vaccine for SFTS, and once infected, symptomatic therapies and antivirals are used for treatment.

The first case of SFTS in Japan was confirmed in Yamaguchi Prefecture in 2013. Infections have since been reported mainly in western Japan.

As of Aug. 24, the country reported a record 142 cases this year, according to preliminary data from Japan Institute for Health Security. By prefecture, 14 patients were reported in Kochi Prefecture, followed by nine in Nagasaki, Kumamoto and Oita prefectures, and eight in Hyogo, Shimane and Kagoshima prefectures. The data showed some instances in areas where no cases had been reported previously, including Hokkaido.

“One of the factors for the increase is considered to be a rising number of wild animals that appear around residential areas,” said Masaki Yasukawa, president of Ehime Prefectural University of Health Sciences and an expert on SFTS. He suggested that deer and racoons infected with the SFTS virus are bitten by ticks in mountains and fields near areas populated by humans and the ticks that have bitten the animals are spreading the virus to humans.

Once the virus reaches human-populated areas, the risk of domesticated animals getting infected increases.

Last month, a case of a pet cat contracting the virus was reported in Toyama Prefecture.

“There is also a risk of transmission to people when infected dogs or cats bite them,” Yasukawa said. “People should not touch weak-looking animals outdoors.”

Basic prevention

To avoid SFTS infections, it is important to take measures to prevent being bitten by ticks.

When outdoors, such as going to mountains or fields, or working on a farm, it is best to wear pants and long-sleeve clothing and limit skin exposure. Spray insect repellent around the neck and the edges of shirts and pants.

Take a bath after returning home and check your body to see whether a tick has attached itself to your skin. If a tick is found on the skin, do not pull it off yourself because this may cause the tick’s mouth to remain on the skin. It is best to have the tick removed by a doctor.

Among ticks found in Japan, those carrying the SFTS virus are said to account for as much as a few percent, although the figure varies depending on the region and season, according to the Health, Labor and Welfare Ministry.

Masaru Natsuaki, the head of the dermatology department at Kinki Central Hospital in Itami, Hyogo Prefecture, said that people do not have to worry too much because the number of ticks infected with the SFTS virus is small. “If you are bitten by a tick, you should immediately go to a medical institution,” he added.