Highly fatal tick-borne infections surge in Japan, prompting outdoor activity warning

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 bloodsucking 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 characterised by a high fatality rate of 27 per cent. After an incubation period of 6-14 days, symptoms such as fever, vomiting and diarrhoea 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