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Entomologists are warning lovers of Japan’s great outdoors to beware of ticks that have until recently been more commonly found in warmer regions, such as India, Thailand, and Indonesia.

Several species of these ixodid ticks – which can transmit the virus that can cause potentially fatal thrombocytopenia syndrome (SFTS) – have now been discovered in the Tohoku region of northern Japan, indicating that they are expanding their range from an initial foothold in western Japan.

Researchers believe the insects are extending their range as temperatures around the world increase, with no fewer than nine species of tick located on an island off Tohoku during surveys between June and August 2021, the researchers said in a paper published in the academic journal Experimental and Applied Acarology in July.

Ticks are generally understood to spread when they attach themselves to deer, boars, and other wild mammals. However, it appears they are also expanding their habitats by hitching rides on migrating birds.  

Ticks can get onto the clothing or skin of humans walking in rural areas and experts warn that a bite may not be immediately noticed. The experts also caution that ticks can use a family pet as a host and be transferred into the home.  

The primary symptoms include a fever, vomiting, diarrhea, and rectal bleeding. A visit to a hospital may also reveal a low platelet count, depressed white blood cell counts, and elevated liver enzyme levels. In extreme cases, SFTS can lead to multiple organ failure and death.  

According to the National Institute of Infectious Diseases, there were 95 cases of people being infected with the virus between the turn of the year and the end of July. The authorities reported five fatalities from the virus in the same period.  

SFTS was first identified in Japan in 2013, with 40 cases reported to authorities, but that had risen to 118 cases in 2022.  

In one of the most recent cases, a woman in her 80s from Fukuoka died in August after contracting SFTS through a tick bite. Local health authorities advised people walking in overgrown areas to wear shirts that cover their arms and long trousers.  

The increase in incidents in Japan mirrors similar developments elsewhere in the world. The first case of tick-borne encephalitis virus in Great Britain was of a 50-year-old cyclist who was bitten in North Yorkshire. Local authorities say the illness was unheard of in the UK until recently and that rising global temperatures are enabling the insects to survive in environments that would have been prohibitively cold even two decades ago.