A type of tick that transmits SFTS (©the National Institute of Infectious Diseases [NIID])
Nasty outdoor ticks are becoming a scourge in Japan in 2025. The cumulative number of patients in Japan who have contracted the tick-borne hemorrhagic viral infection "Severe Fever with Thrombocytopenia Syndrome" (SFTS) has reached a record high.
A preliminary report in early August showed that the number of SFTS patients had risen to 135. That surpasses the previous record for the highest number of patients in a single year set in 2023. More than 10 deaths have been confirmed so far in 2025. Moreover, in the mid-August obon holiday week, 143 cases were reported in five prefectures.
Approximately 90% of SFTS patients in Japan are over 60 years old, and the mortality rate is estimated to be 10-30%.
A real sense of urgency is needed to gain control over the spread of this infection. The government must step up its vigilance and response.
How Do You Get SFTS?
SFTS is usually transmitted outdoors through tick bites. Once a person is infected, after an incubation period of around 10 days, symptoms such as fever, vomiting, and diarrhea appear. Gum bleeding and bloody stools may also occur due to a decrease in platelets.
The SFTS virus was first discovered in China in 2007, and the causative virus was isolated in 2010. In Japan, the first confirmed case appeared in 2012.
Climate change has been pointed to as a factor behind the recent increase in the number of patients. As tick-friendly habitats expand, the distribution of SFTS patients is spreading from western to eastern Japan. Hokkaido reported its first case earlier in 2025.
People should be aware that there is now a risk of infection anywhere in Japan.
Reducing Risk for Humans and Pets
Everyone needs to be careful when engaging in outdoor leisure activities or farm work from April to October. Those are the months when ticks are most active. When camping, hiking, or entering the mountains, wear long sleeves and long pants to avoid exposing your skin. Also, avoid walking in grassy areas while wearing sandals or similar footwear.
There are insect repellents on the market that contain substances like DEET or Icaridin (Picaridine), which are effective against ticks. They must be used as intended, as the target age group and duration of use vary depending on the concentration.
Infections are not limited to humans either. An increasing number of dogs, cats, and other pets are also becoming infected by SFTS. The cumulative number of such cases recorded over the past 10 years is around 1,100. However, the mortality rate for these animals is in the 60% range, which is higher than that for humans.
Animal-to-Human Transmission
There are also reports of the virus being transmitted from animals to humans. Since the disease can be transmitted through bodily fluids, people should avoid contact with the saliva, tears and excrement of sick pets.
Using insect repellent meant for pets on dogs and cats that spend time outdoors can prove helpful in mitigating the risk. So can brushing them down when they come home from outside.
Officials have confirmed that a veterinarian in Mie Prefecture died from SFTS in June 2025. All health professionals must exercise due caution, including wearing protective gear, when conducting examinations of humans or animals.
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(Read the editorial in Japanese.)
Author: Editorial Board, The Sankei Shimbun
