The health ministry confirmed Tuesday that the tick-borne disease thrombocytopenia syndrome, or SFTS, was responsible for the death of an adult male in Hiroshima last summer, bringing the number of known domestic fatalities to four. Nine other similar deaths are being investigated.
Here are some questions and answers regarding SFTS.
What is SFTS?
SFTS, an acronym for severe fever with thrombocytopenia syndrome, has been observed since around 2009 in China. Following an incubation period that can last between six to 14 days, a patient infected with the virus can experience high fever, nausea, diarrhea and reduced blood platelet count as well as reduced white blood cells.
There are no effective vaccines or remedies and the rate of death from SFTS is between 10 to 30 percent, according to the National Institute of Infectious Diseases.
How did the disease come to light in Japan?
It began with the death of a woman in Yamaguchi Prefecture last fall. Symptoms shown by the patient were similar to those reported in SFTS patients overseas, and blood tests finally confirmed in January that infection caused the death.
Confirmation was also made this month that a person who died earlier in Ehime Prefecture succumbed to SFTS, as did another in Miyazaki Prefecture. Then came Tuesday's finding regarding the Hiroshima.
How is the SFTS virus transmitted?
Ticks are considered the prime suspect at this point, since many of the cases in China were found to originate from tick bites.
But no traces of tick bites have been found in any of the four Japanese who died from SFTS. Thus, the NIID states that it is "unclear" how the four Japanese victims were infected, although they say they likely came into contact with the disease inside Japan and not during visits overseas.
The NIID says the SFTS virus probably was already present in Japan, and it will study the circumstances to shed light on the recent developments.
What is the difference between regular ticks and those that cause the disease?
Those carrying SFTS differ from house dust mites and mites carried by mice. The culprits carrying the virus are ticks that live outside in the grass and are about 3 to 4 mm long. They become active in warm weather.
Ticks carrying the virus can be found throughout Japan, but the health ministry says it must wait until later in the year to do a thorough study.
"We can't conduct our studies until they come out (and are active). But when the season comes, we will quickly carry out our research" on the ticks and SFTS, health minister Norihisa Tamura told reporters last week.
Are there any other diseases that are caused by tick bites?
About 180 cases of Japanese spotted fever and 10 cases of Lyme disease are observed annually in Japan.
According to the NIID, tick bites can be deep and the arachnids can continue to suck blood for hours or even days. Unlike the bite of house dust mites, which can cause itching, a tick bite can go unnoticed and may cause no pain or itchiness.
Pieces of a tick can break off and remain in the skin if it is removed by force, so the institute recommends seeing a doctor for proper treatment.
How can one avoid catching the disease?
Avoiding being bitten is crucial to preventing infection. The health ministry and the NIID recommend wearing long sleeves and long pants when walking in thickets and high grass.
"One should be extra careful between spring and autumn, when ticks are active," the institute states.