The first case of dengue fever was reported on Aug. 27. As of Friday, the number had increased to 141 people in 17 prefectures — not one of whom had traveled abroad. If the asymptotic or unreported cases are included, it’s quite possible that figure may be two or threefold.
This deservedly made news for being the first outbreak in Japan since 1942-44 — a time when thousands of Japanese soldiers had been dispatched to the tropics.
According to the National Institute of Infectious Diseases, reported cases of dengue fever in Japan numbered 402 in 2013, but all were believed to have been contracted abroad.
Ground zero for most of the infections was traced to Yoyogi Park, an expansive patch of greenery in Tokyo’s Shibuya Ward. The culprits were a 4½-mm-long breed of mosquito called hitosujishimaka in Japanese, and referred to as the Asian tiger mosquito — scientific name Aedes (Stegomyia) albopictus — in English.
“The lifespan of a mosquito is about one month, and over that period, it might feed on blood two or three times,” Koichiro Fujita, professor at the University of Human Arts and Sciences in Saitama, tells Shukan Post (Sept. 19-26). “If you consider the number of people infected, you’re looking perhaps at 100 mosquitoes carrying the virus.”
Fujita suspects the source of the contagion might have been the ASEAN Festival held at Yoyogi Park on Aug. 1 and 2.
“The event was visited by many people from Southeast Asia,” he says. “It can be assumed that the mosquitoes bit people infected with the dengue virus and then subsequently bit Japanese.”
Because the mosquitoes’ habitation of choice is wooded areas, it’s unlikely they will invade the entertainment zones in nearby Shibuya or Shinjuku, Fujita adds.
“For dengue to spread widely it would need ideal conditions of an appropriate number of mosquitoes and human hosts,” he pointed out. “So the present outbreak in Japan can be regarded as an extremely rare case.”
One reason the outbreak captured the public’s attention was that one of its first known victims was Saaya (she goes only by her first name), a well-known guradoru (“gravure doll,” i.e., pin-up girl).
The 20-year-old Fukuoka native burst onto the scene six years ago when an early onset of maturity increased her measurements — making her a favorite of the rorikon (Lolita complex) crowd.
Friday (Sept. 19) reports that Saaya was probably infected during a shooting engagement in Yoyogi Park on Aug. 21.
“Her fever soared over 40 degrees and she felt intense pain in her eye sockets,” her manager told the magazine. “She couldn’t eat a bite for two or three days. Her appetite has gradually returned, but she told me she was covered with itchy red blotches on her arms and legs.”
“We don’t know if it was a foreigner or a Japanese who brought the virus back from abroad, but as a result of warming on a global scale the Asian tiger mosquito that serves as a carrier for the dengue virus has spread as far north as Aomori,” Shuzo Kanagawa, medical director of the Travel Clinic at the National Center for Global Health and Medicine, tells Friday magazine. “It’s one of the most common breeds of mosquitoes in Japan.”
Shukan Asahi (Sept. 26) suspects the disease has been lurking here at least since 2013.
“Last year, a woman who flew from Japan to Germany was diagnosed with dengue after her arrival there,” Koichi Morita, a professor of tropical medicine at Nagasaki University, tells Shukan Asahi. “She was believed to have contracted it while in Japan.”
In any event, dengue fever is certainly not something to be taken lightly.
“In terms of lethality, it’s not so dangerous compared with West Nile virus or Ebola,” says the aforementioned professor Morita. “But if you look at it from a worldwide perspective in terms of sheer numbers, far more people are infected by dengue and far more die from it.”
Despite closing sections of Yoyogi Park for fumigation, Shukan Gendai (Sept. 20-27) frets that it may be next to impossible to completely eradicate those pesky mosquitoes. “The eggs of the Asian tiger mosquito can hatch in just small amounts of water inside an empty can or discarded tire,” says Ichiro Miyagi, professor emeritus at Ryukyu University. “Even without water the eggs can survive for one or two months. The mosquitoes lay 100 to 200 eggs at once, four to five times during their brief lifetime. It’s one of the hardiest breeds living around humans.”
With the imminent onset of cooler weather, the question now being asked is, Will the mosquito problem fade away of its own accord, or will it become a long-term headache for public health authorities in the runup to the 2020 Olympics, the main stadium for which borders on — you guessed it — Yoyogi Park?
Writing in Asahi Geino (Sept. 25), columnist Kazuyuki Izutsu lambasted Tokyo Gov. Yoichi Masuzoe, whom he accuses of taking a lackadaisical attitude toward dengue’s potential threat.
“Six years from now, there’s no guarantee it will be eradicated,” Izutsu says. “It might get to the point that dengue becomes so widespread, it won’t be safe for people to go outside in the summer. If that happens, no part of Japan will be suitable to host the Olympics.”