Faced with the first domestic outbreak of dengue fever since 1945, the Tokyo Metropolitan Government on Tuesday set up mosquito traps in Yoyogi Park to gauge how many of the insects are carrying the disease.
The traps were placed in 10 locations in the park. They use light and carbon dioxide-releasing dry ice to attract mosquitoes into nets.
The trapped mosquitoes will be collected Wednesday, with the process being repeated once a week for the time being, officials said.
In an initial effort on the evening of Aug. 26 and the next morning, 35 mosquitoes were trapped but none were found to be carrying the virus that causes dengue fever.
Since the first dengue fever patients were confirmed last week, the total has risen to 36, all of whom recently spent time in Yoyogi Park or were nearby. All are currently listed in stable condition.
Fourteen of the cases were confirmed Tuesday. The patients range from a boy younger than 10 years old to people in their 50s.
Dengue fever, an illness found in tropical and subtropical areas in Asia, Latin America and Africa, is transmitted by tiger and dengue mosquitoes. It can’t spread directly from person to person.
Infected people are struck with a sudden fever around three to seven days after transmission, accompanied by head and muscle pains and a rash. Most patients have mild symptoms, but some may develop significant bleeding that can be life-threatening.
Officials put up warning signs around the busy park warning people to wear long sleeves and trousers, and boots or shoes instead of sandals.
The health ministry has called on anyone experiencing a high fever three to seven days after suffering a mosquito bite, whether in Yoyogi Park or elsewhere, to seek medical attention, but officials have also said that serious complications are rare.
At a news conference on Tuesday, Health, Labor and Welfare Minister Norihisa Tamura said he does not foresee infections spreading rapidly but noted that dengue fever “may become active in people in which it has been latent until now.”
The virus “is present at a certain level in the world, and Japan’s situation in this respect has not changed dramatically,” Tamura said. “Rather than explosively spreading, (infections) will come and go, and I ask that people remain calm.”
According to the ministry, 10 to 50 percent of people bitten by a mosquito carrying the virus will experience dengue fever symptoms, and of those, serious complications are limited to between 1 and 5 percent.
Tiger mosquitoes do not transmit the virus between each other during their life span, which is typically 30 to 40 days.