Tokyo, futuristic metropolis of the 21st century, is grappling with a public health problem it hasn't seen since World War II -- dengue fever.
Nearly 150 confirmed and suspected cases of the tropical disease have been recorded in recent weeks. The cause? Infected mosquitoes lurking in public parks, possibly introduced by travellers.
Worries about the spread of dengue fever, the painful and potentially lethal illness that dengue virus can produce, have sparked new interest in smartphone apps that purport to repel mosquitoes with sound.
Dozens of applications that claim the power to banish bugs by emitting high-frequency sound through smartphone speakers can be found on Apple's App Store and Google Play.
Anti Mosquitoes Ultra Pro Free on Google Play, for instance, says it "turns your phone into an ultrasound device, sending high-pitch 12-22 KHz waves to keep mosquitoes and other nasty insects away."
The apps are getting decidedly mixed reviews, however.
"This is useless. I've been bitten three times," one user griped earlier this month about another free bug app, called Kakihi Pro.
There are also paid versions for those even more keen to put their faith in high-frequency sounds.
"They might not be as effective as strong bug spray, but if you've got a smartphone how about giving them a try?" asked an anonymous article on AppWoman, a Japanese site with articles about smartphones.
"But don't have high expectations. Think of them as a protective talisman."
Experts say they should be thought of as garbage.
"The mosquito repulsion by sound scam has been around for decades," Jonathan Day, a professor of medical entomology at the University of Florida, wrote in an email.
"High-frequency sound waves do not repel biting flies. The best deterrent is to avoid mosquitoes, control mosquitoes in and around the home, cover skin with breathable fabrics that prevent mosquito blood feeding and, when all else fails, use a repellent that provides at least one hour of protection with each application."
In the past, radio stations tried to lure listeners with the promise of anti-bug sounds playing over music, Day added. More recently, smartphone maker LG launched an air conditioner for African markets that has an ultrasonic "mosquito away" function.
Yet a 2010 review by the Cochrane Collaboration, a nonprofit group, examined 10 scientific studies and found no evidence to support the notion that sound can repel mosquitoes.
"High-pitched sounds from smartphone apps unequivocally do not repel mosquitoes," Joseph Conlon, a technical advisor to the American Mosquito Control Organization, wrote in an email. "The only recommended personal protective measures are EPA-registered repellents such as DEET, picaridin, oil of lemon-eucalyptus and IR3535."
The plethora of mosquito apps on iTunes and Google Play would seem to violate the guidelines for the sites, which prohibit false advertising.
Apple and Google did not respond to requests for information about their policy in such cases.
Meanwhile, most Tokyoites are waiting for a surefire mosquito killer to quash the threat of dengue -- the coming of winter.