The first cases of dengue fever to be reported in Japan in 70 years sent government health officials scrambling to fumigate Yoyogi Park, where so far at least 22 people -- none of whom have traveled abroad recently -- are believed to have contracted the disease from mosquito bites.
The dengue outbreak, reports Yukan Fuji (Aug 31), was not entirely surprising, as it has been predicted for some time now that climate change is likely to make Japan increasingly vulnerable to tropical diseases, including dengue fever, West Nile fever, malaria and yellow fever.
The first person reported to have been infected with the dengue virus was a teenage girl from Saitama Prefecture. She was followed by a Tokyo male in his 20s and another female. Ground zero for the infection in all four cases was Yoyogi Park.
"In the future we may be getting reports of new cases from all over the place," predicted University of Tokyo Prof Atsuro Hamada.
About half the cases of dengue fever are asymptotic, and only a very small percentage of people who contract it, around 1%, become violently ill. As such, the disease itself isn't a major problem. Rather, the problem is what made it possible for an outbreak of dengue to occur in Tokyo.
"There are concerns that it might be related to the rise in average temperatures due to climate change," a source at the Environment Ministry is quoted as saying. "This year, there have been frequent heavy downpours, and the volume of rainfall has been heavier than in previous years. We believe this is producing more mosquitoes and other carriers of viruses, creating more factors that enable the spread of diseases."
The World Health Organization (WHO) has also noted that irregular weather patterns brought on by the El Nino phenomenon cause heavier precipitation. Epidemics of cholera were frequent occurrences in South America up to 1990 in years when ocean temperature rose as a result of El Nino.
The Asian tiger mosquito that transmits Dengue fever had previously not been found north of the Kanto area, but recently it has moved as far north as Morioka in Iwate Prefecture. This indicates the high likelihood that changing weather patterns are enabling carriers of tropical diseases to spread to increasingly wider parts of the archipelago.
And dengue may just be the beginning. In 1999, New York City first reported cases of West Nile fever (WNF), common in Uganda and other African countries. It has since spread from Canada to the Caribbean, and killed 286 people in the U.S. in 2012, with Texas being the hardest hit. No vaccine to prevent it exists.
"WNF is now spread in North America, Africa, and Europe to Central Asia," says Dr Yoshikazu Shirai, an authority on vermin. "The Culex and Asian tiger mosquito, which inhabit Japan, are both carriers of the virus, which can be spread by migratory birds. And once the virus arrives at a locale, there's the danger that infections will spread."
Dr Shirai says that malaria, of which cases have not appeared for over 50 years, used to be common in Japan, which is why caution is warranted.
"Epidemics happened many times in the past," Shirai said. "Now there's a danger of 'airport malaria,' in which virus-bearing mosquitoes fly into the country aboard passenger jets.
"The distribution of the Asian tiger mosquito is spreading," he adds. "In addition to the dengue virus, it can also carry yellow fever, the disease that took the life of humanitarian physician Hideyo Noguchi in Ghana. It's a fearsome virus that kills from 30% to 50% of those infected."
The outbreak of dengue fever in Yoyogi Park might very well be a harbinger of even nastier things to come.© Japan Today