Health officials in the US and Europe may soon be visiting South-East Asia for updates on the most effective means of fighting dengue fever, traditionally a poor countries' disease. A dengue outbreak was reported at the beginning of this year in Madeira, Portugal, and in 2010 there were cases of dengue recorded in Nice, France. In 2010, there were also a score of reported cases of locally contracted dengue in Miami, Florida, the first in five decades.
"Climate change may be responsible but anywhere that it is getting warmer, the aedes aegypti mosquito will be able to transmit the dengue virus longer," said Pratap Singhasivanon, dengue expert and professor in tropical medicine at Thailand's Mahidol University.
The warm South-East Asian region has typically accounted for a large share of dengue cases worldwide, with the virus normally peaking during the rainy season. It has been a priority health challenge for decades. This year is no exception. In Thailand, from the start of the year until June 4, a total of 39,029 people have been treated for dengue, a threefold jump compared to the same period in 2012. At least 44 have died.
Dengue epidemics tend to shift from country to country and year to year in South-East Asia, as populations build up immunity to one strain of the virus, then get hit by a different one. Last year, Vietnam reported 87,000 cases of dengue, up 25 per cent compared with 2011. There were 79 deaths. During the first five months of 2013, there were 13,903 dengue cases in Vietnam, down 7 per cent year-on-year, with only two deaths.
Famously hygienic Singapore has been hard hit this year by its worst dengue epidemic since 2005. The city-state has recorded more than 9,000 cases of dengue since January, with two deaths. Mid-year figures are already twice the number of cases in 2012. The Jakarta Health Agency said there had been 3,119 known cases of dengue in the Indonesian capital through May, with seven fatalities.
Malaysia recorded 10,401 dengue cases nation-wide through May, up 1 per cent from last year, with 19 deaths, compared with 20 in the same period in 2012. The number of dengue cases in the Philippines rose 1.9 per cent to 37,895 through May 25. "The cases are increasing because the population is increasing," said Philippines' Health Under-secretary Teodoro Herbosa. "The urban centres are increasing, so dengue is one of our public health problems."
Dengue is transmitted by the aedes aegypti mosquito, an urbanite that likes to breed in receptacles of standing water that abound in South-east Asian cities, especially in the rainy season. The best way to beat dengue is to deprive the mosquito of its favoured breeding spots. The Philippines has launched a "4 o'clock habit" campaign, urging residents to clean their homes each day.
"Nothing beats prevention," Herbosa said. Malaysia is experimenting with the release of mutant mosquitoes with fatal genes designed to kill the offspring. "The trial run will determine how we can control dengue in the real world," said Rose Nani, chief of Malaysia's Vector-Borne Disease Station. Researchers at Singapore's Nanyang Technological University have developed a mobile phone application which allows residents to photograph mosquito breeding grounds to send to health authorities.
Thailand has been at the frontline of experimenting with a dengue vaccine, using school children in Rathchaburi province for trial runs of the French pharmaceutical firm Sanofi SA's drug. Initial field tests of the vaccine last year found that it was only effective in immunizing against three of the four dengue serotypes. Further field tests are under way by Sanofi in 10 countries, with results expected in April. Research on a dengue vaccine has been underway for the past three decades, without a breakthrough, partly because of the difficulty of providing immunity against all four strains of the virus in one drug.
"But I think we will have a dengue vaccine before a malaria vaccine," Pratap said. "Even if the Sanofi vaccine doesn't work there are four or five others in the pipeline." That might be reassuring for rich countries, but a vaccine might not prove a panacea for South-East Asia. "Even if the vaccine proves effective, it doesn't mean a dengue vaccination will be a national programme because we have to take into account the cost," said Andi Muhadir, director of Indonesia's Vector-Borne Disease Control Department.