Southeast Asia is bearing the brunt of the latest global push of the disease. The source is a daytime-biting mosquito, Aedes aegypti, which picks up the dengue virus from an infected human and then hands it to someone else with its next blood meal.

"Dengue fever is a growing problem in the Western Pacific Region," the World Health Organisation (WHO) says.

"Unprecedented rapid urbanization has resulted in an increasing number of people living in poor housing, with lack of proper waste disposal and inadequate drainage, creating favourable breeding conditions for the mosquito," it says.

"Despite its significance, dengue prevention and control activities are under-funded in many countries."

Last year, more than 160,000 cases of dengue were reported in the WHO's Western Pacific, a region that includes China, Japan and South Korea as well as countries of Southeast Asia.

That number seems certain to be dwarfed in 2005.

In the Philippines, the number of reported cases so far this year is 14,738, a 20-percent rise over 2004, with 197 deaths against 144 for last year.

In Malaysia, there were 102 deaths and 33,000 suspected cases of fever in 2004; so far this year, there have been 70 deaths and 27,569 suspected cases.

In Thailand, the number of cases has risen 47 percent, with 16 fatalities.

Even in Singapore, a country known for its sparkling hygiene, there have been a record 11 deaths so far this year, with almost 11,000 cases reported.

Dengue fever encompasses several forms of sickness, whose severity depends on the strain of the so-called flavivirus transmitted by the mosquito.

Symptoms typically include a high fever and headache as well as aching bones, joints and muscles that give dengue its nickname of "breakbone fever." Recovery usually takes several weeks.

Its severe, fatal form is called dengue haemorrhaegic fever, or DHF, in which the patient bleeds from the gums and nose.

Prior to the late 18th century, dengue was considered a mild, localised disease of the tropics.

Then, in 1779-80, a near-simultaneous outbreak of the fever was reported in Asia, Africa and North America, strengthening suspicions that the virus could be transported by sailing ship.

The movement of people caused by World War II caused a pandemic of dengue to arise in Southeast Asia that, according to the US Centers of Disease Control and Prevention (CDC) "has spread around the world ever since."

Today, thanks to jet travel, cross-border movements and slums, global distribution of dengue is comparable to malaria. More than 2.5 billion of the world's population of six billion live in areas at risk for epidemic transmission, the CDC says on its website. In 1970, only nine countries had DHF; today, the figure is 60.

Factors that influence the pandemic are apparently natural cycles of three years or so, as well as the implementation or end of anti-mosquito programmes, and disasters such as hurricanes, typhoons and last year's Asian tsunami.

Catastrophes such as these can displace hundreds of thousands of people to makeshift homes and shelters, making them vulnerable to getting infected and to infecting others through mosquito bites.

They may also create large areas of swampland that are ideal for mosquito breeding.

On average, around 50 million infections of dengue occur each year, of which the cases of DHF probably number around half a million, according to the WHO. At least 12,000 cases are fatal.

No vaccine for dengue exists, although Thai doctors are trialling an early prototype vaccine which, if all goes well, may be on the market within three years, the Bangkok newspaper The Nation reported on September 4.

In the absence of a medical breakthrough, the authorities have to fall back on time-honoured basics of public health.

This means taking fundamental steps such as improving water provisions and sewerage for shanty towns, encouraging the public to empty water containers and stepping up surveillance so that outbreaks of the disease are spotted at the earliest stage.

But a novel strategy has been pioneered in parts of northern and central Vietnam.

A. aegypti has been wiped out in these communities by a campaign to "seed" water tanks with a microscopic crustacean called Mesocyclops copepod, which feasts on mosquito larvae, a study published last February said. Related Links
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