very year, an estimated 60 million people around the world contract dengue fever. The dengue virus is classified into four serotypes, i.e. genotypes as defined by specific sets of antigens. Infection with one results in lifelong immunity to that serotype but may predispose a person to the more severe dengue haemorrhagic fever (DHF) when he or she is infected with one of the remaining three serotypes. Without immediate treatment, a patient may die.

Aedes aegypti, the vector responsible for transmitting the virus, has adapted very well to the urban human habitat, thriving in crowded and confined spaces. Its success is causing dengue to rear its ugly head again in Singapore - and with a vengeance. Generally a few thousand adults come down with dengue fever each year, making it the most significant infectious disease in the country. The warmer weather, a result of El Nino and the resultant rise in temperature, seems to correspond to a hike in the number of people diagnosed with the fever - 456 in May alone. As of the middle of this year, more than 1,840 cases have been reported, some four times higher than for the same period in 2002. Most cases have been mild, and so far only two deaths have occurred, both in January.