An epidemic could take an economic toll, says the World Health Organisation. Chikungunya symptoms were first recorded in India as early as 1824. The virus was first identified in Tanzania in 1952. Outbreaks have occurred in Indonesia, Myanmar and Vietnam as well as in India, which has recorded more than 1.25 million cases. But it was on the French Indian Ocean island of Reunion in 2005 and 2006 that chikungunya demonstrated its devastating impact. Striking nearly 40 per cent of 785,000 people, it caused US$160 million in tourism losses alone. That was disabling to Reunion. Then came an alarming finding: Genetic mutation has made the Asian tiger mosquito - Aedes albopictus - as efficient a carrier of the virus as the Aedes aegypti. In 1965, a Singapore tiger specimen had also yielded a dengue type-2 virus. So, the most prudent measure is to target both the usual Aedes suspects.

Vector control, begun in Singapore in 1966, succeeded by 1973 in reducing from nearly 50 per cent to 2 per cent premises found to harbour the Aedes larvae. Thereafter, a 15-year dengue lull might have lowered 'herd' or general immunity, ironically setting the stage for a resurgence. Dengue now strikes adults of both genders more often than it does children and women, as mosquito breeding is found more frequently in workplaces than in the home. The case and cluster detection and containment strategy used by the health authorities are an efficient use of public health resources, but may need refinement. A shift back to island-wide mosquito surveillance and control, even if more expensive, may be warranted if the same vector spreads chikungunya beyond Little India and raises the dengue incidence. In either approach, however, stricter enforcement and heavier fines for repeat offenders as well as public education still matter.