The Aedes mosquito population has grown, coinciding with the warmer-than-usual year-end wea-ther, said the National Environment Agency (NEA) yesterday .

The proportion of dengue cases due to a variant virus - the DENV-2 serotype - has also risen and they now account for half of all cases, an increase from about 44 per cent in mid-May.

This could mark an impending shift from the DENV-1 serotype that had accounted for most of the dengue cases since March 2013.

NEA said the change in the main circulating virus may be an early indicator of a future dengue outbreak. The last serotype switch, from DENV-2 to DENV-1 in March 2013, resulted in a historic high of 22,170 cases that year.

As of Oct 31, 8,520 cases have been reported. This is about 48.6 per cent lower than the 16,569 in the same period last year. However, the Aedes mosquito population in October was double that in October last year.

NEA noted that warmer conditions caused by El Nino could result in shorter breeding periods for Aedes mosquitoes and shorter incubation times for the dengue virus.

"As a large proportion of our population is still susceptible to dengue infection due to the lack of immunity, an increase in the Aedes mosquito population and slightly warmer-than-usual weather could lead to a surge in dengue cases unless measures are taken to suppress the Aedes mosquito population," NEA said. It urged people to take measures to prevent mosquito breeding in and around their homes.

As of Tuesday, there were 48 dengue clusters.There were 284 cases of dengue in the week ended Nov 28, a slight increase from the 254 cases the week before.