Singapore

Phase 2 of study to control dengue to start

There will be an added buzz in Tampines West and Nee Soon East come April with the release of male Wolbachia-carrying Aedes aegypti mosquitoes into the estates.

This is part of phase two of a field study into a novel method to curb dengue transmissions in Singapore which has delivered promising results.

The Aedes aegypti mosquitoes have been artificially infected with Wolbachia bacteria. When they mate with uninfected females, the resulting eggs will not hatch.

Phase two will involve more housing blocks. About one to six mosquitoes will be released per person each week, up from one to three mosquitoes.

Braddell Heights, which was part of the first phase, will not be involved this time as it does not have high-rise buildings - a focus of phase two.

These estates represent a cross-section of typical housing estates and have seen dengue outbreaks previously.

The National Environment Agency (NEA) has been monitoring the mosquito population in these sites for years, providing a baseline for comparative studies.

In phase one conducted from October 2016 to December last year, NEA found mosquito populations in the study sites were reduced by half.

The phase two study will run till January next year and aims to overcome challenges that cropped up in the earlier study, NEA said yesterday.

The agency said the plan was to embark on a larger suppression trial after phase one. But the first trial threw up unexpected hurdles.

Only 6 per cent of the adult male Wolbachia-carrying mosquitoes released at the ground floor were later found at the ninth floor level and higher.

So in phase two, the mosquitoes will be released at higher floors, in addition to being released at the ground floor.

They will also be released twice a week instead of once a week, in order to keep the population up for longer.

During phase one, the NEA noted that a small percentage of female Wolbachia-carrying Aedes aegypti mosquitoes were inadvertently released.

While normal female Aedes aegypti mosquitoes that mate with male Wolbachia-carrying mosquitoes lay eggs which do not hatch, female Wolbachia-carrying mosquitoes still go on to have offspring.

Hence all batches of Wolbachia-carrying mosquitoes, adult and pupae, will undergo X-ray treatment to ensure that any females present will be made infertile, before they are released into the study site.

Environment