​Singapore is considering field tests using special mosquitoes that could help keep the population of the dengue-spreaders in check, as part of efforts to find new ways to fight the disease.

Last year, the National Environment Agency's (NEA) Environmental Health Institute began doing laboratory tests of male Aedes aegypti mosquitoes infected with Wolbachia bacteria. Aedes aegypti is the main culprit behind dengue. 

Wild female mosquitoes lay sterile eggs if mated with Wolbachia-carrying males.   The NEA's tests showed that this is true for the local strain of Aedes aegypti mosquitoes, and that males with Wolbachia are able to compete with wild males here for mates.

Lab tests have been completed and a panel of experts will review the research and decide if field tests should be done, said Second Minister for the Environment and Water Resources Grace Fu yesterday, at the launch of the nationwide "Do the Mozzie Wipeout" campaign in Bukit Panjang.

The use of mosquitoes infected with Wolbachia, which have no effect on humans, has been field tested in Australia, Vietnam and Indonesia.   But there are no plans yet to use these bugs on a large scale here. "Besides the main strategy of source eradication, we're always exploring new technology or methods," Ms Fu said.   For instance, the NEA has used a device called a gravitrap since 2012 to lure and trap adult mosquitoes.

Potential ecological effects of releasing Wolbachia-carrying males are unlikely, NEA said, as the bacteria are naturally present in 60 per cent of insects, including butterflies, cockroaches and Culex mosquitoes.

The panel of experts studying the research comprise Duke-NUS epidemiologist Duane Gubler, Singapore Armed Forces biodefence centre head Vernon Lee, Tan Tock Seng Hospital clinical microbiologist Tim Barkham and three others from the US, Britain and Australia. They will meet in August.

Ms Fu said that as at June 7, about 7,000 dengue cases have been reported this year.   While this is fewer than during the same period last year, "the level is still too high", she said.   Cases have been rising in recent weeks, and the months from June to October tend to have higher rates because mosquitoes breed faster and the dengue virus multiplies more rapidly in these warmer months.

She urged residents to take preventive measures such as capping bamboo pole holders when they are not in use, and covering toilets when they travel overseas.

Source: The Straits Times, Singapore Press Holdings Limited. Reproduced with permission.