SINGAPORE: Male Wolbachia-carrying mosquitoes will be released in more areas in Nee Soon East and Tampines West in November, as part of the next phase of a study to reduce the Aedes mosquito population and fight dengue.
Phase 3 of the study, conducted between February and October, had resulted in a more than 90 per cent drop in the urban Aedes aegypti mosquito population, said the National Environment Agency (NEA) on Monday (Oct 7).
This is an improvement from the 70 to 80 per cent drop seen in the second phase of the study.
Moving forward in phase 4 of the study, the release sites will be expanded to cover 163 residential blocks in Nee Soon East and 121 blocks in Tampines West, said NEA, nearly double the area in the previous phase.
Male mosquitoes infected with the Wolbachia bacterium do not bite or transmit diseases. When they mate with female Aedes mosquitoes, the eggs the females lay will not hatch.
In the fourth phase of the study, NEA will test the feasibility of using drones to release Wolbachia-carrying mosquitoes in some areas of the study sites.
Other automated solutions include a device that makes it easier to transport and release male Wolbachia-Aedes mosquitoes, as well as a sex-sorting technology that uses artificial intelligence (AI) to separate the males from the females.
Since 2012, NEA has been studying the effectiveness of the Wolbachia technology to suppress the urban mosquito population in Singapore.
“These have been the most comprehensive and exhaustive studies ever done, to determine how best to safely and effectively use this method in Singapore,” said Professor Duane Gubler, chairman of the Dengue Expert Advisory Panel (DEAP) and founding director of the Emerging Infectious Diseases Programme at Duke-NUS Medical School.
“We are optimistic that this method, when fully implemented, will tip the balance in favour of dengue control,” he said.
The results of the study so far demonstrate "the effectiveness of Wolbachia-Aedes technology in Singapore’s high-rise and high-density urban landscape", said NEA.
"Importantly, continued releases have kept the Aedes aegypti mosquito population at levels that pose low dengue risk," the agency added.
The population of Aedes aegypti mosquitoes is measured by the average number of caught in each Gravitrap in the area. According to NEA, numbers caught per trap have plunged from more than one to as low as 0.015 in some areas, since the release of Wolbachia-carrying mosquitoes.
Expanding the study sites in Nee Soon and Tampines will allow researchers to determine if this method of suppressing the Aedes aegypti mosquito population can be sustained in larger areas.
“The larger areas in Phase 4 will help us to demonstrate better efficacy, in other words, to achieve the same success with a smaller number of male Wolbachia-Aedes mosquitoes released at each block,” said Associate Professor Ng Lee Ching, director of NEA’s Environmental Health Institute.
Assoc Prof Ng said this would help to build a consistent and comprehensive dataset, and ensure that the study is robust before scaling it up to more areas beyond Yishun and Tampines.
WOLBACHIA NOT A SILVER BULLET
While the Wolbachia technology continues to show good results, NEA cautioned that it is not a silver bullet.
“Breeding of mosquitoes in the community will cancel out the positive impact of the technology,” said NEA, adding that the community must do its part to prevent and remove mosquito breeding habitats.
This way, fewer male Wolbachia-Aedes mosquitoes will need to be released for the technology to be successful, said NEA.