SINGAPORE, Jun 15, 2022, TODAY. The authorities will be expanding a flagship project to reduce the Aedes mosquito population to cover about a third of Housing and Development Board (HDB) flats here from July as dengue cases keep soaring towards record levels, Malay Mail reported.
With this latest expansion, Project Wolbachia will cover another 1,400 blocks of HDB flats, adding up to 31 per cent of HDB blocks or 300,000 homes in total, said the National Environment Agency today.
NEA’s announcement comes as the number of dengue cases here continues to soar, with more than 14,000 dengue cases reported so far this year, more than double the total 5,258 dengue cases reported in 2021.
Minister for Sustainability and the Environment Grace Fu warned on Wednesday at the fifth Asia Dengue Summit held here that weekly local cases may very well surpass the record of 1,800 set in 2020, possibly even surpassing 2,000.
However, Fu added that the Wolbachia technology is not a “silver bullet” to control the disease.
Piloted in 2016, the project involves releasing male Aedes aegypti mosquitoes infected with the parasitic microble Wolbachia at test sites.
Eggs laid by female mosquitoes that mate with these Wolbachia-Aedes males will be sterile and will not hatch, hence reducing the population numbers for these mosquitoes — the main vector for dengue here.
Eight new sites including Choa Chu Kang, Sengkang and Geylang NEA said that Wolbachia-Aedes male mosquitoes will be released at eight new locations: Bedok North, Bedok Reservoir, Choa Chu Kang (Yew Tee), Geylang, Hougang, Punggol, Sengkang and Woodlands.
Releases will also take place at selected construction sites and non-residential sites in dengue high-risk areas.
The expansion of the project is expected to suppress mosquito populations at the locations while providing data to determine the impact of the technology on dengue cases and clusters.
According to NEA, the sites were selected based on a set of criteria – the historical dengue risk level, the Aedes aegypti population, the size and landscape of the area, and the agency’s capacity for producing and releasing male Wolbachia-Aedes mosquitoes.
The project has shown success at some sites, such as those in Tampines and Yishun, where more than one year of mosquito releases have been conducted.
NEA said it has previously observed a 98 per cent reduction in the dengue mosquito population and up to 88 per cent reduction of dengue cases at these two areas.
“Similar observations have been made in the current dengue outbreak where these areas have 70 per cent less dengue cases compared to similar areas without Wolbachia,” the agency added.
To support the expansion of this project, the Government will be ramping up its production of male Wolbachia-Aedes mosquitoes from two million per week currently to five million by the end of year.
Dengue ‘impossible to eradicate’: expert Despite the success shown in some test sites, overall dengue cases have been steadily on the rise.
In 2020, Singapore experienced its worst dengue outbreaks, with more than 35,000 cases and 32 deaths.
“In 2022, we are once again in the midst of an outbreak: More than 14,000 cases have been reported to date, with an earlier-than-usual surge in dengue cases that began in March,” said Fu.
Weekly cases could surpass the 2,000-mark as this is only the beginning of the traditional peak dengue season from June to October, she added.
TODAY has asked NEA why this continues to be the case despite Project Wolbachia currently covering one in five public housing flats, before the upcoming expansion.
Other questions submitted to the agency are: Why some existing test sites still show up as red or yellow alert high-risk areas in its dengue map, and to what extent case numbers are expected to decline as the initiative is rolled out to more places.
NEA has not yet responded to the questions.
In a section of its website dealing with frequently asked questions, the agency said that dengue cases reported within study sites could be due to the “presence of low-level dengue transmissions” or because those areas were infected areas.
Nonetheless, “significantly fewer” dengue cases were recorded in study sites compared to areas without releases, it said.
Regarding the high number of dengue cases in 2020 despite the roll-out of Project Wolbachia, NEA said on the website that study sites back then were still relatively limited in scale, covering only about 8 per cent of all HDB blocks.
“Though the number of dengue cases were significantly reduced within the release sites, they were not expected to significantly impact the dengue outbreak in 2020,” said NEA.
Associate Professor Koh Tieh Yong, weather and climate scientist at Singapore University of Social Sciences, told TODAY that the successful reduction of dengue cases in the study areas is “already quite an achievement”.
He also pointed to Singapore’s equatorial climate that favours mosquito breeding and the dense population here.
“Both factors make mosquito-transmitted diseases like dengue almost impossible to eradicate,” he said.
Professor Duane Gubler, Dengue Expert Advisory Panel Chairman and Emeritus Professor at Duke-NUS Medical School, Singapore, said that while studies have shown promise, Project Wolbachia alone will not be sufficient to control the dengue situation in Singapore.
Fu in her speech today said that studies have shown that the impact of Wolbachia technology is maximised when coupled with existing community efforts and vector control operations to suppress the presence of breeding habitats.
“Ultimately, individual and community responsibility and actions are still the most critical elements of dengue control,” said the minister.