Parliament: 14,000 more mozzie traps to be deployed in next 4 months as dengue cases surge past 10,000

In this picture taken on March 19, 2014, a National Environment Agency officer shows how Aedes mosquitoes caught in the top part of the Gravitrap, where an adhesive layer is, are removed. PHOTO: ST FILE

SINGAPORE - The National Environment Agency (NEA) will progressively deploy another 14,000 Gravitraps, small black cylinders that trap female Aedes aegypti mosquitoes looking for water surfaces to lay their eggs, to new HDB blocks and landed estates over the next four months.

The additional Gravitraps will augment the NEA's current network of 50,000 traps, and enhance its surveillance capabilities, said Minister for the Environment and Water Resources Masagos Zulkifli in Parliament on Monday (Sept 2).

This will allow the NEA to prioritise its resources and deploy officers to focus on areas with a high mosquito population.

Mr Masagos was responding to questions by four MPs on the dengue situation.

There has been a surge in the number of dengue cases here, with 10,748 cases reported as of Aug 24, up from 9,135 in Aug 2.

Mr Masagos said that the rise in cases is attributable to three key factors: an increase in the mosquito population, the relatively warmer weather, and lower herd immunity in our population.

The Aedes aegypti mosquito population has increased almost three times since the last major dengue outbreak in 2013, which increases the risk of the transmission of dengue.

In addition, the mean temperature for the first half of this year was 0.7 deg C higher than the same period last year. Warmer temperatures result in the higher transmission of dengue due to the accelerated growth of the Aedes mosquito population and a shorter incubation period of the dengue virus.

Finally, due to Singapore's past successes in dengue prevention, the proportion of adults who have had dengue before has progressively decreased from 59 per cent in 2004 to 51 per cent in 2009 and 41 per cent in 2017.

This has resulted in lower herd immunity among the population here, and a large proportion of Singapore's resident population remains susceptible to dengue.

Mr Masagos highlighted a number of measures the NEA had taken to tackle the dengue issue.

He said that since Aug 25, the NEA has partnered the People's Association (PA) to step up dengue outreach efforts. Five thousand volunteers from PA grassroots organisations and the Community Emergency and Response Team will work with dengue prevention volunteers to conduct house visits and distribute dengue prevention leaflets.

The NEA has also taken to sharing information on areas with a relatively higher Aedes adult mosquito population on its webpage. This is to increase awareness of the risk of dengue in areas with a high mosquito population which might not yet be dengue clusters. This will enable stakeholders to pre-emptively take measures to reduce potential mosquito breeding habitats and prevent the formation of new dengue clusters.

Mr Masagos also addressed a question on whether his ministry would consider expediting the trial of Project Wolbachia, a scheme which involves the release of sterile male mosquitos, which results in the production of eggs that cannot hatch, in the top dengue clusters.

He emphasised that while results from field studies had shown promise, the technology had been tested only in small study sites in Singapore, and remains under research and development.

The project is now in its third phase, which aims to determine if the Aedes aegypti population suppression achieved thus far can be sustained in larger areas.

The current release area, which covers 84 blocks in Yishun and 60 blocks in Tampines, is 3.7 times larger than the release area when the project first started.

However, Mr Masagos said that, as field studies require prior systematic design, preparation and historical data for comparison, they are not suited for reacting to current dengue clusters, which are very dynamic.

He added that Wolbachia technology is "not a silver bullet" and will not replace community efforts, comprehensive mosquito surveillance, source eradication of mosquito breeding habitats, and spraying of insecticide where necessary to control the adult mosquito population.

Mr Masagos shared that the anti-dengue efforts so far have been paying off. As of Aug 24, 863 of the 1,021 dengue clusters formed this year had been closed. These include some of the largest clusters in Woodlands, Upper Thomson, Chai Chee and Pasir Ris.

The weekly number of dengue cases also came down from a high of 664 cases in the second week of July to the current 480 cases in the third week of August.

However, he added: "We are still in the peak dengue season, which stretches from June to October. The region around us is similarly seeing an upsurge in dengue cases this year. We need to remain vigilant, and continue to work as a community to suppress the Aedes mosquito population and keep dengue cases in check."

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