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Wolbachia mosquito project to fight dengue expanded to Marine Parade construction sites, landed estate area

Wolbachia mosquito project to fight dengue expanded to Marine Parade construction sites, landed estate area

Field officers releasing male Wolbachia-Aedes mosquitoes using the mosquito launcher. (Photo: Facebook/Amy Khor)

SINGAPORE: A project to combat dengue in Singapore by releasing specially bred mosquitoes will be expanded to construction sites and the landed estate area in Marine Parade.

This is the first time such locations are being covered.

More HDB blocks in existing study sites such as Tampines and Yishun will also be included in the project, said the National Environment Agency (NEA) NEA on Monday (Jul 5).

The agency said it had been engaging residents at the Marine Parade landed estate area and recruited volunteers to host different mosquito traps in their homes for mosquito surveillance. 

From the fourth quarter of 2021, vans equipped with release automation technology will be deployed to conduct targeted small-scale releases of the male Wolbachia-Aedes mosquitoes at the area in Marine Parade. 

"Data gathered will help guide deployment for larger-scale releases at the (Marine Parade landed estate area)," said NEA. 

Releases will also be carried out at construction sites within the study sites, said NEA. The agency is working with relevant stakeholders, including construction companies, to guide them on the surveillance and release of the male Wolbachia-Aedes mosquitoes at such premises. 

READ: Higher risk of dengue transmission as Aedes mosquito population growing islandwide, says NEA

"This is part of our strategy to achieve better suppression at the study sites, by covering different terrains and landscapes," said NEA. 

NEA will also expand the project to cover existing study sites in Yishun, Tampines, Choa Chu Kang and Bukit Batok towns. 

Releases at Tampines and Yishun will gradually be expanded to cover 686 and 769 HDB blocks respectively, with about 60 per cent of the blocks covered as of May 1, 2021. High-risk areas within Choa Chu Kang and Bukit Batok towns will also be covered by the end of 2021. 

Associate Professor Ng Lee Ching, group director of NEA's Environmental Health Institute said the "overall positive impact" of Project Wolbachia is "very encouraging". 

"This is the first time that the technology has been shown to be effective in suppressing Aedes mosquitoes and reducing dengue in a challenging tropical highly-urbanised and high-rise environment," said Assoc Prof Ng. 

88% FEWER DENGUE CASES AT EXISTING STUDY SITES

Up to 98 per cent suppression of the populations of this dengue vector was observed at the core of the study sites, with a positive spillover effect also observed at non-release areas next to the release sites. 

Core areas of the study sites with at least one year of releases saw up to 88 per cent fewer dengue cases, compared to those areas without releases, said NEA. 

As of June 2021, releases of the male Wolbachia-Aedes mosquitoes at Yishun and Tampines have been expanded, from 39 HDB blocks to 860 HDB blocks across both towns. 

READ: Not pests, but sources of information: A mosquito analyst's work in the fight against dengue

Releases are also ongoing at dengue high-risk neighbourhoods at Choa Chu Kang and Bukit Batok, covering 207 HDB blocks where there have been consistently high Aedes aegypti mosquito populations.

The "positive outcome" of the field studies at Tampines and Yishun show that continued releases of the male Wolbachia mosquitoes can successfully suppress the female Aedes aegypti mosquito population in Singapore, said NEA. 

In most areas within the study sites, one to nine mosquitoes were caught per 100 traps per week after a few months of releases, significantly below the 50 or more mosquitoes caught prior to the releases. 

Recent data from Choa Chu Kang and Bukit Batok also showed a similar reduction in the Aedes aegypti mosquito populations, with most areas having fewer than 10 mosquitoes caught per 100 traps per week. 

MOST AREAS SHOWED "GOOD SUPPRESSION" OF AEDES AEGYPTI MOSQUITO POPULATION

Most areas in the study sites showed "good suppression" of the Aedes Aegypti mosquito population within three to four months of the beginning releases, said NEA. 

However, there was dengue transmission in a few areas where it took longer to reduce the mosquito population. 

READ: Tool kits to prevent mosquito breeding to be given to about 75,000 landed homes, as dengue cases remain high

In parts of Tampines East and Changkat, the start of the releases coincided with a general spike in the mosquito population in May 2020. This suggested that environmental factors can delay suppression. 

Some of these areas were also adjacent to non-release areas with persistently high populations of the Aedes aegypti mosquito or existing large dengue clusters. These contributed to dengue transmission within the study sites, from September to December 2020. 

The Aedes aegypti mosquito populations were eventually suppressed to lower levels in February 2021. 

The study also showed that in areas with very low Aedes aegypti mosquito populations, the presence of female Wolbachia-Aedes mosquitoes could result in Wolbachia-Aedes mosquitoes propagating in the field.

The eggs from a pair of mated Wolbachia-Aedes mosquitoes are viable and can hatch, which result in Wolbachia-carrying offspring, said NEA. 

An increase in the female Wolbachia-Aedes mosquito population was observed at a small section of the Tampines West study area in June 2020. The Aedes aegypti mosquito population had previously been reduced to very low levels by Project Wolbachia. 

READ: Residents in landed estates at higher risk of getting dengue as cases remain high: NEA

The female Wolbachia-Aedes mosquitoes in the community are "less harmful" than urban Aedes aegypti mosquitoes, as they are partially resistant to dengue infection and do not transmit dengue well, said NEA. 

X-ray irradiation, which uses photon radiation, was also introduced to sterilise the male Wolbachia-Aedes mosquitoes, which reduced the urban Wolbachia-Aedes mosquito population. 

Dengue expert advisory panel chairman Professor Duane Gubler said NEA's progress in implementing Project Wolbachia in the past five years has been "outstanding".

"The rigorous research and excellent data from these pioneering studies are critical to effectively scale up the programme, not only in Singapore, but also in other dengue endemic countries," said Prof Gubler.

READ: Why the dengue fever caseload has plummeted in parts of Southeast Asia this year

As of Jun 28, there are 35 active dengue clusters in Singapore, according to the NEA website. Large clusters are located at Cashew Terrace, Hazel Park Terrace, Balmoral Park and Tuas South Boulevard. 

Singapore has reported a total of 3,275 dengue cases for 2021. 

Source: CNA/lk(ac)

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