NEA will be engaging residents and local stakeholders through house visits and block parties; members of the public are encouraged to find out more about Wolbachia technology

Singapore, 27 August 2016 - In April this year, the National Environment Agency (NEA) announced its intention to conduct further studies to determine the feasibility of releasing male Wolbachia-carrying Aedes aegypti mosquitoesto complement source reduction efforts to suppress the Aedes aegypti mosquito population in Singapore. Eggs produced from the mating between a male Wolbachia-carrying Aedes aegypti mosquito and a female urban Aedes aegypti mosquito (withoutWolbachia) will not hatch. Multiple releases of male Wolbachia-carrying Aedes aegypti mosquitoes over time will thus eventually lead to a reduced urban Aedes aegypti population, and reduce the potential spread of diseases such as dengue.

2          Following a comprehensive risk assessment of Wolbachia technology which has determined it to be safe, with no risk to human health and insignificant risk to ecology, NEA will be embarking on a six-month long small-scale field study from October this year to gain a further understanding of the behavior of male Wolbachia-carrying Aedes aegypti mosquito population in our urban environment.  

3          The small-scale field study involves the release of male Wolbachia-carrying Aedes aegypti mosquitoes on a regular basis at three selected sites located within Braddell Heights, Nee Soon East and Tampines West. Please see Annex A for the location maps of the three selected sites. These male Wolbachia-carrying Aedes aegypti mosquitoes do not bite or transmit diseases.

4          NEA will be engaging residents and local stakeholders in these sites in the coming weeks, through house visits and block parties. Members of the public are encouraged to find out more about Wolbachia technology.

5          Data collected from the small-scale field study will support the design of a subsequent suppression trial, in which releases of male Wolbachia-carrying Aedes aegypti mosquitoes will be optimised for effective suppression of the mosquito population. Ultimately, if the small-scale field study and the subsequent suppression trial are successful, NEA hopes to use Wolbachia technology to complement NEA’s existing vector control efforts and greatly reduce the spread of viruses such as dengue.

6          NEA emphasises that during all studies and trials exploring the potential of the Wolbachia technology, source eradication of mosquito breeding habitats and spraying of insecticide where necessary to control the adult mosquito population remain essential for dengue prevention In Singapore.

Studies on Various Novel Mosquito Control Methods

7          In spite of the low mosquito population in Singapore due to the eradication of mosquito breeding habitats, Singapore remains vulnerable to dengue outbreaks due to our location in a dengue endemic region and low herd immunity of the community. NEA regularly explores new tools and technologies to improve dengue control in Singapore. NEA’s Environmental Health Institute (EHI) has studied various novel mosquito control methods over the past six years, and has focused on the Wolbachia method over the last four years. Wolbachia’s potential to reduce the Aedes aegypti mosquito population has been demonstrated in our laboratories. The approach is based on the biology of Wolbachia-carrying insects, of which the eggs produced from the mating between a male Wolbachia-carrying Aedes aegypti and a female urban Aedesaegypti (without Wolbachia) will not hatch, and there will be no offspring. Multiple releases of male Wolbachia-carrying Aedes aegypti mosquitoes will thus lead to a reduction in the urban Aedes aegypti population over time. The Dengue Expert Advisory Panel (DEAP) has supported EHI’s study on Wolbachia, and will continue to review study results and guide experimental designs.

NEA’s Risk Assessment  

8          NEA has conducted a comprehensive risk assessment of Wolbachia technology and has determined it to be safe, with no risk to human health and insignificant risk to ecology. The conclusion is consistent with other international findings and the findings of an independent research company. NEA’s long evaluation process involved critical reviews of existing knowledge and research, and consultations with various stakeholders such as academic experts, medical and healthcare professionals and non-governmental organisations (NGOs).

9          With the comprehensive and meticulous laboratory studies completed to-date, NEA is now ready to embark on the small-scale field study. Professor Ary Hoffmann, an expert on Wolbachia-insect interaction, from the University of Melbourne in Australia, and DEAP member, said, “Wolbachia-carrying Aedes mosquitoes have been released in several places, such as Australia, China, Brazil, Indonesia and Vietnam, with no known negative impact on public health and ecology. This is consistent with our knowledge and assessment of Wolbachia, which is naturally present in other insects in the environment. We are satisfied with the results of NEA’s risk assessment and laboratory studies. We look forward to reviewing the results of the small-scale field study which will support the design of a subsequent suppression trial.”

Small-Scale Field Study

10        Field studies are necessary to demonstrate that the mosquitoes behave in the same way in the urban environment as they do in the laboratory. Male Wolbachia-carrying Aedes aegypti mosquitoes will be released at the three selected sites to help us understand how far and high they fly, how long they live and how well they compete with urban male mosquitoes for a mate. This data is required to support the design of a subsequent suppression trial, in which male Wolbachia-carrying Aedes aegypti mosquitoes will be released for further tests on their ability to reduce the mosquito population.

11        The three sites selected for the small-scale field study were based on a number of criteria:

• These sites represent a cross-section of typical housing estates in Singapore;
• These estates have seen dengue outbreaks previously and/or have Aedes aegypti mosquitoes present in the environment;
• NEA has been monitoring the mosquito population in these sites for up to three years, providing a baseline from which to make comparative studies

12        Grassroots Advisers and Leaders have given their support for the small-scale field study. Together with these Grassroots Advisers and Leaders, NEA will be engaging residents and stakeholders at the selected sites to inform them of the study and provide more information on Wolbachia technology and the small-scale field study, through outreach activities such as house-to-house visits and block parties. Residents will also be receiving educational materials and collateral on Wolbachia.

13        As male mosquitoes do not bite, the release of male Wolbachia-carrying Aedes aegypti mosquitoes will not pose any additional risk of biting or disease transmission. EHI estimates that an average of one to three male mosquitoes per person will be released regularly[1] at each of the selected sites over the six-month study period.

14        NEA researchers will be releasing the male mosquitoes at public spaces around houses and blocks. Release points may include stairwells, void decks, open spaces between blocks of high-rise homes, and outside landed homes from the streets. Mosquitoes will not be released directly into homes.

Collective Effort Needed to Fight Dengue

15        The co-operation and support from residents and local stakeholders at the selected sites will be crucial in ensuring the success of the small-scale field study. Residents do not have to do anything differently, but continue to carry out mosquito control procedures and practise the 5-Step Mozzie Wipeout as normal.

16        NEA researchers will be setting up three types of mosquito traps (Gravitraps, ovitraps and fan-based traps) at various locations, including public spaces and inside the homes of resident volunteers. We seek the co-operation of members of the public not to remove or tamper with the mosquito traps. Residents at the selected sites who wish to contribute to our research can do so by hosting fan-based mosquito traps in their homes and premises. NEA officers will regularly collect any mosquitoes caught in the traps for analysis. Resident volunteers will be compensated for the electricity used to power the fan-based traps. At the end of the study period, resident volunteers can retain the fan-based traps to continue catching mosquitoes in their homes. Residents at the selected sites who wish to contribute to our research or have any enquiries are welcome to contact NEA at 1800-CALL-NEA (1800-2255 632). Please see Annex B for images of the mosquito traps.

17        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, said: “The small-scale field study is an important and necessary step that NEA must take to understand how the male mosquitoes behave, which will support the design of a subsequent suppression trial. The suppression approach, when used in combination with other methods of control such as the current community-based removal of potential breeding habitats, and a vaccine when available, could be the key to a continued successful Singapore dengue control programme. While the Government studies this method, the cooperation and support from residents and local stakeholders at these selected sites, will be crucial in ensuring the success of the small-scale field study.”

18        Everyone must continue to play his part to help stem dengue transmission in the environment and reduce the mosquito population. NEA alone cannot eradicate Aedes mosquitoes. While NEA explores the potential of Wolbachiatechnology, source eradication of mosquito breeding habitats and spraying of insecticide to control the adult mosquito population remains essential for dengue prevention.

19        We encourage everyone to learn about Wolbachia technology, and share information on Wolbachia technology and the small-scale field study with their family and friends. If successful, Wolbachia technology has the potential to naturally contribute to dengue control in Singapore. Members of the public can find out more about Wolbachia technology by visiting www.nea.gov.sg or contact NEA at 1800-CALL-NEA (1800-2255 632) if they have any enquiries.

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 For more information, please contact us at 1800-CALL NEA (1800-2255 632) or submit your enquiries electronically via the Online Feedback Form or myENV mobile application.

ANNEX A

LOCATION MAPS OF THREE SELECTED SITES

Fig. 1 Location map of Tampines West site

Fig. 2 Location map of Braddell Heights site

Fig. 3 Location map of Nee Soon East site

ANNEX B

PICTURES OF MOSQUITO TRAPS

Fig 4 Traps that will be placed to monitor mosquito behaviour