Early data from small-scale field study indicates that released male Wolbachia-Aedes mosquitoes will reduce fertility of urban Aedes aegypti females

Singapore, 8 February 2017 – The Project Wolbachia–Singapore small-scale field study has yielded valuable data to help guide the next phase of trials. This was a key conclusion that the National Environment Agency's (NEA) Dengue Expert Advisory Panel arrived at after a three-day meeting with researchers from NEA’s Environmental Health Institute (EHI) to review the data collected from the study. The Panel strongly supported building on the good progress of the small-scale field study, and collecting more data over the next few months to refine the design of the larger suppression trial planned for later this year. The proposed suppression trial will test the utility and effectiveness of this approach in suppressing the urban Aedes aegypti mosquito population.

Background on Project Wolbachia–Singapore 

2          Project Wolbachia–Singapore is evaluating the use of male Wolbachia-Aedes mosquitoes to further suppress urban Aedes aegypti mosquitoes in the community. When these released male Wolbachia-Aedes mosquitoes mate with urban females in the community, the resultant eggs do not hatch. The continual release of male Wolbachia-Aedes mosquitoes is thus expected to reduce the hatchability of the Aedes eggs, and hence bring about a gradual reduction in the urban Aedes aegypti mosquito population. The small-scale field study was launched in 2016, involving releases of male Wolbachia-Aedesmosquitoes to test various parameters and pave the way for further trials that would be necessary before actual field deployment of this new technology. After extensive engagement with the residents and other stakeholders, the small-scale field study is being conducted at three selected sites at Braddell Heights, Tampines West and Nee Soon East.

Key Findings of Small-Scale Field Study

3            Following three months of releases at the Tampines West site, the viability of Aedes mosquito eggs collected from the site has been reduced by about half, suggesting that the released male Wolbachia-Aedes mosquitoes successfully mated with the urban Aedes aegypti females. The investigations at the other two sites (Braddell Heights and Nee Soon East) focused mainly on understanding the mate-seeking behaviour and flight ability of the released male Wolbachia-Aedesmosquitoes, as well as their survivability in the urban environment. The field studies to-date have provided much valuable ecological information on the behaviour of mosquitoes in Singapore. The valuable data collected by NEA at all three sites will help guide the design of the planned suppression trial. Whilst more data is being collected from the field study to further refine the trial design, the preliminary results can be found on the NEA website[1]. NEA appreciates the strong support from the community for the project, and is especially grateful to the volunteers who have participated in the hosting of traps for collection of data. 

The Dengue Expert Advisory Panel's Activities and Endorsements

4          The Panel (see Annex A for list of members), comprising experts from Australia, Singapore, the United Kingdom and the United States of America, with specialised knowledge on vector-borne diseases, entomology, epidemiology, virology and public health, met from 6 to 8 February 2017. In addition to reviewing the extensive data set collected by EHI researchers, the Panel visited EHI’s mosquito production facility at Neythal Road to observe the production and quality control of Wolbachia-Aedes mosquitoes. The Panel also visited the Braddell Heights, Tampines West and Nee Soon East study sites, where traps have been deployed and data collection is ongoing.

5          The Panel noted that NEA had assembled a strong team of scientists to plan and conduct these trials, and endorsed the use of Wolbachia-Aedes technology to complement Singapore’s Aedes mosquito control programme. The Panel was pleased with the success achieved so far, including the production process to reliably supply the Wolbachia-Aedesmosquitoes, and was also impressed with the high level of community engagement carried out and the support obtained.

6          Professor Neil Ferguson, Founding Director of the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London, and Director of the Health Protection Research Unit for Modelling Methodology under the United Kingdom National Institute for Health Research said, “It is an exciting time for dengue control in Singapore. Building on its already impressive record of vector control, NEA’s development of Wolbachia as a new technology to suppress Aedes aegypti populations offers the potential to dramatically reduce dengue and Zika transmission in future. The field trials currently underway are collecting the data needed for a rigorous scientific assessment of the effectiveness of this innovative approach.”

7          Besides being an efficient vector of the dengue virus, Aedes aegypti is also a primary vector of the Zika virus, which caused an outbreak in Singapore in August 2016. A successful Wolbachia-Aedes control technology would become an additional tool in the fight against not just dengue, but other diseases transmitted by Aedes aegypti, such as chikungunya, Zika and Yellow Fever.

8          Professor Duane Gubler, Chairman of the Dengue Expert Advisory Panel, and Founding Director of the Emerging Infectious Diseases Programme at Duke-NUS Medical School said, “NEA and the people of Singapore are to be congratulated on the rapid containment of what could have been a major Zika epidemic here. Singapore’s holistic approach to controlling Aedes-transmitted diseases, involving intensified active surveillance, intensified adult and larval mosquito control, community outreach and clinical management, can serve as a model for other countries affected by these diseases.”

9          Whilst the Wolbachia-Aedes technology holds much promise as an additional tool for Aedes control, we should not rely on it as our sole strategy. A strong integrated vector control programme with community participation, underpinned by Singapore’s  well-established programme for elimination of mosquito breeding habitats and selective use of insecticides where necessary to control the adult mosquito population, remain essential for dengue prevention in Singapore. NEA urges everyone to continue to remain vigilant and practise the 5-step Mozzie Wipeout. Persons infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see their doctors early to be diagnosed. The latest updates on the dengue situation can be found at the Stop Dengue Now Facebook page, www.dengue.gov.sg or the myENV app.