Release of male Wolbachia-Aedes at a few selected sites seeks to understand behaviour of Wolbachia-Aedes in our environment

Singapore, 12 April 2016 –The National Environment Agency (NEA) has been conducting various studies and risk assessments to determine the feasibility of using Wolbachia-carrying male Aedes mosquitoes to suppress the Aedes aegyptimosquito population in Singapore. Having determined the efficacy and safety of this approach, as a next step, NEA plans to conduct a small-scale field study that involves the release of only male Wolbachia-Aedes at a few selected sites at the end of the year. The study seeks to understand the behaviour of Wolbachia-Aedes in our urban built-up environment, e.g. the longevity of Wolbachia-Aedes and the vertical and horizontal flight range of Wolbachia-Aedes in the open environment. This data is required to support the design of a subsequent suppression trial. More details of the small-scale field study will be announced when ready.

2          As male mosquitoes do not bite, the release of male Wolbachia-Aedes will not pose any risk of biting or disease transmission by the Wolbachia-Aedes. Wolbachia are naturally occurring bacteria found in over 60 per cent of insect species, including butterflies, fruit flies, dragonflies, and mosquito species such as Aedes albopictus, but not in the dengue-carrying Aedes aegypti mosquito.

Wolbachia Technology

3          On 18 March 2016, the World Health Organization (WHO) announced the WHO Vector Control Advisory Group (VCAG)’s recommendation on the use of Wolbachia-Aedes for limited pilot deployment under operational conditions, accompanied by rigorous monitoring and evaluation. Though the mentioned approach was referring to the replacement strategy that requires the release of both male and female Aedes aegypti mosquitoes, the recommendation supports the pilot release of Wolbachia-carrying mosquitoes.

4          NEA has been conducting a feasibility study on the use of Wolbachia-carrying male Aedes mosquitoes to suppress the Aedes aegypti mosquito population. The approach is based on the biology of Wolbachia-carrying insects, of which the eggs produced from the mating between a Wolbachia-carrying male Aedes aegypti mosquito and wild female Aedes aegypti mosquito (without Wolbachia) will not hatch.

5          NEA’s own comprehensive risk assessment is consistent with previous findings on the safety of Wolbachiatechnology. NEA has assessed that the technology has no or insignificant risk of negative impact on public health or the ecology. The Dengue Expert Advisory Panel (DEAP), appointed in June 2014, has supported the study, and continues to review study results and guide experimental designs obtained or developed by NEA’s Environmental Health Institute (EHI).

6          As part of the feasibility study on Wolbachia, NEA is also engaging relevant stakeholders and domain experts to enable a comprehensive study and assessment of the technology. In October 2015, NEA appointed a research company, to conduct an independent assessment to identify any potential secondary environmental and social impact that may arise from the implementation of the technology; and to identify appropriate mitigation and monitoring measures, to minimise and forewarn of any possible secondary consequences before, during and after implementation. NEA will provide updates on the study after it has been concluded in July 2016.

7          The information obtained from the various studies and from stakeholders will contribute to NEA’s studies on the use of Wolbachia technology as an additional dengue control tool.

Individual and Collective Efforts to Fight Dengue

8          While NEA explores new technologies such as the Wolbachia-carrying male Aedes mosquitoes, source eradication of mosquito breeding habitats by the community and all stakeholders remains the key to preventing dengue.

9          Community-led efforts are as important as NEA’s enforcement efforts in helping to reduce the mosquito population and stem dengue transmission. Source eradication of mosquito breeding habitats and spraying of insecticides to control the adult mosquito population remains the key to dengue prevention. Members of the community and stakeholders are urged to play their part to keep dengue cases down. NEA also works with the Town Councils, construction sites, foreign workers’ dormitories, People’s Association (PA) and grassroots organisations to spread dengue prevention messages.

10        There are currently 5,800 Dengue Prevention Volunteers (DPVs), comprising grassroots leaders, PA Community Emergency and Response Teams (CERT) members, students, senior citizens and residents, who help to educate residents on the 5-step Mozzie Wipeout (which includes inverting pails and plant pot plates, changing water in vases regularly, and capping bamboo pole holders) and the need to clear blockages in roof gutters and drains, and apply larvicide monthly. Additionally, more than 5,000 grassroots leaders and CERT volunteers will be trained to conduct house visits, with particular emphasis on homes in yellow and red dengue cluster areas.

Stepped-Up Vector Control Efforts 

11        NEA, together with the various agencies and stakeholders represented on the Inter-Agency Dengue Task Force (IADTF), including Town Councils, will continue to check and rid public areas and housing estates of potential mosquito breeding habitats daily through  space spraying, fogging, the oiling of drains and application of the Bacillus thuringiensis israelensis (BTI) larvicide.

12        As of 31 March 2016, NEA has conducted about 350,000 inspections islandwide and uncovered about 4,200 instances of mosquito breeding habitats. NEA has also issued 120 Notices to Attend Court (NTACs) and more than 20 Stop Work Orders (SWOs) to construction site contractors for mosquito breeding. More than 10 court prosecutions were taken against these contractors for repeat offences.

13        As the majority of the breeding sites are found in homes, such as in domestic containers and flower pot plates and trays, NEA has toughened its approach towards errant home owners. Previously, enforcement was taken against home owners when their place of residence is within a dengue cluster. Since 14 March 2016, NEA has extended its enforcement regime to all residences found with mosquito breeding, regardless of whether they are within or outside dengue cluster. In the first three months of 2016, more than 470 households were fined for breeding mosquitoes.

14        To enhance surveillance efforts, NEA’s Gravitrap surveillance programme has been extended with an increase in the number of traps deployed, from 4,000 traps to about 30,000 traps across 5,000 HDB blocks, and the data collected will guide source reduction efforts. Another 20,000 traps will be rolled out to the remaining 3,000 HDB blocks by June 2016. The data collected will provide lead indicators for more targeted preventive control in areas with higher mosquito population.

Dengue Situation in Singapore

15        Between January and March 2016, a total of 6,338 dengue cases were reported. This is 182 per cent higher compared to the same period in 2015, when 2,251 cases were reported. Unless immediate action is taken, the number of dengue cases in 2016 may exceed 30,000 – higher than the record in 2013 when 22,170 cases were reported. 

16        In March, we were encouraged to observe that there had been a 30 per cent reduction in mosquito population and an associated reduction in the weekly number of dengue cases. Despite the apparent reduction in the Aedes mosquito population and dengue cases, the threat of dengue remains. The number of weekly reported dengue cases is still high for this time of the year.

17        We need to press on as a community to further reduce the mosquito population, to prevent a rebound in the Aedesmosquito population and a sharp upturn of cases as the traditional dengue season approaches. 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.

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