NEA will review Panel’s recommendations, and continue working with relevant experts and stakeholders to ensure safe and effective use of Wolbachia technology

Singapore, 17 October 2014 – The Dengue Expert Advisory Panel, comprising experts from Singapore, Australia, the United Kingdom (UK) and the United States of America (USA), recommends that Singapore explores the use of Wolbachia-carrying Aedes males to help suppress the Aedes mosquito population in Singapore, for further reduction of the risk of dengue[1]. The Panel emphasised that the implementation of such new tools should not preclude continuation of the ongoing surveillance and mosquito control efforts. Appointed by the National Environment Agency (NEA) in June 2014, the Panel concluded that the proposed approach holds promise for Singapore and field trials are needed to prove its feasibility and effectiveness. NEA will review the details of the recommendations, and continue working with relevant domain experts and stakeholders to develop the framework for the safe and effective adoption of Wolbachia technology (see Annex A for facts on Wolbachia technology).

2          The Dengue Expert Advisory Panel (see Annex B for list of members), with specialised knowledge on vector-borne diseases, entomology, epidemiology, virology and public health, met for the first time from 13 to 16 October 2014. The Panel reviewed the latest scientific literature underlying these new modalities, Singapore’s dengue epidemiology, and data derived from the multi-disciplinary studies conducted at NEA’s Environmental Health Institute (EHI). Taking local epidemiology and ecology into consideration, the Panel evaluated the safety and effectiveness of using these new methods in our local context.

3          “Wolbachia-carrying Aedes has been released in several places, such as Australia, Brazil, Indonesia and Vietnam, with no negative impact on public health and ecology. This is consistent with our knowledge and assessment. Wolbachia provides a safe strategy, because the bacteria are naturally present in a large fraction of insects. Organisms in the natural environment have been continuously exposed to Wolbachia for millions of years,” explained Professor Ary Hoffmann, an expert on Wolbachia-insect interaction, from the University of Melbourne in Australia. Male mosquitoes do not bite or transmit disease, and Wolbachia are naturally occurring bacteria (non-genetically modified) found in more than 60 per cent of insect species.

4          The Panel agreed to the additional laboratory and cage studies proposed, to further understand Aedes population dynamics and improve mosquito rearing techniques. In addition, the experts recommended further studies, entailing the field release of Wolbachia-carrying Aedes males. These studies aim to demonstrate that the Wolbachia-carrying Aedes males are able to suppress the local Aedes population.

5          This suppression approach is consistent with our current emphasis on source reduction of the Aedes mosquito. This approach is especially useful in controlling mosquitoes that are breeding in hidden habitats that cannot be reached by current methods. The Panel also recommended that Singapore remain open to considering other novel technologies available.

6          While NEA explores the potential of Wolbachia technology, source eradication of mosquito breeding habitats remains key to preventing mosquito breeding. All stakeholders must continue to play their part to help stem dengue transmission in the environment, by checking their premises daily for potential mosquito breeding habitats and removing them. Those infected with dengue should protect themselves from mosquito bites by applying repellent as regularly as possible, and those showing symptoms suggestive of dengue, should see their GPs early to be diagnosed.

7          Professor Duane Gubler, Chairman of the Dengue Expert Advisory Panel, and Founding Director of the Emerging Infectious Diseases Program at Duke-NUS Graduate Medical School, added: “The approach with Wolbachia-carrying Aedes males will likely be most effective 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. Because of differing ecology, epidemiology and demographics, each country will have to develop a strategy that is most appropriate for the local situation. Singapore, with its comprehensive dengue surveillance and control system, coupled with a strong research culture, is an ideal place to assess this approach in the context of its existing dengue control programme.”

8          NEA noted and expressed appreciation for the Panel’s recommendations.

– End –

[1]Aedes aegypti in our environment does not carry Wolbachia. These wild-type females will produce eggs that do not hatch when they mate with Wolbachia-carrying Aedes males introduced into the environment. The production of non-viable eggs is expected to result in a reduction of the mosquito population in the environment.

ANNEX A

FACTSHEET ON WOLBACHIA TECHNOLOGY

Wolbachia Technology

• Wolbachia is a naturally occurring bacterium found in more than 60 per cent of insect species. In our environment, Aedes aegypti – the primary dengue vector – does not carry Wolbachia. Wolbachia-carrying Aedes aegypti male mosquitoes, when mated with Aedes aegypti female mosquitoes, produce eggs that do not hatch. This form of ‘sterility’ is due to a phenomenon known as ‘cytoplasmic incompatibility (CI)’.

• The use of such Wolbachia-carrying Aedes aegypti males to compete with wild-type males for wild-type females can theoretically lead to a reduction in the mosquito population. The ultimate goal is suppression of the Aedes population to a level that cannot sustain dengue transmission.

• The use of Wolbachia-carrying male mosquitoes for mosquito control is not new.

The use of Wolbachia-carrying male mosquitoes for mosquito population control is not new. A pilot study sponsored by the World Health Organization (WHO) in Myanmar in 1967, showed that the release of non-native Wolbachia-carrying Culex quinquefasciatus males led to a zero per cent hatch rate of mosquito eggs by the twelfth week. Such a strategy has also been successfully trialled in a Pacific Island in 2009, for suppression of the Aedes polynesiensis mosquito population.

• In addition, field trials involving the release of Wolbachia-carrying mosquitoes have been conducted since 2012. International field releases of Wolbachia-carrying Aedes aegypti have been carried out in other countries, after comprehensive risk assessments ascertained that the technology was safe to be used.

EHI’s Studies on Wolbachia Technology

• NEA’s Environmental Health Institute (EHI) has been carrying out various laboratory research studies to confirm that the desirable properties of Wolbachia are retained when they are transferred to local strain of Aedes aegypti:

a.    Cytoplasmic incompatibility

Preliminary data from EHI’s laboratory studies show that mating between Aedes aegypti males carrying Wolbachia, and wild-type Aedes aegypti females, results in no mosquito progeny due to cytoplasmic incompatibiilty. Additional experiments under different environmental conditions suggest that Wolbachia-carrying Aedes aegypti males are “sterile” when they mate with mosquitoes in the field and could reduce the mosquito population.

b.    Reduction in capacity to transmit dengue and chikungunya infection

EHI has been studying the dengue and chikungunya-blocking abilities conferred to Aedes aegypti by Wolbachia. This was done by introducing viruses into Aedes aegypti females in the laboratory. Results show that Wolbachia-carrying mosquitoes have a lower transmission potential for all dengue serotypes, as well as for chikungunya, compared to non-Wolbachia carrying mosquitoes.

c.    Competitiveness of Wolbachia-carrying Aedes aegypti males with wild-type males

Preliminary data from EHI suggest that, under laboratory conditions, Wolbachia-carrying Aedes aegypti males are able to compete with wild-type male mosquitoes for mating. Data shows that Wolbachia-carrying Aedes aegypti males in the field could compete with males in the field for the Aedes aegypti females in the field.

• To ensure that the use of such technology to control dengue is safe, a Dengue Expert Advisory Panel was appointed in June 2014 to provide professional advice to NEA on such new modalities for dengue control, particularly on the use of Wolbachia for the suppression of the Aedes population. The panel consists of both local and international experts, with multi-disciplinary specialised knowledge on vector-borne disease, including entomology, epidemiology, virology and public health, and will assess the suitability of using Wolbachia-carrying Aedes aegypti males for reducing the impact of dengue in Singapore.

Stepped-Up Efforts by Government

• NEA, together with the other Government agencies from the Inter-Agency Dengue Task Force (IADTF), as well as Town Councils, are continuing to check public areas and housing estates for potential breeding grounds, with officers carrying out daily checks for breeding habitats in these areas. We are also eliminating adult mosquitoes through measures such as space spraying and deploying Gravitraps.

• NEA has conducted about two million inspections this year and we will continue to place emphasis on checking areas that have higher potential for dengue transmission, such as construction sites.

• NEA has stepped up its inspection efforts on construction sites since last year. This year, we have issued 598 Notices to Attend Court and 71 Stop Work Orders, and 14 contractors have been prosecuted in court for repeat offences as of 20 August 2014. We will continue to prosecute recalcitrant errant contractors and press for deterrent sentences.

ANNEX B

FACTSHEET ON THE DENGUE EXPERT ADVISORY PANEL

• To ensure that the use of such technology to control dengue is safe, NEA has recently appointed a Dengue Expert Advisory Panel to provide professional advice on new modalities for dengue control, particularly on the use of Wolbachia for suppression of the Aedes population.

• The roles of the panel are to:

1. Review latest scientific literature on dengue infection, with particular emphasis on risk factors and identifying new modalities for disease control;
2. Advise NEA on the planning, experimental design and implementation of appropriate interventional studies;
3. Assess the suitability of using Wolbachia-carrying Aedes males for reducing the impact of dengue in Singapore, taking local epidemiology and ecology into consideration.

• The multi-disciplinary panel comprises both local and international experts, with specialised knowledge on vector-borne diseases, entomology, epidemiology, virology and public health. The composition of the panel is: