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NEA to deploy bacteria-infected mosquitoes in fight against dengue

SINGAPORE — Male Aedes mosquitoes infected with a naturally-occurring bacteria that causes dud eggs when they mate will be released at a few selected sites at the end of this year in the first field study in Singapore on this biological control method’s effectiveness in suppressing the mosquito population.

An Aedes Aegypti mosquito larvae. AFP file photo

An Aedes Aegypti mosquito larvae. AFP file photo

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SINGAPORE — Male Aedes mosquitoes infected with a naturally-occurring bacteria that causes dud eggs when they mate will be released at a few selected sites at the end of this year in the first field study in Singapore on this biological control method’s effectiveness in suppressing the mosquito population.

Minister for the Environment and Water Resources Masagos Zulkifli announced the six-month study on Tuesday (April 12), which aims to get a clearer picture of how these Wolbachia-carrying mosquitoes survive in Singapore’s urban built-up environment and their vertical and horizontal flight range in the open environment.

Only male mosquitoes will be released for the study and as they do not bite, there is no risk of biting or disease transmission, said the National Environment Agency in a press release. Wolbachia is a naturally-occurring bacteria found in over 60 per cent of insect species, including butterflies, fruit flies, dragonflies, and certain mosquito species. The bacteria is, however, not found in the dengue-carrying Aedes aegypti mosquito.

Speaking during the debate on his ministry’s budget on Tuesday, Mr Masagos said, without disclosing the test locations: “We are not embarking on this lightly. We have studied this for years and have taken all steps to ensure that public health and safety will not be compromised.”

Nevertheless, a research company was appointed to carry out an independent assessment on whether the biological control method will pose any potential secondary environmental and social impact, and how to minimise these consequences. The study will conclude in July this year.

Injecting male Aedes with Wolbachia and releasing them as a way to suppress the species’ population has been around since the 1960s and has been tested in various countries, including Vietnam, Indonesia, Australia, and Brazil.

When an infected male mates with a female, the eggs do not hatch.

In Singapore, the authorities first announced it was considering the method in June 2014 and have so far conducted feasibility tests in laboratories, but not in the field. 

Mr Masagos said his ministry will engage residents and stakeholders to provide more information on the technology and study in due course.

The field study comes in the wake of a warning issued by the authorities in February that Singapore could have a historic high of 30,000 dengue cases this year because of the ongoing El Nino phenomenon, along with a change in the type of dengue virus circulating among Singapore’s population. The previous record was 22,170 dengue cases in 2013.

In the first three months this year, there were 6,338 dengue cases, which is more than double that during the same period last year. Although there was a 30 per cent reduction in mosquito population last month, leading to an associated reduction in the weekly number of dengue cases, Mr Masagos cautioned that Singapore is not in the clear, warning that the number of cases may yet climb during the traditional dengue season in June.

Among other efforts to tackle dengue, the NEA will train 5,000 more Dengue Prevention Volunteers this year, to nearly double the pool of 5,800 such individuals tasked with educating the public on riding breeding sites. The additional volunteers can boost house visit efforts, especially in yellow and red dengue cluster areas. Another 250 temporary officers will also be engaged by the NEA this year to carry out inspections islandwide.

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