NEA to test novel way of cutting mosquito numbers

Study using bacteria-infected male mozzies to render females sterile to be held in three areas

Hands being placed in a box of Wolbachia-carrying mosquitoes to demonstrate that they do not bite.
Hands being placed in a box of Wolbachia-carrying mosquitoes to demonstrate that they do not bite. ST PHOTO: CHEW SENG KIM

From October, some residents might notice more mosquitoes buzzing in their neighbourhoods.

But don't worry, they won't bite.

In fact, these male Aedes mosquitoes do not transmit disease, but are Singapore's latest allies in the fight against dengue. What the male mosquitoes will be armed with is Wolbachia, a naturally occurring bacterium. When these males mate with female mosquitoes, the bacterium causes the females to lay eggs that do not hatch.

Over time, this could lead to a fall in the population of Aedes aegypti mosquitoes, which transmit the viruses that cause dengue fever. These mosquitoes also carry the chikungunya and Zika viruses.

Yesterday, Environment and Water Resources Minister Masagos Zulkifli announced that the National Environment Agency (NEA) will release the bacteria-carrying mosquitoes at three sites as part of a field study. The areas, Yishun Street 21, Tampines Avenue 4 and Jalan Riang/Jalan Sukachita in Braddell Heights, previously had dengue outbreaks and represent a cross-section of typical housing estates here - both high-rise and landed.

The Environmental Health Institute, a public health laboratory at the NEA, has been studying this novel method since 2012 and carrying out risk assessment and research to confirm that it is safe.

  • Frequently asked questions about Wolbachia

  • Q Why is the National Environment Agency (NEA) conducting a field study that involves the release of male Wolbachia-carrying Aedes aegypti mosquitoes?

    A Such mosquitoes can potentially reduce the Aedes aegypti population, which spreads dengue.

    When they mate with their female counterparts, it results in eggs that do not hatch and no offspring.

    The field study is needed to ensure this strategy will work in our urban environment.

    Q Is anew mosquito species introduced into the environment?

    A No. The male Wolbachia-carrying Aedes aegypti mosquito is from the same species as the one in our environment. The only difference is that it is carrying Wolbachia, a naturally-occurring bacterium found in 60 per cent of insect species.

    Q How safe is Wolbachia?

    A NEA has conducted a comprehensive risk assessment of the method and found it to be safe, with no risk to human health and insignificant risk to ecology.

    Q Why were the three sites - within Braddell Heights, Nee Soon East and Tampines West - chosen for the field study?

    A They represent a cross-section of typical housing estates and have seen dengue outbreaks previously and/or have Aedes aegypti mosquitoes present. NEA has been monitoring the mosquito population in these sites for up to three years, providing a baseline for comparative studies.

    Q Will residents at the sites get more bites?

    A They may see a temporary increase in mosquitoes in the first few days after each release. Male mosquitoes may land on humans as they are seeking a mate, which is likely to be near a human, in search ofa meal.Butmalemosquitoesdonot bite or transmit diseases as they feedonplant juices.

    Q Dothe male mosquitoes draw female ones to the sites?

    A No, the male mosquito is attracted to the female, not the otherwayround. Source: NEA

Mr Masagos told reporters that while efforts to reduce the mosquito population have been "fairly successful", Singapore is still susceptible to dengue outbreaks as it is in a region where dengue is endemic.

He said the new method "works together with source eradication". "Whatever we're doing today to ensure that mosquitoes don't have opportunity to breed must continue."

The NEA estimated that an average of one to three male mosquitoes per person will be released at regular intervals at each of the three sites.

The six-month field study aims to understand the behaviour of Wolbachia-carrying Aedes aegypti male mosquitoes in the urban environment, such as how far and high they fly, and how well they compete with counterparts without Wolbachia to mate with females.

To collect data, NEA will set up traps at locations including public spaces and the homes of resident volunteers. The data will support the planning for a suppression trial, which may start next year.

Experts said that similar trials abroad have had a positive impact.

For instance, a release of Wolbachia-infected mosquitoes led to a more than 90 per cent drop in the mosquito population on an island in Guangzhou, China, under a pilot project starting in March last year.

Professor Ary Hoffmann from the University of Melbourne, who sits on the Dengue Expert Advisory Panel appointed by NEA in 2014, said: "Sterile release has been used against disease vectors and agricultural pests very successfully for many years around the world.

"The only difference here is that sterility is being generated through Wolbachia rather than radiation, but Wolbachia bacteria are already present in many insects...and do not pose any risk to humans."

He added that Wolbachia, which can be found in over 60 per cent of insect species including butterflies and dragonflies, cannot be transmitted to mammals, including humans, as the bacteria cannot survive outside insect cells.

Mr Derek Ho, director-general of NEA's Environmental Public Health Division, said residents should continue mosquito-control procedures, such as clearing stagnant water. Associate Professor Vernon Lee, of the National University of Singapore's Saw Swee Hock School of Public Health, said: "Any gains through the Wolbachia method could be negated if residents provide mosquitoes with an abundance of breeding sites."

Housewife Winnie Lim, 49, who lives at one of the Tampines blocks where the field study will be conducted, said the Wolbachia technology sounds like a "good idea".

"Instead of fumigating all the time, this is a long-term effort to wipe out the mosquitoes."

A version of this article appeared in the print edition of The Sunday Times on August 28, 2016, with the headline 'NEA to test novel way of cutting mosquito numbers'. Subscribe