NEA to release bacteria-carrying mosquitoes in former clusters to fight dengue

Loke Kok Fai Channel NewsAsia 27 Aug 16;

SINGAPORE: Thousands of male Aedes aegypti mosquitoes carrying the Wolbachia bacterium will be released regularly into three former dengue clusters at Tampines Avenue 4, Yishun Street 21, as well as Jalan Riang and Jalan Sukachita in Serangoon over six months from October 2016, the National Environment Agency (NEA) announced on Saturday (Aug 27). It is part of a "small-scale" field study and comes after a comprehensive risk assessment found it would be safe to release such mosquitoes, with no risk to human health and insignificant impact on ecology, NEA said.


Only female Aedes mosquitoes spread dengue by biting humans. Should a male carrier of the Wolbachia bacterium mate with an uninfected female mosquito, the resulting eggs will not hatch. NEA hopes that by releasing sufficient numbers of Wolbachia-carrying Aedes aegypti males, they can compete successfully against wild males and eventually drive down mosquito numbers as the population fails to reproduce. Over time, this could also reduce the potential spread of dengue. NEA expects that the method could also help prevent the transmission of other mosquito-transmitted diseases such as Chikungunya and Zika.

NEA said it carried out a four-year evaluation of the process, involving critical reviews of existing research, consultations with various stakeholders such as academic experts, medical and healthcare professionals, and non-governmental organisations such as nature groups. It found the bacterium – which is naturally found in insects in the wild – to offer suitable biological properties

The field study will observe how far the mosquitoes are able to disperse outside the lab, as well as how high they can fly. It will also gauge their lifespans in the wild, and how well they can compete for mates. An average of one to three mosquitoes per resident will be released regularly in areas such as stairwells, void decks, open spaces between blocks of high-rise homes, and outside landed homes of the three estates. NEA stated that mosquitoes will not be released directly into homes.

The three estates represent a cross-section of typical housing estates in Singapore, and provide a good baseline from which to make comparative studies.

The findings will support the design of another field suppression trial to be held over one to two years in 2017, to test if the technology is effective in bringing down mosquito populations – and by extension, possibly impacting the spread of dengue. If the tests are successful, NEA could roll-out this method to fight dengue in high-risk areas from 2019.


Similar small-scale releases of Wolbachia-carrying mosquitoes were carried out in other jurisdictions such as the Unites States and Thailand, with tests in China and French Polynesia having met with some success. A 2015 study in Guangzhou reported an over 90 per cent reduction in the Aedes mosquito population.

The trial was previously announced by Environment and Water Resources Minister Masagos Zulkifli in April 2016, during the Committee of Supply debates. It also comes after the NEA previously warned that Singapore could see a record 30,000 dengue cases in 2016. Despite efforts to eradicate mosquito breeding habitats, the NEA said Singapore remains vulnerable due to its location in a dengue endemic region, and low herd immunity in the community.


Speaking at a community event on Saturday to raise awareness of the study, Mr Masagos said it was important to engage the public on the move, adding that “a new line of defence” was needed in the fight against dengue. But he also hopes the community can play its part. For instance, residents can volunteer to use fan traps from NEA to capture mosquitoes in their homes, and all should keep up efforts to remove possible mosquito breeding habitats. Should mosquitoes continue to breed, Mr Masagos said, it would negate the effect of introducing the Wolbachia-carrying male mosquitoes.

“(The technology) does not replace the source eradication system. Therefore, whatever we’ve been doing all these years successfully – bring down the mosquito breeding places in our homes, in our construction (sites), in our public places, must continue,” said Mr Masagos.


Despite the international success of the use of Wolbachia in countries like China and Myanmar, one expert said the technology remains in its infancy. Infectious diseases expert at Mount Elizabeth Hospital, Dr Leong Hoe Nam said while he sees no major ill effects on human health, Wolbachia’s effectiveness could vary from environment to environment.

He said: “The biggest drawback is we don't really know what's going to happen. Many experiments have been done in the lab, trying to look at the different forms or possibilities - even looking into the different strains of Wolbachia, and how they will affect (mosquitoes). Going into a small trial in selected areas is the way forward."

Dr Leong said the lack of certain strains of dengue in Singapore could indicate that the mosquitoes spreading the disease could differ slightly from that of the region.

"Singapore has a very unique property in that only Dengue Strains 1 and 2 exist in Singapore - 3 and 4, we hardly see them. Now if you cross the Causeway, we'll see 3 and 4 in Malaysia. And similarly in the Philippines, Indonesia and Thailand. This tells you that there is something unusual about Singapore, where we're extremely effective in getting rid of 3 and 4," he said.

"If the mosquito is slightly different, then would the use of Wolbachia make a change? Would we have the same result? We don't know. The only way to take it forward is with field testing, field experiments and gathering data. This data will not only help Singapore, but help the region and the whole world”.

- CNA/mo

NEA to release Wolbachia-carrying males in mosquito control trial
SIAU MING EN Today Online 27 Aug 16;

SINGAPORE – From October, male Aedes aegypti mosquitoes carrying the naturally-occurring Wolbachia bacteria will be released in three housing estates over the next six months, as part of a field study to determine their behaviour, with the objective of controlling the mosquito population.

One to three mosquitoes per person will be released regularly at public spaces – such as stairwells and void decks – around the blocks and houses in Nee Soon East, Tampines West and Braddell Heights.

This works out to about 1,500 male mosquitoes for 500 people living in 1 block of flats.

As male mosquitoes do not bite, they will not transmit any diseases. The National Environment Agency (NEA) has assured that these Wolbachia-carrying mosquitoes are safe and pose an insignificant risk to the ecology and no risk to human health.

The housing blocks in Yishun Street 21(Nee Soon East), Tampines Avenue 4, as well as landed homes in Jalan Riang and Jalan Sukachita (Bradell Heights), have been chosen because they are representative of the typical housing mix in Singapore.

The three areas also have had previous dengue outbreaks, and the NEA has been monitoring the mosquito population in these locations for up to three years to provide a baseline for comparative studies.

The Yishun Street 21 area will be used to study the mosquitoes’ lifespan, and how far and how high they can travel. The other two areas will be to determine how the male Wolbachia-carrying mosquitoes mate with the wild female mosquitoes, and how competitive they are against the wild male mosquitoes.

Gravitraps and ovitraps, which trap female Aedes mosquitoes and their eggs respectively, will be set up at public spaces in the selected release sites and their surrounding areas to determine the female Aedes population and the eggs’ hatch rates. Meanwhile fan-based mosquito traps will be placed in the homes of residents who volunteer to trap the male Wolbachia-carrying mosquitoes and monitor their flight range.

During a media briefing on Thursday (Aug 25), the NEA was asked why the study will be conducted after the traditional dengue peak season of June to October.

An NEA spokesperson said the timing would not affect the results, as they are not looking at how this particular field study would control dengue or suppress the mosquito population. A subsequent suppression trial could be conducted sometime next year.

The small-scale field study comes in the wake of a warning issued by the authorities in February that Singapore could face a historic high of 30,000 dengue cases this year, due to the El Nino phenomenon and the change in the type of dengue virus circulating among the population.

The previous record was 22,170 dengue cases in 2013.

Speaking to the media after the briefing, NEA director-general for Environmental Public Health Derek Ho said: “(Male mosquitoes) do not pose any additional pressure in the public sphere. People should not be experiencing more mosquito bites as a result of this study.”

There are two types of Aedes mosquitoes in Singapore: Aedes aegypti and Aedes albopictus. The former species thrives in the urban environment and is a more efficient vector for diseases such as dengue, chikungunya and the Zika virus. Native to Singapore, the latter prefers the greenery but are not as efficient as a vector for dengue.

Wolbachia is a naturally-occurring bacteria found in over 60 per cent of insect species, but not in the dengue-carrying Aedes aegypti mosquito.

The NEA’s Environmental Health Institute managed to rear local Aedes aegypti mosquitoes carrying the Wolbachia in their laboratories, and will be releasing only the male Wolbachia-carrying mosquitoes to mate with female Aedes mosquitoes. Eggs produced from their mating will not hatch because they are biologically incompatible.

Over time, this will reduce the Aedes aegypti mosquito population and the potential spread of diseases such as dengue.

While Singapore is looking at using the Wolbachia technology to suppress the Aedes mosquito population, there are also other countries using the same technology but to replace the Aedes population to block the transmission of diseases.

The latter approach involves releasing both male and female Wolbachia-carrying Aedes aegypti mosquitoes. As Wolbachia is passed on from the female Wolbachia-carrying Aedes aegypti mosquitpes to their offspring, this method is used to rear subsequent generations of Wolbachia-carrying Aedes aegypti.

The Wolbachia bacteria would protect the mosquitoes from viral infection and reduce the risk of dengue transmission. This is being tested in countries such as Australia, Vietnam and Indonesia even though its impact on dengue has not been proven yet.

An NEA spokesperson said Singapore went with the former approach as it was consistent with what the agency has been doing – to promote source reduction of mosquito population by removing breeding sites for instance.

Releasing both male and female Wolbachia-carrying Aedes aegypti mosquitoes might not be an acceptable approach to the public here, since more people may may get bitten by the female mosquitoes, the spokesperson added.

Other countries adopting this approach to control the mosquito population includes the United States, Thailand and Guangzhou, China. In the latter’s field study, it managed to suppress more than 90 per cent of its Aedes albopictus population.

The field study comes after the authorities spent the last four years carrying out various risk assessment and laboratory research studies to ensure that the Wolbachia technology is safe. During this time, they also consulted stakeholders such as academic experts, medical and healthcare professions and non-governmental organisations.

A Dengue Expert Advisory Panel was also appointed by NEA in June 2014 to continue to review study results.

Speaking to reporters on Saturday (Aug 27) after announcing the small-scale field study sites to Tampines residents, Minister for the Environment and Water Resources Masagos Zulkifli said it was important to engage the public for the study.

The Government could have "just released it (the Wolbachia-carrying Aedes aegypti mosquitoes) quietly" and shared the results thereafter, he said. But it is important for the public to know what the small-scale field study is about such as the methods behind it.

"For this stage, we are calibrating, we are not actually releasing (them) in millions or billions," said Mr Masagos.

While the NEA and public having been working very hard over the years to bring down and suppress the mosquito population and spread of dengue, Mr Masagos noted that Singapore is situated in a region which is endemic with dengue.

He added that as climate change will also affect Singapore's weather pattern,there is a need to have a "new line of defence" to deal with the situation. In this case, it is the release of the Wolbachia-carrying Aedes aegypti mosquitoes, said Mr Masagos.

Mdm Winnie Lim who has been living in Tampines Ave 4 for the past 15 years said the method used is good in the long-term. The 49-year-old housewife noted that fumigation may not completely eradicate the mosquitoes, but with this method, it would prevent the eggs from hatching. Additional reporting by Amanda Lee

NEA to test novel way of cutting mosquito numbers
Amelia Teng, Straits Times AsiaOne 28 Aug 16;

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

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."

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