Trial to curb Aedes mosquito numbers yields ‘valuable data’

ALFRED CHUA Today Online 8 Feb 17;

SINGAPORE — Some three months since male Wolbachia-carrying Aedes aegypti mosquitoes were released into three housing estates as part of a field study to control the mosquito population, results so far have been encouraging, with the National Environment Agency (NEA) saying the initiative has provided “valuable data”.

At one site — Tampines West — half of the mosquito eggs collected from there did not hatch — a promising step towards the goal of suppressing the mosquito population.

Eggs produced from a male Wolbachia-carrying Aedes aegypti mosquito and a female urban Aedes aegypti mosquito will not hatch, as they are biologically incompatible.

At a media interview on Wednesday (Feb 8), Professor Neil Ferguson, a member of the NEA’s Dengue Expert Advisory Panel, said the results so far show that the male Wolbachia-carrying mosquitoes are able to successfully mate with female urban Aedes aegypti mosquitoes.

“It indicates that the males will be able to compete effectively (against other urban male Aedes aegypti mosquitoes). That’s what we need in order to drive down the mosquito population,” Prof Ferguson said.

The six-month ongoing study, called Project Wolbachia-Singapore, also found out that male Wolbachia-carrying Aedes aegypti mosquitoes are able to live up to four days after being released in the urban environment, and can fly to high levels when released at ground level.

Prof Duane Gubler, who chairs the panel, said a male mosquito’s lifespan will affect its probability of mating with females. Noting that male mosquitoes typically live less than a week, Prof Gubler said if mosquitoes are released when older, they could be less potent. “If you reduce the age (at release) by a day, it could (yield significant results) over a large number of mosquitoes,” he added.

From October last year, male Wolbachia-carrying Aedes aegypti mosquitoes were released in Braddell Heights, Tampines West, and Nee Soon East, testing three study parameters: Fertility, mate-seeking behaviour, and flight ability.

The study will find out if these mosquitoes can help reduce the population of urban Aedes aegypti mosquitoes, which carry the virus that causes dengue fever, as well as the Zika and Chikungunya viruses.

The findings from this study will go into refining the design of a larger suppression trial slated to kick off later this year, said the NEA yesterday.

Despite the promising findings so far, the NEA has said they should not be relied on “as our sole strategy”.

“A strong, integrated vector-control programme with community participation, underpinned by Singapore’s well-established programme for the elimination of mosquito breeding habitats and the selective use of insecticides, where necessary, to control the adult mosquito population remain essential for dengue prevention in Singapore,” it said in a media release.

In January, the NEA warned that the number of dengue cases could increase over the next few months, reaching their peak by the middle of this year.

According to the NEA’s dengue website, the total number of dengue cases reported since the start of the year stands at 361, relatively low compared with the similar period in past years.

Last year, there were a total of 13,115 dengue cases, below the projection of more than 30,000 cases. Experts TODAY had spoken to previously had pointed to this decline as a result of the heightened awareness and control measures arising from the Zika outbreak last year.


Wolbachia-carrying mosquito study yields 'valuable' data: NEA
Vanessa Lim Channel NewsAsia 8 Feb 17;

SINGAPORE: Early findings from an ongoing six-month study showed that the viability of Aedes aegypti mosquito eggs collected from a site at Tampines West has been reduced by about half, said the National Environment Agency's (NEA) Dengue Expert Advisory Panel (DEAP) on Wednesday (Feb 8).

The small-scale field study involves releasing male Wolbachia-carrying Aedes aegypti mosquitoes to understand their behaviour and see if they can suppress the population of urban Aedes aegypti mosquitoes.

While the male mosquitoes may fly around and enter homes to seek out females and find shelter, they will not bite or transmit disease. Eggs produced from the male Wolbachia-carrying Aedes aegypti mosquito and a female urban Aedes aegypti mosquito will not hatch.

Since October 2016, these male Wolbachia-carrying Aedes aegypti mosquitoes have been released on a regular basis at three selected sites located at Braddell Heights, Nee Soon East and Tampines West.

These estates have seen dengue outbreaks previously and have Aedes aegypti mosquitoes present in the environment.

Professor Neil Ferguson, a DEAP member, explained the significance of the findings from the study: "This is important because it indicates that the male Wolbachia mosquito can successfully mate with Aedes aegypti female mosquito and that's what we need to drive down the mosquito population."

In addition, the study found that male Wolbachia-carrying Aedes aegypti mosquitoes are able to live up to four days after being released in the urban environment, and can fly up to high levels and travel more than 40m horizontally.

DEAP chairman Professor Duane Gubler, said: "This suggests that they are as fit as male wild Aedes aegypti mosquitos. It tells us how frequently you have to release these mosquitos, so that we can better calibrate their releases."

MORE WOLBACHIA-CARRYING MOSQUITOES MAY BE RELEASED

The study, called Project Wolbachia-Singapore, has made "good progress" and yielded "valuable data to guide the next phase of trials", said NEA in a media release on Wednesday.

It added that over the next few months, more data will be collected to refine the design of the larger suppression trial planned for later this year.

The suppression trial will test the utility and effectiveness of releasing male Wolbachia-carrying Aedes aegypti mosquitoes to surpress the Aedes aegypti mosquito population.

"Nothing the panel has seen has caused any hesitation in proceeding with the project. But there's a lot to be learnt before the decision to expand the project can be made,” said Prof Gubler.

To do that, experts have suggested tweaking the study to increase the number of male Wolbachia-carrying Aedes aegypti mosquitos being released.

"Right now, the preliminary data doesn't get us the results we want to see,” explained Prof Gubler. “We need to increase the number of mosquitos to be released to see a larger impact."

NEA appointed the DEAP in June 2014 to provide professional advice on new methods of dengue control, particularly on the use of Wolbachia-carrying male mosquitoes.

- CNA/xk

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