NEA to explore biological control methods to tackle dengue

Channel NewsAsia 15 Jun 14;

SINGAPORE: The National Environment Agency (NEA) is exploring the use of biological control methods to control the spread of dengue in Singapore.

One of the techniques involves the use of Aedes aegypti mosquitoes, which are infected with a certain bacteria, to control their population.

In this method, male Aedes aegypti mosquitoes are infected with wolbachia, which are a type of naturally occurring bacteria found in more than 60 per cent of insect species, such as butterflies and fruit flies. However, the Aedes aegypti mosquito does not carry this bacteria.

When a male mosquito infected with this bacteria mates with a female mosquito, they produce sterile eggs that do not hatch. This will then lead to a fall in the Aedes mosquito population, and help to curb the spread of dengue.

The use of such methods is being studied in countries such as Australia, Vietnam and Indonesia. NEA said it is monitoring the results of these overseas trials.

The NEA's Environment Health Institute has been carrying out laboratory research studies on this technology.

It is part of a larger programme aimed at curbing dengue transmission.

NEA has appointed a panel of local and international experts to provide advice on new ways of dengue control, and their safety concerns.

The panel is chaired by epidemiologist and entomologist Professor Duane Gubler, who is the founding director of the Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, Singapore.

Panel members include entomologist Professor Stephen Higgs, research director of the Biosecurity Research Institute and associate vice president for research at Kansas State University; and epidemiologist Associate Professor Vernon Lee from the Saw Swee Hock School of Public Health, National University of Singapore. Professor Lee is also the head of the Singapore Armed Forces' Biodefence Centre.

This is in light of the dengue challenge Singapore faces, especially during the hotter months from June to October, traditionally the peak season for dengue transmission.

During this period, the Aedes mosquitoes breed faster. The incubation period for the dengue virus they carry, is also shorter.

The number of dengue cases has been on the rise, from 292 cases in the week of May 11-17, to 461 cases in the week of June 1-7.

- CNA/ac

Babyless future for dengue mozzies?
Carolyn Khew My Paper AsiaOne 16 Jun 14;

SINGAPORE - Mess with us, and we may even make you sterile. This seems to be Singapore's message to the dengue-spreading mosquito as the Republic considers using biological weaponry to tame the problem.

Since last year, the Environmental Health Institute (EHI) has been carrying out laboratory studies on using Wolbachia, a naturally occurring bacteria, to help suppress the breeding of Aedes aegypti mosquitoes.

This method of biological control involves using Wolbachia-carrying male Aedes aegypti mosquitoes to mate with Aedes aegypti females to produce eggs which do not hatch.

So far, lab results seem positive and the National Environment Agency (NEA) has appointed a panel to assess the possibility of taking this a step further.

Speaking to reporters at the launch of the "Do The Mozzie Wipeout" campaign 2014 yesterday, Grace Fu, Second Minister for the Environment and Water Resources, said that Singapore was "not under any pressure" to use this method of dengue control.

"Of course, we want to fight dengue as quickly as we can, but we also want to make sure that the study is thorough and safe," she added.

EHI's studies showed that male Aedes aegypti mosquitoes here which carry the bacteria are "sterile" when they mate with female mosquitoes in the field. They are also able to compete with other males in the wild for mates.

A newly formed panel, made up of six local and foreign experts, will assess the suitability of using this method for dengue control.

The panel will convene in August. It includes experts such as Duane Gubler from the Duke-NUS Graduate Medical School and the head of the Singapore Armed Forces' Biodefence Centre, Vernon Lee.

Another panellist, Timothy Barkham, told My Paper in an e-mail interview that it was still "premature to make strong comments" about the method at this time but it "makes sense to consider all options".

"Working harder at vector control has not solved the problem, so it makes sense to consider all options, including the Wolbachia technology, which uses laboratory-bred mosquitoes to deliver the Wolbachia to wild mosquitoes," said the associate professor at the department of microbiology, National University of Singapore.

"Mosquitoes are much better at finding other mosquitoes than we are. So it sounds attractive to use them in this way."

In April, British scientist Steven Sinkins told My Paper that the bacteria do not affect humans.

"It originates from fruit flies, so even if humans are eating any fruit they are probably eating little bits of Wolbachia from the fruit flies. It doesn't do any harm," he said.

Last year, British company Oxitec successfully conducted a trial in Brazil where male mosquitoes that were genetically modified were released to produce offspring which died before reaching maturity. The mosquito population was brought down by 96 per cent over six months.

Last year saw the highest number of dengue cases on record here, with more than 22,000 cases. As of June 7 this year, about 7,000 cases have been reported.

NEA looking to infect Aedes mosquitoes in dengue fight
Today Online 16 Jun 14;

SINGAPORE — For the first time, the National Environment Agency (NEA) is considering the use of biological control methods to limit the spread of dengue, by infecting male Aedes mosquitoes with a type of bacteria that results in females producing eggs that do not hatch.

The NEA’s Environmental Health Institute (EHI) has tested the use of the Wolbachia bacteria in the laboratory, but not in the field. A panel of experts has been set up and will convene in August to look into whether the use of the technology — which has been around since the ’60s and is being tested in Vietnam, Indonesia and Australia — is safe.

There was a record 22,170 dengue cases last year. About 7,000 cases have been reported this year, with the traditional peak period — June to October — only beginning.

Announcing the NEA’s plans at the launch of the Do The Mozzie Wipeout campaign yesterday, Second Minister for the Environment and Water Resources, Ms Grace Fu, said the Government had found the Wolbachia method to be interesting and probably applicable. “We are not under any pressure, of course. We want to fight dengue as quickly as we can, but we also want to make sure the study is thorough and safe,” she added.

Wolbachia technology involves infecting Aedes mosquitoes with Wolbachia — a naturally-occurring bacterium found in more than 60 per cent of insect species. When a male Aedes mosquito carrying Wolbachia mates with a female, the eggs produced do not hatch. The aim is to reduce the Aedes population to a level where dengue transmission cannot be sustained.

While the number of dengue cases so far this year is about 25 per cent below that of the same period last year, Ms Fu said this was still too high.

The Dengue Expert Advisory Panel consists of local and foreign experts and is led by epidemiologist and entomologist Professor Duane Gubler, founding director of the Emerging Infectious Diseases Programme at Duke-NUS Graduate Medical School.

Commenting on the Wolbachia method, Prof Gubler said in an email: “The main advantage of this and the other new methods in the pipeline is that they will control the mosquitoes that are breeding in hidden larval habitats that cannot be controlled by current methods.”

Lab studies by the EHI have shown that mosquitoes carrying Wolbachia have lower transmission potential for all dengue serotypes, as well as for the chikungunya virus. Preliminary data has also shown that male Aedes mosquitoes carrying Wolbachia can compete with wild males for female attention.

However, Monash University Dean of Science Scott O’ Neill said although the technology was powerful, releasing only male mosquitoes with the bacteria is not the most effective. Releasing both males and females infected with the bacteria would greatly reduce the ability of resident mosquitoes to transmit dengue between people, he said. He also noted that the approach Singapore was considering could be costly, as it will require continual releases of male mosquitoes to control the wild mosquito population.

Prof Gubler said other new technologies for tackling dengue could become available in the next three to five years. “These include new insecticides, genetically-modified mosquitoes (sterile male release), vaccines, antiviral drugs and therapeutic antibodies. None will likely be totally effective when used in isolation, but all show great promise if used in an integrated and synergistic programme,” he said.

Meanwhile, Ms Fu said the NEA had conducted more than 1.5 million inspections this year and would continue to focus on areas that have higher potential for dengue transmission. As of June 9, the NEA has issued 373 notices to attend court and 34 stop-work orders. There were 16 court prosecutions involving eight contractors.