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  Straits Times Forum 27 Jun 07
Carry out outdoor fogging only in two instances
Reply by NEA

Straits Times Forum 20 Jun 07
Reduce frequency of outdoor fogging
Letter from Jennifer Cheng May San (Ms)

Today Online 14 Jun 07
A buzz that could spoil your holiday
Tan Hui Leng

Straits Times 14 Jun 07
NEA says halting Aedes breeding the way to go
Outdoor fogging not so effective against mosquitoes that thrive indoors
By Arti Mulchand

WITH two dengue deaths and no let-up in infections, questions are being asked about the battle plan by the National Environment Agency (NEA), particularly its choice of weapons.

But yesterday, the NEA and its scientists defended the stra- tegy of depriving mosquitoes of breeding places and fogging only when necessary. They insist it is the soundest strategy in dealing with the dengue- causing Aedes aegypti.

It is also the strategy recommended by the World Health Organisation.

'A solution needs to be suited to the country it is being used in, and you have to know the mosquito you are dealing with,' said Dr Christina Liew, a medical entomologist with the Environmental Health Institute.

Dr Liew, along with representatives from the Environmental Health Department and Singapore Pest Management Association (SPMA), was responding to alternative ways mooted to deal with dengue.

One idea came from pest management expert Carl Baptista, from Origin Exterminators - to treat indoor and outdoor surfaces with pesticides that would have a residual effect, killing mosquitoes if they came to rest on them.

It would be easier than getting them while in flight, he said.

But Dr Liew refuted its effectiveness, explaining that residual spraying on walls and outdoor surfaces is recommended for malaria-causing Anopheles mosquitoes because they rested on walls.

The Aedes aegypti also tends to breed and rest indoors, but not on walls.

'Scientifically, it may make sense...but it is not practical, is inefficient and ignores the way the Aedes aegypti behaves in real life,' she said. It would also be time-consuming and labour-intensive to cover whole surfaces with insecticide, and could have environmental and human health consequences.

The indoor method is limited too, Dr Liew said, citing a 1970 Thai study indicating that 90 per cent of Aedes aegypti were found on surfaces like clothes and bed covers that cannot be sprayed with residual compounds.

It is not the first suggestion the NEA has shot down.

The proposal to use traps that attract and kill mosquitoes will not work because the mosquito population here is small, she said. Tested traps caught moths, flies and other mosquito species.

Constant outdoor fogging is no help either, said Mr Tai Ji Choong, head (operations) of the Environmental Health Department. Fogging means having to be 'at the right place, at the right time', said Mr Tai. It works best when the insecticide hits the adult mosquitoes in flight, a 2005 NEA study found.

And excessive fogging is a waste of money; it may have environmental consequences too. Mosquitoes may also develop resistance to the insecticides quicker.

The NEA constantly advises homeowners and pest control companies not to over-fog outdoors. Since 2005, the NEA has brought down outdoor fogging by 50 per cent, it says.

But what does not help, said Mr Ng Say Kiat, director of the SPMA's Institutional Agencies Group, is nervous clients demanding fogging. 'They want to see smoke and hear noise so they feel that something is being done about dengue.'

Ironically, the one time fogging needs to be done is when the NEA faces the most resistance - indoor fogging in areas when there are known dengue clusters. Close to 60 per cent of homeowners say no to it, said Mr Tai.

In the final analysis, Dr Liew said, it is 'all about using the right tool at the right time.' arti@sph.com.sg

Today Online 14 Jun 07
A buzz that could spoil your holiday
Tan Hui Leng huileng@mediacorp.com.sg

EVEN as thousands of Singaporeans head abroad this month, an ominous buzz threatens to ruin the holiday mood.

The Aedes mosquito is spreading its wings across South-east Asia, casting not just Singapore, but also Malaysia, Thailand and even traditionally unaffected places such as Hong Kong, in the shadow of a dengue scourge.

Although changes in the environment and the dengue strain remain the key reasons for the spike in dengue cases here, "there is some concern that there could be an increase in imported cases due to the holidays", said Dr Amy Khor, Senior Parliamentary Secretary of the Ministry of Environment and Water Resources.

In Malaysia, between 200 and 300 cases are reported weekly, putting it "on par with countries like Singapore", the country's parliamentary secretary to the Health Ministry, Mr Lee Kah Choon, said on Tuesday.

By May 26, a total of 20,658 people in Malaysia had contracted dengue this year, a surge of 55 per cent over the corresponding 2006 figure. Singapore has recorded 2,472 cases of dengue infection thus far this year, an 89 per cent jump over the same period last year.

"This has been the pattern for the country over the past month. It is probably due to the weather we have been facing – rain with intermittent dry spells," Mr Lee added.

While the Malaysian authorities have met with Singapore's National Environment Agency to share information and research results on the Aedes mosquito, both countries cannot escape from the changing climate worldwide.

In Indonesia, the Asian Development Bank developed a model suggesting that dengue might rise three-fold in the country due to climate change.

This year, more than 68,000 dengue cases were recorded, out of whom about 750 died. Figures look seemingly grim in Thailand, with the country reporting more than 11,000 cases of dengue and 14 deaths by this month, up 18 per cent from the same period of 2006.

Thai Researcher Anond Snidvongsna Ayutthaya of Chulalongkorn University believes that climate change is a possible reason for the outbreaks in new areas. "High temperatures in the dry season and the earlier arrival of the rainy season are good for mosquitoes to lay eggs and hatch," he told The Nation. "If it is proved that the spread of dengue fever is due to the impact of global warming, we cannot fight it with traditional measures."

Even though dengue is endemic to South-east Asia, experts believe global warming is worsening the situation and could produce more virulent strains of the dengue virus.

Hong Kong expert in infectious diseases Dr Lo Wing-lok told Reuters that "mosquitoes are becoming more active year by year and their geographical reach is expanding both north and south of the Equator" due to global warming. Dengue could even become endemic to Hong Kong and southern China.

"Even Singapore, which is so affluent and modern, can't exercise adequate control," he added. And with the mid-year school holidays in full swing here, it also means that more may be vulnerable to contracting dengue outside of Singapore. From January to April, 12 per cent of dengue cases were imported, up from 9 per cent last year. But as of last week, it had gone down to 9.1 per cent again.

"You could get dengue any time but this is really the high-risk month," Dr Khor told Today.

She noted that as dengue is endemic in the region, the risk of contracting dengue overseas is not necessarily higher than in Singapore — especially since governments around the region are also putting in efforts to curb the dengue scourge.

But with more travelling out of Singapore, it also means that more may come back with imported dengue.

The Singapore Health Ministry advises travellers to guard against mosquito bites by taking precautions such as wearing long-sleeved clothes, using mosquito nets, coils or electric vapour mats, and applying insect repellent over the exposed parts of the body.

Straits Times Forum 20 Jun 07
Reduce frequency of outdoor fogging
Letter from Jennifer Cheng May San (Ms)

I READ in The Straits Times that outdoor fogging kills less than 4 per cent of mosquitoes. There is thus hardly anything to be gained from fogging.

However, the disadvantages are many: It harms the environment. It harms human health. It builds up mosquitoes' resistance to increasingly more chemicals.

The compounds of private condominiums are fogged every week, exposing both the environment and humans to risk regularly.

Should such fogging be stopped altogether? Or should the frequency be at least reduced to monthly? Could the authorities issue some guidelines in view of the ineffectiveness of outdoor fogging?

Straits Times Forum 27 Jun 07
Carry out outdoor fogging only in two instances
Reply by NEA

I REFER to the letter, 'Reduce frequency of outdoor fogging' (ST, June 20).

The National Environment Agency (NEA) would like to reiterate that the insecticide, pirimiphos-methyl, and the carrier solution, kerosene, used in thermal fogging by the NEA and its pest-control contractors are allowed under WHO guidelines.

The insecticide is diluted to a level safe for use, as recommended by the manufacturer. While this concentration is enough to kill mosquitoes, it is not hazardous to a human being.

At this concentration, the insecticide has a low toxicity to man and to non-target organisms, including mammals, birds, reptiles and fish. It degrades quickly in the environment and also does not harm plants.

The NEA is aware of the fogging practices in private condominiums and has been actively engaging the management committees and managing agents of these properties not to fog indiscriminately.

NEA's primary dengue-control strategy has been source reduction, that is, to reduce or remove all potential mosquito-breeding sites. Fogging should be carried out only when there are dengue-fever cases or when the adult Aedes-mosquito population is high so as to prevent more people from contracting dengue fever.

Besides sending circulars to condominium managing agents advising them to move away from the mentality of carrying out fogging as a routine to control mosquitoes, to focusing on preventing mosquito breeding, NEA holds regular dialogues with the pest-control industry to update its members on best practices in mosquito control.

In this regard, the Singapore Pest Management Association is working in partnership with NEA to advise pest-management companies against unnecessary fogging.

We have also been closely monitoring fogging operations carried out by the industry and note that there has been a 50 per cent reduction in fogging activities since November 2005.

Pest-control operators in Singapore are licensed by NEA and trained to carry out thermal fogging in accordance with established practices. To ensure the safe use of the insecticide, all licensed pest-control contractors must adhere closely to the manufacturer's recommended dosage and the specified safety and precautionary measures.

We thank Ms Jennifer Cheng for the feedback and appreciate her concerns.

S. Satish Appoo
Director Environmental Health Department
National Environment Agency
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