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Number of cases falling since 2007, but disease still endemic to region
THE six- to seven-year cycle of dengue outbreaks has been broken, and chikungunya and malaria have also been brought under control, the National Environment Agency (NEA) announced yesterday.
 With dengue, the number of cases typically rises over a period of six years or so, and then climaxes in a major outbreak, explained Mr Tai Ji Choong, who heads operations at NEA’s environmental health department.
Since the last major outbreak in 2005, the number of dengue cases has gone into a long decline – from 8,826 cases in 2007 to 7,031 in 2008, to 4,497 last year.
If the dengue cycle was playing to form, these numbers should have been rising instead of falling, Mr Tai said.
In the first 33 weeks of this year – and with the May-to-October dengue breeding season almost done – the number of cases stood at 3,015, lower than last year’s total for the same period.
He attributed the year-on-year decline to the NEA’s disease management approach, which involves public environment and health agencies working closely with water agency PUB, the Housing Board and other public and private groups.
Called “integrated vector management”, the approach also involves reducing the use of fogging chemicals so the dengue-carrying Aedes mosquito does not become resistant to them, and designing buildings and bus stops so that possible mosquito-breeding spots such as gutters and bamboo-pole holders are not a part of their design, Mr Tai said.
He was speaking on the sidelines of the second Asia-Pacific Dengue Workshop, organised by the World Health Organisation (WHO), the NEA and the Ministry of Foreign Affairs.
The workshop, attended by 58 participants from 23 countries, aims to promote integrated vector management in the region and train participants in better field and clinical surveillance. It began yesterday and ends next Wednesday.
By WHO statistics, 2.5 billion people are at risk of dengue; the Asia-Pacific region alone sees between 200,000 and 500,000 cases every year and more than 2,000 deaths from the disease.
But many developing countries lack the manpower and funds to deal with the complex disease, for which no vaccines or anti-viral drugs exist.
NEA chief executive Andrew Tan said, also on the sidelines of the workshop, that despite Singapore’s disease control successes, it should not be complacent.
Dengue is endemic to the region, and changes to the environment here, such as the planting of trees and rooftop gardens, can inadvertently create new mosquito-breeding spots, for example.
Another challenge is that current methods of hunting down and destroying breeding spots are labour-intensive, he added.
To improve dengue control, the NEA is refining its risk-assessment maps and predictions, and studying ways to detect and kill mosquito larva more efficiently. It will also look at whether climate change shortens mosquitoes’ breeding cycles.
At the dengue workshop, France’s Pasteur Institute medical entomologist Paul Reiter suggested that releasing mosquitoes rendered genetically sterile could control the mosquito population and thus, dengue and other mosquito-borne diseases.
Mr Tan, when asked, said Singapore would be cautious about using such radical technology.
2 other diseases under control
w CHIKUNGUNYA
Singapore’s National Environment Agency (NEA) yesterday declared that the painful mosquito-borne disease chikungunya was not endemic here. But there had been cause for concern earlier because the viral illness, which first cropped up here through three imported cases in 2006, hit 718 people in 2008, partly as a result of a local outbreak.
Mosquito-control measures reduced the number to 341 last year, including 66 imported cases. This year, there have so far been seven local and 15 imported cases.
The NEA’s integrated vector management programme controls both dengue and chikungunya, as it targets the same two species of mosquito, Aedes aegypti and Aedes albopictus.
w MALARIA
A malaria task force is reviewing and upgrading drains following malaria outbreaks in Sungei Kadut and elsewhere last year, when 29 people fell ill. In all, there were 168 cases, of which 29 were local.
So far this year, malaria cases have returned to normal levels, with nine local and 109 imported cases.
The malaria task force involves many public agencies, including the Ministry of Defence, the National Parks Board, the Ministry of Health and the Singapore Land Authority.
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