The strategies used in the prevention and control of dengue are contained in the Vector-borne Diseases Control Programme Sixth Malaysia Plan (1991-1995). These strategies are directed both at the larval and adult stages of the Aedes mosquitoes. For larval control, the activities carried out are source reduction measures, use of Abate larvicide, regular house inspection and enforcement of the Destruction of Disease-bearing Insects Act (DDBIA, 1975). Control measures include fogging activities when a case is notified and conducting case investigations and contact tracing. Health education activities are carried out routinely as an integrated approach for the prevention and control of dengue. The objectives of the control programme are : 1. to reduce the breeding of Aedes mosquitoes to a level below 2.5% Aedes House Index and below a Breteau Index of below 10% 2. to promote public support and community participation in the prevention and control of dengue 3. to get the full participation of the local authorities in dengue control activities. The overall control programme is very ambitious with the following targets in mind under the Sixth Malaysia Plan (1991-1995) : 1. to reduce the incidence rate to less than 6 cases per 100,000 population 2. to reduce the case fatality rate to less than 0.4%. Vector control against the Aedes adult and larval mosquitoes is given emphasis and the following activities are promoted.
(a) Source reduction The objective of this exercise is the elimination of Aedes mosquito breeding grounds in and around the home environment, state lands, public parks, construction sites, factories, government premises, schools and cemeteries. This is carried out with community involvement together with various other agencies as well as the local health authority. One of the problems encountered in source reduction is illegal dumping of household refuse by the roadside. This creates favourable breeding sites for the Aedes mosquitoes. To overcome this problem, the local health authority has stepped up scavenging services and provided additional bins at designated areas. Surveys carried out recently have identified neglected and unusual breeding sites which hamper source reduction efforts. Some of these breeding sites are cocoa pods, septic tanks, abandoned housing projects, roof gutters, refrigerator trays and Chinese cemeteries.
(b) Use of Abate Larvicide The use of a suitable larvicide such as Abate is given emphasis in the dengue control programsedrgbhbik o
me. It is safe, effective and convenient to use, especially in water holding 305 containers. The householders are encouraged to put Abate sand granules into water storage containers so that Aedes larvae will not breed. Its effectiveness will last for about 3 months. Abate is easily available in many outlets in Malaysia and priced so that it is within the means of all. Bacillus thuringiensis H-14 was found to be effective in suppressing Aedes albopictus breeding in outdoor artificial containers (Lee and Cheong, 1987) and the use of spraying machines to disperse this agent is under investigation.
(c) House inspection for Aedes Breeding House inspection for Aedes breeding is carried out daily by the health authority. The purpose of house inspection is to impart health education to the people on ways and meansto prevent Aedes breeding including the use of Abate larvicide and to look for Aedes breeding in individual household. Another purpose of the house visit is to ensure that the people carry out source reduction measures. The results of the Aedes larval surveys can be used to assess regularly the Aedes situation and density and to pin-point high risk areas as priority areas for prevention. House inspection to assess risk of dengue outbreak is based on Aedes surveillance and the larval density is expressed as House Index and Breteau Index. Although these indices were useful indicators in the past (Cheong, 1986), recent studies have indicated that dengue continues to occur despite very low larval populations. A more sensitive surveillance method is sequential sampling using ovitrap (Jakob and Bevier, 1969). Lee (1991) used a similar technique and reported that an ovitrap larval index of 10% was crucial for the initiation of vector control to suppress a possible outbreak. The major setback to the wider use of ovitrap is that it is labour-intensive. For the past five years, an average of 3.5 million houses were inspected for Aedes breeding. Out of this total, 12,111 (0.34%) houses were positive for Aedes aegypti and 29,768 (0.84%) houses were positive for Aedes albopictus. One of the problems encountered in house inspection is the coverage and frequency of visits to houses not being up to expectation due to shortage of manpower. For effective surveillance and control, each house should be visited at least once a month but this is seldom, if ever, achieved.
(d) Enforcement of the DDBIA, 1975 The enforcement of the DDBIA, 1975, against anyone found having Aedes larvae breeding in and around his house is an effective but unpopular strategy. However, it must be emphasized that the basis of enforcing this Act is not entirely to elicit public acceptance of legislation but to highlight the role of the public in supportive activities and the importance of their participation especially in source reduction measures. Towards this end, the implementation of legislation will be supported by health education and viewed as a constant reminder and driving force behind the Ministry's 306 objective of seeking spontaneous and full community participation in the prevention of Aedes breeding.
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