Expert questions dengue eradication strategy

 The tragic dengue deaths including that of an eight year old girl earlier this year bring home to us that in T&T dengue is endemic, a permanent state of affairs in T&T, and occasionally we suffer from outbreaks which means a surge in cases of dengue. The Ministry of Health has advised that it is possible to reduce the conditions favourable for the breeding of the insect vector by cleaning up our environment, clearing weeds, emptying uncovered water tanks, cans, bottles, jars and vessels holding water, cleaning watercourses, and ensuring domestic hygiene. Our guest columnist in this two-part series is world expert on dengue, Professor Dave D. Chadee from the Department of Life Sciences, University of the West Indies who questions the dengue control strategies used in T&T.
One of the missions of the University of the West Indies is to conduct basic and applied research which serves to “explore solutions to priority national and regional problems and challenges; create significant new knowledge; elucidate important contemporary social issues; and provide a sound basis for public policy formulation and decision making”. This responsibility to conduct studies or research relevant to the needs of the Caribbean people is aptly demonstrated in the work being done on dengue fever: on the virus; the epidemiology of the disease and transmission dynamics as well as on the vector Aedes aegypti (population genetics, ecology, behaviour, insecticide resistance and control).  Over the last seven years over 60 research studies have been conducted and published in international peer reviewed journals and most studies have been presented at local, regional, and international scientific meetings. Today the research findings from this UWI programme are being used in dengue and vector control programmes in Cairns, Australia, South East Asia, Peru and in Puerto Rico but not in Trinidad–a serious gap remains in translating knowledge into practice.

In Tobago as early as 2003 a switch in major mosquito breeding sites from water drums to small containers was reported because of the replacement of water drums by tranks, especially in the Central district. Why, for example, did Trinidad not adopt the strategy of replacing water storage drums with closed tanks? A more dramatic effect may have been expected in Trinidad where drums account for 70 per cent of mosquito breeding sites while, prior to replacement, only 35 per cent in Tobago. The Ministry of Health figures show over 1800 reported dengue cases in July 2011 and the current dengue programmes are being run by three different ministries–Local Government is conducting a source reduction programme or clean-up campaign but unfortunately this will remove less than 5 per cent of the mosquito breeding sites. This strategy was advocated in the 1980s by the Pan American Health Organization and was evaluated in 4 different geographical areas but they all failed to reduce the vector populations to below disease transmission levels. The education programme being run by the Ministry of External Affairs and Communication is targeting householders and is excellent but will have long term benefits rather than short term relief to householders.

This is one of the major drawbacks of health education messages—the population must read, understand the message, plan (intend to change their behaviour), implement the behaviour change, and maintain their enthusiasm for cleaning and maintaining a mosquito free environment. The Insect Vector Control Division is currently carrying out their normal Aedes aegypti control programme which is reactive to reports of dengue cases rather than proactive. This reactive approach cannot be criticized in the short term but its impact and value may be less than optimal. There is an urgent need to develop proactive approaches which involve early warning systems and better strategic planning. After 35 years of the Aedes aegypti eradication and control programme (1976-2011) no progress appears to have been made, though research has shown that with the same materials and manpower more strategically deployed, significant reductions in mosquito populations are possible.

To be continued.

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