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New approach to tackle dengue fever
Over 380,000 people have been protected from dengue fever in Vietnam thanks to a community approach to mosquito control. The strategy involves inoculating large water storages with crustaceans called Mesocyclops, which feed on mosquito larvae, preventing the growth of the most common dengue vector, the mosquito Aedes aegypti.
The investigators report that A. aegypti has been eradicated in most villages in the programme, and no cases of dengue fever have been reported in any of the villages since 2002.
A new strategy for dengue control
Brian Kay and Vu Sinh Nam describe a low-technology--but highly effective--strategy for control of disease-carrying mosquitoes in Vietnam. The main target of the strategy is the Aedes aegypti mosquito that transmits dengue fever.
Dengue is a classic emerging disease that illustrates the spectacular failure of top-down diseasecontrol methods and one of the negative impacts of globalisation on poor communities. The reasons for the emergence of dengue and dengue haemorrhagic fever are not fully understood, but widely recognised social factors include: deterioration of publichealth infrastructure, expansion of international travel and trade, and rapid increases in economically marginalised urban populations lacking basic services.
Densely populated shanty towns provide perfect conditions for the transmission of vector-borne disease. Mosquitoes need standing water to breed. Lack of reliable piped-water supplies mean that water must be stored in or near the home; inadequate disposal of non-biodegradable containers provide further breeding sites for mosquitoes. The types of container used by the mosquito to breed vary by location. An important element of the strategy described by Kay and Nam involves an assessment of which containers produce the most mosquito larvae, and therefore are the important ones to target. In Vietnam, with its predominantly rural population and saline ground-water near river deltas, large water-storage tanks are an important mosquito-breeding site.
The solution to this problem is a novel one, involving a form of biological control. Large water-tanks are inoculated with local species of Mesocyclops copepods, which live on various organisms, including mosquito larvae. However, other potential breeding sites, such as discarded containers, are too small to be treated successfully with Mesocyclops and need to be removed. Fortunately, the structure of Vietnamese society is well suited to community participation. The dengue-control programmes described by Kay and Nam are done
by communal health workers, paid healthcollaborators, and school teachers and pupils who inspect houses and collect discarded containers.
Kay and Nam report eradication of A. aegypti in most communes in the programme, and no subsequent cases of dengue in any of these communes. Compared with the rest of the country, the northern provinces are less suitable climatically for A. aegypti and for dengue transmission. Relatively few cases of dengue were reported in the northern provinces even before the programme began. Nam Dinh province is enlarged. 18 communes in this province where interventions were done are in black.
Use of Mesocyclops is most effective in medium to large water-containers, which are less frequent breeding sites in most cities. Initial study areas were specifically chosen for their suitability in this respect. Extrapolation of the strategy to western cultures seems even less certain, because community participation will be more difficult to establish and maintain in societies with a strong culture of individualism and dislike of visible organisms in the drinking water.
WHO's strategy for dengue control advocates "integrated mosquito control with community and intersectoral participation", but does not specify which methods are most appropriate. The Scientific Working Group on Insect Vectors and Human Health advocates genetic engineering to develop novel mosquitocontrol methods, and the improvement of existing biological insecticides. Even if scientifically achievable, these high-technology approaches to the control of dengue will only be a part solution, especially for low-resource areas that carry the largest disease burden.
Kay and Nam show that low-technology approaches to vector control can be effective if well planned and supported, with a strong emphasis on community participation. Their strategy is not a universal answer to the problem of dengue, but has the potential to make an important difference in rural communities.
On a global scale, most of the population increase expected during the next quarter century will occur in the urban areas of poor countries, whose population is projected to double from 2 billion in the year 2000 to about 4 billion in 2030. Providing basic services to this rapidly expanding urban population must be a top priority if further dramatic increases in dengue, as well as other infectious diseases, are to be prevented.
Source: The Lancet