Suppressing mosquitoes - the only way of controlling dengue

There is no vaccine against dengue, an emerging tropical disease regularly also hitting tourists, so the only way of controlling it is by suppressing the mosquitoes transmitting the disease. Easier said than done, and cooperation of the local communities is an important factor in the success of a campaign. So observed scientists from the Antwerp Institute of Tropical Medicine (ITG). For her work in dengue control on two continents ITG-researcher Veerle Vanlerberghe obtained a PhD at the ITG and Ghent University.

Since the sixties the yearly number of new cases of dengue - also known as breakbone fever - has grown thirtyfold. Forty per cent of the world population is at risk of infection by the dengue virus. Every year fifty million people become infected. Light cases are similar to influenza, including heavy fever, headache, excruciating muscle pains. In severe cases the number of platelets in the blood crashes, which leads to a half million cases of bleeding and 25 000 deaths per year. There is no vaccine, and no medicine. Luckily, most people recover spontaneously. In severe case, physicians can support the recovery with symptomatic measures, like administering fluids or a blood transfusion, but only if they react fast enough and follow up the patient and his fluid balance closely.

The only meaningful action is controlling the mosquitoes that transmit the virus - mostly Aedes aegypti. Several control strategies have proven effective - in controlled circumstances. In everyday reality they leave much to be desired, as Vanlerberghe showed. For instance because the cultural differences between people were not taken into account: do they accept your approach, do they change their behaviour, do they change it permanently? Do they use the insecticide curtains they received against the mosquitoes, or for fishing? Do they accept fishes that eat mosquito larvae in tanks for household water?

In Cuba Vanlerberghe observed that management of water reservoirs and other mosquito breeding places works better when the local community is involved. People are prepared to go the extra mile and supplement the government programme, and they continue to do so when the research programme has ended. Vanlerberghe was the first to examine the long-term effects of involving the local communities. This involvement not only is more effective, it also is cheaper.

In Venezuela and Thailand she observed how important cultural factors can be: an overwhelming majority of people accepted the use of long-lasting insecticide treated curtains, but only one in five was willing to use insecticide treated jar covers.

Another observation was: don't take cooperation for granted. The insecticide treated curtains might be long-living, their use wasn't. People gradually stopped using them. To make them really effective, supporting promotional campaigns are needed, and they too cost money.

Thus, Vanlerberghe concludes, if you want to control mosquitoes, laboratory tests won't do the job. You will have to take into account human behaviour, epidemiological information and the exact behaviour of the mosquitoes.