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Drug resistance

While preventing malaria is relatively straightforward - DDT sprayed inside homes and insecticide-impregnated nets over beds - the treatment of it once infection has occurred is anything but. The use of cheap, readily available anti-malarial drugs throughout the tropics has resulted in widespread drug resistance. In the 1950s, chloroquine and sulphadoxine-pyrimethamine were so effective they were added to table salt in African countries to control malaria. Practically everyone in tropical regions had the chemical in their blood, and this led to drug-resistant mutations of the parasites. Today, chloroquine and its successors are ineffective in many areas. Drugs developed since then have proved either to have serious side effects or to be so expensive only tourists can afford them.

The most promising recent advance has come from China, where scientists have developed a plant-derived drug called artemisinin. When combined with mefloquine - developed in the US to protect soldiers during the Vietnam war - it has dramatically reduced malaria in south-east Asia, the most drug-resistant area of the world.

The use of this combination is now being taken up by the World Health Organization's Roll Back Malaria initiative, which will make it possible to treat an adult for less than $1. The next big challenge is to persuade aid agencies and international health organisations to distribute it. This will be difficult, given past experience showing the malaria parasite's ability to adapt and resist new compounds.

Other developments in the war on malaria include genetically engineering a new breed of mosquito that cannot carry the parasite and would eventually displace the Anopheles mosquito. Another is a bacteria derived from coconuts which, destroys mosquito larvae. But both these are expensive and a long way off. The anti-malaria world is more interested in an effective malaria vaccine. While advances have been made, there are major stumbling blocks. One is technical: the malaria parasite is able to escape the human immune defence mechanism by hiding inside cells, eluding antibodies.

Another is lack of international funding and co-ordination of research.

However, the EU recently funded a vaccine trial in the Gambia which resulted in temporary but high-level protection for adults. Its results have led to a larger trial involving children in Mozambique.

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