Serendipity The troops' tropical friend

NEXT WEEK I shall be heading off to India, which means that today I had to start taking my malaria tablets.

It is difficult to pin down the origin of malaria drugs, but a centuries- old legend tells of a boy lost in the jungles of the Bolivian Andes. Suffering from a burning malarial fever and at the point of death, he stumbled across a stagnant pool. When he drank from the pool, the water tasted bitter and he realised that it had been tainted by the bark of a neighbouring tree, known as the quina-quina. The bark was said to be poisonous, but the boy, anxious to quench his thirst, continued drinking. In the following days, the fever abated, the boy grew stronger, and he eventually found his way back to his village.

The bark, dubbed quinine, was brought to Europe in the 17th century, and its active ingredient isolated in 1820. By the 19th century, it had become a valuable commodity, a necessity for any nation that wanted to protect its troops while they conquered tropical countries.

The Dutch planted quina-quina seeds in Java, and by the mid-1800s they dominated quinine production. In order not to be reliant on those countries that controlled these plantations, other nations made various attempts to synthesise artificial quinine. In 1856, the British chemist William Perkin failed to make quinine, inventing aniline purple dye, otherwise known as mauve, instead. But that's another story.

During the First and Second World Wars, chemists came up with various alternatives to quinine, including chloroquine, which is what I am taking today. There is increasing concern, though, that the malaria parasite is becoming resistant to chloroquine and other commonly prescribed drugs.

A concerted effort is now being made to find new drugs, and one of the best candidates seems to be qing hao su, derived from the sweet wormwood plant of China.

Malaria is caused by a parasite, injected by mosquitoes into humans. The parasite lives in our red blood cells, where it digests the haemoglobin. Qing hao su kills the parasite by disrupting its digestive system. In China the drug has been used to treat malaria for more than 2,000 years - perhaps its effects were discovered during a serendipitous event similar to the one that revealed the effects of quinine.

Western doctors now use qing hao su to treat malaria, and they hope to employ it as a preventative drug. Rather than prescribing it on its own, however, they would try to combine it with another new drug, Malarone.

The theory is that a strain of malaria parasites which is resistant to qing hao su would be killed by Malarone and vice versa, making it inordinately harder for the parasites to become resistant to the combination of drugs.

Simon Singh is the author of `Fermat's Last Theorem' (Fourth Estate, pounds 6.99)