Killing malaria.

As early as the 16th century, B.C., Egyptian papyruses described symptoms like those of malaria, a disease researchers have been trying unsuccessfully to eliminate, or at least control, for hundreds of years. But for generation after generation, the parasite and the mosquito that carries it have proved resistant to drugs and pesticides.

Malaria is now the world's most prevalent disease, and one of the deadliest. At present, some 250 to 300 million people are infected with malaria parasites, and of the 110 million who develop the disease every year, about 2 million die. Half of those who die are children, often under the age of 5.

But despite this discouraging history, researchers are beginning to report progress. More than 20 years ago, Chinese scientists confirmed the antimalarial qualities of artemisinin, known in Chinese as qinghaosu (pronounced ching-how-soo). Artemisinin, a substance extracted from a fern-like plant called Artermisia annua, has been used in China as an anti-malarial drug for more than 1,500 years. Now, scientists have developed derivatives of artemisinin that can be administered either orally or by injection. Both forms of the drug are now used widely in Southeast Asia and in parts of Africa and Latin American. Injectable artemisinin has been found to act more rapidly than all other antimalarials and to be effective against multi-drug-resistant parasites. Although it is not yet approved for distribution in any developed country, the World Health Organization and some pharmaceutical companies are studying the drug's safety and effectiveness.

In another potential breakthrough, Manuel Patarroyo, a biochemist at the Immunology Institute of the National University in Bogota, Colombia, has developed what appears to be the first vaccine effective at warding off a parasitic disease. Known by its chemical name, SPf66, Patarroyo's malaria vaccine has been shown to protect between 40 and 66 percent of participants in field trials from the most common and deadly strain, Plasmodium falciparum, which is responsible for 95 percent of malaria cases.

Although Patarroyo's initial field trials were criticized by North American and European scientists because they did not meet international protocols, he answered their skepticism by conducting trials that did meet those standards. One of those trials, completed in 1992 in Ecuador, showed that the vaccine was successful in protecting 66 percent of the volunteers from the common malaria strain. All in all, the vaccine has been tested on 41,000 people in Brazil, Colombia, Venezuela, and Ecuador over a span of five years. There is now enough serious interest in SPf66 at the international level that the World Health Organization is working with the Walter Reed (U.S.) Army Institute of Research to test the vaccine in parts of Africa and Asia.

Meanwhile, other researchers are approaching the disease from a completely different perspective: studying the feasibility of altering the mosquito's genetic makeup so that it will be unable to carry and transmit the parasite to humans.