Death By Mosquito

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DARLENE A. MURAWSKI / PETER ARNOLD

THE CULPRIT: The female mosquito needs blood to produce eggs. It transmits malaria parasites when it bites again

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To better understand why malaria has become such a threat and what can be done to stop the disease, it helps to know a little biology. Malaria is caused by four closely related parasites, the deadliest of which is Plasmodium falciparum, which has a particular fondness for anopheles mosquitoes. The parasites enter the bloodstream when an infected mosquito bites a human. Then they multiply inside the host's liver and red blood cells. (That's why pregnant women, who make lots of blood to nourish their growing fetus, are especially vulnerable.) Eventually the red blood cells burst with a new generation of parasites, causing fever, shivering, pain and sometimes death. The cycle of transmission is complete when another mosquito bites an infected person and picks up more parasites.

You might expect that one bout of malaria would lead to lifelong protection against the disease. But for complicated reasons, that is not the case. The illness tends to be less severe in adults who are continually exposed to the parasites. But when young children become infected, they are much more likely to suffer severe anemia and convulsions that may lead to permanent brain damage and death.

For decades, the best treatment for malaria was an inexpensive medication called chloroquine, first discovered in Germany in 1934 by a researcher working for Bayer. Chloroquine was so effective that it seemed it might vanquish malaria forever. But by the 1970s, the drug had been used so widely to treat all kinds of fevers, not just those caused by malaria, that the malaria parasites became resistant and doctors had to turn to a second medication, called sulfadoxine-pyrimethamine, or SP. But within five years, the parasites started to develop resistance to SP as well. Today resistance to both drugs is rampant in many parts of Africa, where resistant malaria parasites are the leading cause of death.

At the same time, efforts to control anopheles mosquitoes have been more or less abandoned. Part of the problem was the realization that malaria could never be completely eradicated from tropical regions the way it had been in the U.S. and other countries in temperate zones. There was also a growing backlash against DDT, a pesticide that is highly effective at attacking mosquitoes but whose indiscriminate use in agriculture killed many fish, beneficial insects and birds. Although only small amounts of DDT are needed to control malaria — usually in indoor-spraying campaigns — its toxic reputation made cash-strapped governments in Africa, which often must rely heavily on international donors, hesitant to use it.

So much for how things got so bad. The silver lining to all this heartache is that the outlines of a workable solution have at long last emerged. No one is promising an end to all deaths from malaria. But doctors estimate that hundreds of millions of people could be spared the illness and the mortality rate could be cut in half. The catch: although astonishingly inexpensive (at least by the industrial world's standards), an effective response is still beyond the financial resources of the poorest nations of the world, particularly those in Africa. There simply can be no progress without help from the developed world.

To be successful, any antimalaria campaign must do two things: treat the illness and prevent the transmission of parasites. Several pilot studies conducted in Africa have proved that combination therapy, in which at least one of the medications is derived from a plant called Artemisia annua, or sweet wormwood, easily destroys drug-resistant malarial parasites in the bloodstream. Using several drugs at once, often in the same pill, greatly decreases the risk that the parasites will become resistant. As an added bonus, artemisinin, the active ingredient in Artemisia annua, acts very quickly, further decreasing the chances of drug resistance.

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