Magazine article Science News

The Malaria Parasite: Change and Conquer

Magazine article Science News

The Malaria Parasite: Change and Conquer

Article excerpt

A parasitic relationship resembles a biological arms race. Over evolutionary time, an infected host puts up a new defense to stave off a parasite, only to have that parasite evade the defense and sharpen its skills for circumventing the host's next defensive strategy. And so on, and so on, in a biochemical escalation process that usually ends with the parasite attaining the upper hand.

This change-and-conquer strategy has made it particularly difficult for scientists to develop vaccines against parasites, including the most dangerous malaria organism, Plasmodium falciparum (SN: 5/4/91, p.276). Now, researchers led by David J. Roberts of John Radcliffe Hospital in Headington, England, have figured out part of the protein shell game that keeps the malaria parasite in business. A better understanding of this process could lead to new approaches for treating and preventing the deadly disease.

Once the malaria parasite infects a host's red blood cells, it makes proteins that help the infected cells stick to the inner walls of blood vessels. In the June 25 NATURE, Roberts' group reports that P. falciparum can mutate these proteins at a rate of 2 percent each generation. This rapid mutation rate helps the organism evade the immune system and avoid traveling to the spleen, where a red blood cell carrying it could be destroyed, the researchers conclude.

P. falciparum has a complex life cycle. Infected mosquitoes inject the parasite's first stage, the sporozoite, into a host while drawings a blood meal. Sporozoites find their way to the host's liver, where each can divide into thousands of merozoites. After roughly a week, an army of merozoites leaves the liver to take up residence in the host's red blood cells. Later, the red cells explode, some releasing more merozoites and others releasing gametocytes, the parasite's sex cells. This causes the fever and chills characteristic of malaria. …

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