Malaria Parasites Use "Cloaking Devices" to Trick Body

Amitabh Avasthi
for National Geographic News
October 8, 2008

Malaria parasites use elaborate forms of deception, such as molecular mimicry, to fool the human immune system, new gene studies say.

The discovery could lead to new vaccines for the disease, which kills millions and is rapidly becoming resistant to treatment.

Gene sequencing of two parasites, Plasmodium vivax and Plasmodium knowlesi, comes six years after researchers unraveled the genome of Plasmodium falciparum, the malaria parasite that causes the most fatal infections worldwide. Gene sequencing determines the order of chemical building blocks in a species's DNA.

While P. vivax is rarely fatal and causes less severe infections, it accounts for more than a third of about 500 million infections, most of them in Asia.

"The P. vivax parasite can lie dormant in the liver, and patients can get infected months, even years, after the first infection," said Jane Carlton, a parasitologist at the New York University Medical Center, whose team sequenced P. vivax.

"You cannot eradicate malaria unless you eradicate P. vivax," said Carlton, who co-authored one of a pair of related studies to be published tomorrow in the journal Nature.

A Stealthy Species

Malaria infections begin when parasites are injected into humans via mosquito bites. Once inside the body, the parasites enter the bloodstream and are quickly carried to the liver.

There, the parasites grow into a form that lets them infect red blood cells and proliferate. Subsequent mosquito bites ferry the parasites to others—and the infectious cycle continues.

Carlton and her team have discovered sets of genes and proteins that help the parasite successfully invade red blood cells and evade the immune system.

"Once the parasite is inside a red blood cell, it produces certain proteins to coat the surface of those cells," Carlton explained.

Continuous changes on the surfaces of the red blood cells prevent the body's defense mechanisms from detecting the parasites.

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