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October 20, 2008
New insight found into genome of neglected malaria parasite

By Quinn Eastman

As international health authorities step up efforts to fight malaria, leading scientists say the stealthy Plasmodium vivax parasite deserves more attention. The complete sequ-ence of the P. vivax genome, reported in the Oct. 9 issue of Nature, could help scientists unlock its secrets.

Vaccine researcher Mary Galinski and her colleagues at Yerkes National Primate Research Center played a critical role in assembling P. vivax’s genetic information because the parasite cannot be cultured in the laboratory and can only be grown in living monkeys.

P. vivax is responsible for at least 25 percent of the roughly 500 million cases of malaria worldwide and is the major cause of malaria outside Africa.

Both P. vivax and P. falciparum, the dominant malaria parasite whose genomic sequence was published in 2002, are carried by mosquitoes and can cause fever, chills, headache, nausea and vomiting. What makes P. vivax distinctive is the “hypnozoite” phase of its life cycle, when the parasite lays dormant in liver cells for months or years after initial infection.

While P. vivax infection is usually non-lethal and doctors once considered it “benign,” an increasing number of reports show the parasite can kill, Galinski said.

Compared with P. falciparum, P. vivax’s ability to come back from dormancy, its faster development in the mosquito, and the outdoor biting behavior of the mosquitoes it prefers may make P. vivax more resilient to common control methods such as insecticide-treated nets.

The complete genetic sequence of P. vivax has revealed unique genes that appear to be important for invading the host’s cells and in evading the host’s immune system, Galinski said.

Galinski and Yerkes colleague Alberto Moreno also recently published studies of a P. vivax vaccine candidate. In the August issue of Vaccine, they showed that the vaccine effectively stimulated monkeys’ immune systems to produce antibodies, which in laboratory tests could block proteins the parasites use to invade blood cells.

The full P. vivax sequence and its analysis were a collaboration involving scientists from a dozen institutions and coordinated by the Institute of Genomic Research. The first author is microbiologist Jane Carlton at New York University School of Medicine.