Malaria parasite older, more resistant than thought, study suggests

Wednesday, July 17th 2002, 12:00 am
By: News On 6

The tiny parasite that causes malaria may be older and more resistant to drugs than previously believed, according to a pair of new studies.

Researchers at the National Institutes of Health mapped large sections of the parasite's DNA to determine how far back it dates in evolutionary history and found it may have originated between 100,000 and 180,000 years ago _ instead of as recently as 3,000 to 5,000 years ago.

The difference is important when deciding the best way to fight malaria, a blood disease transmitted by mosquitoes that afflicts an estimated 500 million people each year and kills as many as 3 million.

If malaria DNA is fairly uniform genetically, implying it has more recent origins, doctors could more easily develop a vaccine or drugs to prevent or cure the disease. However, if the parasite's DNA has large variations, a vaccine that prevents one strain could lead to mutations that give rise to more resistant strains that could be deadlier.

The studies, led by Xin-zhuan Su of the National Institute of Allergy and Infectious Diseases at NIH, suggest the parasite is older and more genetically diverse.

``These parasites have accumulated a lot of mutations,'' Su said. ``And unfortunately, diversity does accelerate resistance.''

In another study also appearing in Thursday's journal Nature, researchers isolated a gene that allows the parasite to resist the effects of chloroquine, a common antimalarial drug.

The researchers found that the gene was not only more widespread than previously thought, but also that it had moved through the infected population from continent to continent with alarming speed, likely helping to shape the evolution of the parasite.

``It doesn't mean that any one place is getting any more resistant than others,'' said Dr. Joseph Vinetz, spokesman for the Infectious Diseases Society of America. ``But it's consistent with what we've already known, and that is this is a really smart bug.''

Scientists previously had believed that chloroquine resistance developed independently in only two areas of the world and slowly spread to other countries.

The studies suggests that drug treatment programs should be carefully monitored to limit the spread or increased resistance.

``I think that people in the field and in drug development are thinking mostly about multidrug therapy,'' said Dyann Wirth, a microbiologist who directs the Harvard Malaria Initiative.

In the first study, the NIH researchers compared the same 204 genes in the third chromosome of malaria parasites from five separate regions: Southeast Asia, Africa, South America, Central America and Papua New Guinea.

In the chloroquine resistance study, the researchers isolated 87 strains of parasite from malaria patients worldwide and compared 342 DNA markers to develop the first genetic ``fingerprint'' for the entire malaria genome.