PARIS -- The malaria parasite has a broad and ancient genetic lineage, giving it the ability to sidestep potential approaches for a vaccine and become swiftly resistant to new drugs.

This is the gloomy news from two new studies that have sifted through the genetic code of plasmodium falciparum, the microscopic mosquito-borne parasite that kills millions of people each year.

A team led by Xin-Zhuan Su of the United States' National Institutes of Health built a family tree of the bug compiled from genetic mutations that have evolved among five different strains of the parasite around the world.

They conclude that P. falciparum came on the scene between 100,000 and 180,000 years ago.

That mirrors man's emergence from Africa -- an event that spread forestry and farming practices around the world and indirectly helped extend the range of the malarial mosquito, turning it into a powerful agent for disease.

The family tree shows wide genetic diversity, which is a major blow to hopes for drugs to kill the parasite, the study, published in Thursday's issue of the British journal **** Nature ****, says.

Under the Darwinian principle of Natural Selection, the genes that dominate in a species are those that enhance the creature's survival.

"If a vaccine controls only part of the P.

falciparum population, then it might alter the genetic composition of the surviving parasites," commented Andrew Clark of New York's Cornell University. "The frightening prospect is that such an imperfect vaccine might select for variants of P. falciparum that are more virulent, potentially undoing any progress towards mitigating this scourge."

In another study, also published in **** Nature ****, the Su team found that a gene that makes the parasite resistant to the common anti-malarial drug chloroquine is more widespread -- and has spread faster -- than previously thought.

Between 300 and 500 million cases of malaria occur each year, with the annual death toll estimated to range from at least one million to 2.7 million.

P. falciparum enters the victim's blood stream through the saliva of a malaria-infected mosquito as it sucks blood from the skin.

The parasites then burrow into the victim's liver, where they hole up and multiply. They then leave the liver and enter red blood cells.

Once inside, they multiply again, causing the blood cells to burst, releasing more of the parasites which go on to infect more blood cells, and so on.

Eventually, the parasites can destroy up to 70 percent of all red blood cells, causing severe anemia, fever, coma and death. Most of the victims are children under the age of five.