The malaria parasite is older and more diverse than previously thought, making it even harder to develop a vaccine against the lethal tropical illness. That's the conclusion of researchers at the U.S. National Institutes of Health after analyzing the genetic blueprint of the parasite.

The drug chloroquine used to be extremely effective in treating malaria. But in the late 1950's, resistance to chloroquine was beginning to show up in South America and Southeast Asia.

Experts assumed resistance to chloroquine that was spreading around the world came from those two regions. But new data published in the journal Nature by researchers at the National Institute of Allergy and Infectious Diseases reveals resistance was cropping up independently in geographic four locations. There were two areas in South America, one in Papua, New Guinea and one in Southeast Asia.

Investigators reached this conclusion after doing a complete genetic analysis of 87 parasites collected from all over the world, according to lead author Xin-Zhuan Su. He said, "This work, for one thing, demonstrates this parasite is very complex, diverse and also we found the drug resistance to chloroquine happened more frequently than we thought. So that argues that maybe we should have a closer monitor of the drug use and have some program when we introduce new drugs to treat them."

In a second paper, also published in Nature, Mr. Xin-Zhuan's team found through an analysis of more than 200 genes that the malaria parasite is at least 100,000 to 180,000 years old.

Previous, less extensive genetics studies put the parasite at between 3,000 and 5,000 years old.

Researchers were able to determine the parasite's age by the great number of differences in its genetic blueprint, genetic diversity that could only have occurred over a very long period of time.

Mr. Xin-Zhuan said this diversity makes malaria vaccine development that much more challenging. "Vaccine development in the field has been fifteen, twenty years. We do not have anything that looks good yet around. This is consistent with what we found, that the parasite is very complex and has the ability to change quickly, to respond to whatever you put to them."

That's bad news for the estimated 300 million people around the world who are infected each year with malaria, and the two million mostly children and infants who are killed by the disease.