for National Geographic News
Malaria, a mosquito-borne illness, can be caused in humans by one of four strains of the Plasmodium parasite. More than a million people die from malaria each year. (Test your infectious disease IQ.)
P. falciparum is the most virulent of these strains and accounts for nearly 85 percent of all malaria infections. (See a malaria parasite picture.)
Three of the four human strains are known to have originally come from Old World monkeys. The exact origins of P. falciparum have been a mystery.
Researchers had thought that P. falciparum and P. reichenowi—the malaria strain found in chimpanzees—evolved independently from a common ancestor about five to seven million years ago.
But the new study has found that the human strain is actually a mutated form of the chimp strain.
"Current wisdom that P. falciparum has been in humans for millions and millions of years is wrong," said study co-author Nathan Wolfe, director of the Global Viral Forecasting Initiative based in San Francisco, California, and a National Geographic emerging explorer. (The National Geographic Society owns National Geographic News.)
"We now know that there was a point in time when this was primarily a disease in chimpanzees that jumped and took hold in humans."
Just One Jump
The team discovered that the human and chimpanzee strains have certain genetic similarities, but that the chimp strain is more genetically diverse.
Further analysis placed all 133 variants of P. falciparum found around the world under a single branch of the P. reichenowi family tree.
SOURCES AND RELATED WEB SITES