In brief
Malaria parasites being released from a red blood cell, MedicalRF.com
Malaria around longer than previously thought Researchers from the University of Missouri–St. Louis have
Ricklefs and Outlaw’s research suggests these parasites
discovered a way to better determine the evolutionary time-
jump to new, unrelated hosts at any time.
line for microscopic malaria parasites.
By marrying DNA research to a new statistical approach,
Gaining a better understanding of the origins of pathogenic
the researchers got a better handle on the timeline of lineages is fundamental to understanding emerging diseases, parasite evolution. They found a key gene in the malaria according to the researchers. For example, it’s been difficult parasites evolved at 60 percent of the rate of the same to pin down when falciparum malaria (the most dangerous form of the parasite to humans) originated in our species; current estimates range from 10,000 years to several million years. Robert Ricklefs, Curators’ Professor of Biology at UMSL, and Diana Outlaw, a former UMSL postdoctoral fellow, wrote the paper “A Molecular Clock for Malaria Parasites,” which was published July 9 in Science Magazine. “Because the single-cell malaria parasites leave no fossil record, one has to estimate their rate of evolution by com-
gene in their hosts. Knowing the gene evolution rate of the vertebrate hosts, Ricklefs and Outlaw were able to estimate that modern malaria parasites began to diversify across mammals, birds and reptiles about 16 million years ago, while human ancestors gained the parasite about 2.5 million years ago. Previous studies have suggested that malaria appeared in humans between 4,000 and 10,000 years ago.
parison with their hosts," Ricklefs says. “Previously, this
Ricklefs says, “Malaria parasites undoubtedly were
had been done under the assumption that parasites evolve
relatively benign for most of that history, becoming a
at the same rate as their hosts and thus were the same
major disease only after the origins of agriculture and
age as their hosts.”
dense human populations.”
4