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Scientists have come up with a new hypothesis about the evolution of hundreds of species of malaria—including the one that is dangerous for people.

Extensive testing of malarial DNA found in birds, bats, and other small mammals from five East African countries shows malaria has its roots in bird hosts—and then spread to bats and on to other mammals.

“We can’t begin to understand how malaria spread to humans until we understand its evolutionary history,” says lead author Holly Lutz, a doctoral candidate in ecology and evolutionary biology and population medicine and diagnostic sciences at Cornell University. “In learning about its past, we may be better able to understand the effects it has on us.”

Malaria is an ancient parasitic single-celled organism that reproduces in the bloodstream of its host and is transferred between hosts by blood-feeding insects, such as mosquitoes.

Different species of malaria live in different species of host animals. Malaria affects approximately 800 million people every year, primarily in tropical and subtropical regions in more than 100 countries. Malaria was eradicated in the United States in the 1950s.

For the new study, published in the journal Molecular Phylogenetics and Evolution, researchers took blood samples from hundreds of East African birds, bats, and other small mammals and screened the blood for the parasites.

When they found malaria, they took samples of the parasites’ DNA and sequenced it to identify mutations in the genetic code. From there, they determined how different malaria species are related based on differences in their genetic code. Having large sample sizes from many species was key to the findings.

“Trying to determine the evolutionary history of malaria from just a few specimens would be like trying to reconstruct the bird family tree when you only know about eagles and canaries,” Lutz says. “There’s still more to discover, but this is the most complete analysis of its kind for malaria to date.”

Humans can’t contract malaria directly from birds or bats. And while the study doesn’t have direct implications for malaria treatment in humans, it may clarify what’s ahead.

“Malaria is notoriously adaptive to treatment, and its DNA holds a host of secrets about how it’s able to change and evolve,” says coauthor and Field Museum Curator of Mammals Bruce Patterson. “Having a better understanding of its evolutionary history could help scientists anticipate its future.”

Source: Cornell University