WASHINGTON: A new Field Museum research has revealed the evolution of malaria all the way back to its original bird host, suggesting that bats are not to be blamed for its spread.
Lead author Holly Lutz from the Cornell University said, "We can't begin to understand how malaria spread to humans until we understand its evolutionary history. In learning about its past, we may be better able to understand the effects it has on us."
Malaria is a parasitic single-celled organism that reproduces in the bloodstream of its host and is transferred between hosts by insects like mosquitos. Different species of malaria live in different species of host animals. Lutz and her colleagues took blood samples from hundreds of East African birds, bats, and other 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, Lutz was able to perform what is called "phylogenetic analyses" to determine how different malaria species are related.
In analyzing the genetic codes of the malaria parasites, Lutz was able to find places where the DNA differed from one species to the next. Then, the scientists used powerful computing software to determine how the different species evolved and how they're related to each other.
This phylogenetic analysis relied on large sample sizes and DNA from many different host species of bats and birds, because otherwise, the picture would be incomplete, “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,” explained Lutz. “There's still more to discover, but this is the most complete analysis of its kind for malaria to date.”
The analysis revealed that malaria has its roots in bird hosts, from which it spread to bats, and then on to other mammals. But Lutz notes that bats aren't the bad guys here.
"It's not that bats are spreading malaria, we get different species of malaria than they do, and we can't get it from them," explained Lutz. "Instead, by looking at patterns of mutations in the DNA of the different malaria species, we're able to see when it branched off from one host group into another. It started out as a parasite in birds, and then it evolved to colonize bats, and from there, it's evolved to affect other mammals."
The study is published in Molecular Phylogenetics and Evolution.