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Mixed-strain malaria infections influence drug resistance

A boy awaits treatment at a malaria clinic in Myanmar. Resistance to the one remaining drug for the most lethal species of malaria parasite, Plasmodium falciparum, has emerged in Southeast Asia.

Scientists have documented for the first time how competition among different malaria parasite strains in human hosts could influence the spread of drug resistance.

“We found that when hosts are co-infected with drug-resistant and drug-sensitive strains, both strains are competitively suppressed,” says Mary Bushman, lead author of the study and a PhD candidate in Emory University’s Population Biology, Ecology and Evolution Graduate Program. “Anti-malarial therapy, by clearing drug-sensitive parasites from mixed infections, may result in competitive release of resistant strains.”

Proceedings of the Royal Society B published the research, led by the labs of Jaap de Roode, an evolutionary biologist at Emory, and Venkatachalam Udhayakumar, a malaria expert from the Centers of Disease Control and Prevention’s Division of Parasitic Diseases and Malaria.

Almost half of the world’s population is at risk for malaria, a complex disease caused by five species of Plasmodium parasites that are transmitted to humans by 30 to 40 different species of mosquitoes that all behave differently. The current study focused on Plasmodium falciparum, the most common malaria parasite on the continent of Africa and the one responsible for the most malaria-related deaths globally.

P. falciparum has developed resistance to former first-line therapies chloroquine and sulfadoxine-pyrimethamine. “We’re now down to our last treatment, artemisinin combination therapy, or ACT, and resistance to that recently emerged in Southeast Asia,” Bushman says. “If ACT resistance continues to follow the same pattern, the world may soon be without reliable antimalarial drugs.”

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