Friday, April 15, 2016

Resistance To Antimalarial Drugs Is Not Passed On To Parasite Offspring

The parasites that cause malaria often develop resistance to antimalarial drugs, but according to a new study, parasites with mutations that make them resistant to an antimalarial called atovaquone can’t pass their resistance on to their offspring. The drug disrupts the lifecycles of the parasites while they’re living within their mosquito hosts. Atovaquone, is a component of the antimalarial medication Malarone. It kills both the blood and liver stages of malaria, however researchers believed that it’s prone to resistance like so many other antimalarial medications. To investigate, a team of scientists examined three atovaquone resistant strains of Plasmodium Bergheim, a malarial parasite. Each strain contains a different mutation in their cytB gene, which is encoded in their mitochondrial DNA. The team let mosquitoes infected with the Plasmodium feed on mice infected with the resistant Plasmodium strains, and then they followed the parasites over the course of their entire lifecycle.

While resistance mutations protected the parasites from the drug, it was lethal later on in the mosquito phase. "Two of the mutations resulted in developmental defects in the parasites’ fertilized embryos, and the third mutation led to complete infertility. The team describes cytB mutations as genetic time bombs. Because maternally-inherited mitochondrial DNA is critical for a molecular process that Plasmodium rely on when they’re living inside of mosquitoes, the resistant parasites weren’t able to respire efficiently. Since this severely impairs their reproductive cells, atovaquone-resistant mutations can’t be passed on to the next generation of parasites. " (Goodman)

In a total of 44 separate transmission attempts which involved over 750 mosquito bites, the transmission of atovaquone resistance was observed just once. And this mutation couldn’t be transmitted further despite seven attempts. Cross breeding parasites with and without these mutations didn’t work either, which means we could be one step closer to being able to stop malaria from spreading across the world.

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