Fast-changing genes help malarial parasites hide in the human body, a new study has revealed.
The study from the Wellcome Trust Sanger Institute revealed that parasites can rapidly change the proteins on the surface of their host cells during the course of a single infection in order to hide from the immune system.
In the study, Plasmodium falciparum parasites were kept dividing in human blood for over a year in the laboratory, with the full parasite genome being sequenced regularly, which gave the scientists snapshots of the parasite's genome at multiple time points, allowing them to track evolution as it unfolded in the lab.
Researchers found that the 60 or so genes that control proteins on the surface of infected human blood cells, known as var genes, swapped genetic information regularly, creating around a million new and unrecognizable surface proteins in every infected human every two days.
First author William Hamilton explained that these genes are like decks of cards constantly being shuffled and the use of whole genome sequencing and the sheer number of samples they collected gave them a detailed picture of how the var gene repertoire changes continuously within red blood cells.
The results show, for the first time, that the process of swapping genetic information, known as recombination, happens not when the malaria parasite is inside the mosquito, as previously thought, but during the asexual stage of the parasite's life-cycle inside human blood cells, which may go some way to explaining how chronic asymptomatic infection, a crucial problem for malaria elimination, is possible.
Researcher Antoine Claessens added that it's very likely that mosquitos are re-infected with Plasmodium falciparum parasites at the beginning of each wet season by biting humans who have carried the parasites, often asymptomatically, for up to eight months during the dry season and during those months the parasite's var genes are busy recombining to create millions of different versions - cunning disguises that mean they remain safe from the immune system and ready for the new malarial season.