THURSDAY, SEPTEMBER 29, 2016

Study finds malaria parasites hide from immune system

A study has found that malaria parasites essentially can hide from the immune system, the Wellcome Trust Sanger Institute said.

The research shows that the parasites, when in red blood cells, rapidly change the proteins on the surface of their host cells during the course of one single infection to go undetected.

"These genes are like decks of cards constantly being shuffled," study co-author William Hamilton said. "The use of whole genome sequencing and the sheer number of samples we collected gave us a detailed picture of how the var-gene repertoire changes continuously within red blood cells."

The findings, which contradict previous theories about the Plasmodium falciparum parasite's life cycle, also may explain how many attempts to create an effective vaccine have failed and how the parasites have been shown to survive in the human body for long periods of time.

As part of the study, the malaria parasites kept dividing in human blood for over a year, with the full parasite genome being sequenced on a regular basis, which gave the scientists snapshots of the parasite's genome at multiple time points, allowing them to track the parasite’s progression. What the researchers discovered was that approximately 60 var genes traded genetic information regularly, which in turn created around a million new and unrecognizable surface proteins in every infected human every 48 hours.

"It's very likely that mosquitoes 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," another co-author, Dr. Antoine Claessens, said. "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."

Further work is planned to fully understand the mechanism driving the recombination of Plasmodium falciparum's var genes and the rate at which it happens.