The research suggests that drugs may unintentionally encourage more harmful strains to evolve because the treatments are more effective at killing milder strains of the disease.
Researchers say that this gives severe strains an advantage – they can survive better in the host and spread to mosquitoes, which pass on the infection to new hosts.
Over time this could mean that people with malaria, when untreated, suffer more harm from their disease.
The research also found that a commonly used malaria drug called artemisinin reduces the advantage that severe strains have over mild strains.
Experts say that careful choice of drugs to treat malaria could minimise the spread of more severe parasite strains.
Dr Petra Schneider of the University of Edinburgh’s School of Biological Sciences said: “Drug treatment for malaria infections is very important and our results suggest that careful choice of drugs and treatment regimens could minimise unexpected consequences. The next step is to determine whether our findings in mice apply to malaria in humans.”
The study by the University of Edinburgh and Pennsylvania State University was carried out in mice and is published in Proceedings of the Royal Society B and is supported by the Wellcome Trust.
Uni of Edinburgh