Data from: Parasite genetic variation for in vivo susceptibility to anti-malarial drugs: implications for treatment efficacy and resistance monitoring

For malaria parasites, artemisinin-based drugs are the frontline weapon in the fight against disease, but reports from the field of slower parasite clearance rates during treatment are generating concern that the useful lifespan of these drugs may be limited. In the absence of molecular markers for resistance, current efforts to monitor drug efficacy are based on the rate at which parasites are cleared from infections. However, some knowledge of the standing variation in parasite susceptibility is needed in order to identify a meaningful increase in infection half-life. Here we show that five previously unexposed genotypes of the rodent malaria parasite Plasmodium chabaudi differ substantially in their in vivo response to treatment. Slower clearance rates were not linked to parasite virulence or growth rate, going against the suggestion that drug treatment will drive the evolution of virulence in this system. The level of variation observed here in a relatively small number of genotypes suggests existing ‘resistant’ parasites could be present in the population and therefore increased parasite clearance rates could represent selection on pre-existing variation rather than de-novo resistance events. This has implications for resistance monitoring as susceptibility may depend on evolved traits unrelated to drug exposure.