Scientists have long puzzled over the observation that drug-resistant malaria arises more often in southeast Asia than in Africa, which has the world's highest prevalence of the disease. Now, modelling points to competition between malaria strains as a partial explanation for the trend.
Multiple strains of the most dangerous malaria parasite (Plasmodium falciparum) often infect a single person. To examine the parasite’s population dynamics, Mary Bushman at Emory University in Atlanta, Georgia, and her colleagues modelled the origin and spread of drug-resistant varieties.
The researchers found that if malaria is rampant, drug-sensitive parasites in a host's bloodstream quickly outcompete resistant parasites circulating in the same host. But if malaria incidence is low, drug-resistant types are more likely to gain a foothold.
The team also modelled events in an area with high disease burden after a significant number of resistant strains become established. In that scenario, resistant strains can spread rapidly if widespread use of anti-malarial drugs quickly kills off drug-sensitive strains.