Data from: Within-host competition and drug resistance in the human malaria parasite Plasmodium falciparum

Infections with the malaria parasite Plasmodium falciparum typically
comprise multiple strains, especially in high-transmission areas where
infectious mosquito bites occur frequently. However, little is known about
the dynamics of mixed-strain infections, particularly whether strains
sharing a host compete or grow independently. Competition between
drug-sensitive and drug-resistant strains, if it occurs, could be a
crucial determinant of the spread of resistance. We analyzed 1,341 P.
falciparum infections in children from Angola, Ghana, and Tanzania and
found compelling evidence for competition in mixed-strain infections:
overall parasite density did not increase with additional strains, and
densities of individual strains (chloroquine-sensitive and
chloroquine-resistant) were reduced in the presence of competitors. We
also found that chloroquine-resistant strains exhibited low densities
compared to chloroquine-sensitive strains (in the absence of chloroquine),
which may underlie observed declines of chloroquine resistance in many
countries following retirement of chloroquine as a first-line therapy. Our
observations support a key role for within-host competition in the
evolution of drug-resistant malaria. Malaria control and
resistance-management efforts in high-transmission regions may be
significantly aided, or hindered, by the effects of competition in
mixed-strain infections. Consideration of within-host dynamics may spur
development of novel strategies to minimize resistance while maximizing
the benefits of control measures.