Intensity of malaria transmission and the spread of Plasmodium falciparum resistant malaria: a review of epidemiologic field evidence.

Malaria transmission intensity has been proposed, based on theoretical models, as an important factor for the spread of falciparum-resistant malaria, but the predictions obtained vary according to the assumptions inherent in the model used. We summarized the available field data on transmission intensity and the prevalence of malaria drug resistance. Resistance to chloroquine and sulphadoxine-pyrimethamine monotherapy was invariably higher where transmission was intense. Vector control interventions were associated with a better chloroquine and sulfadoxine-pyrimethamine efficacy. However, high resistance to chloroquine and also to combination therapy (chloroquine plus sulphadoxine-pyrimethamine and amodiaquine plus sulfadoxine-pyrimethamine) was also observed in very low transmission areas. Reducing transmission intensity is likely to slow the spread of drug resistance. Nevertheless, where transmission is extremely low, to limit the unnecessary use of antimalarials and a consequent paradoxical acceleration of the spread of resistance, patients should be treated only after laboratory confirmation of malaria.