Changes in malaria incidence after mass drug administration in Nicaragua.

Mass drug administration (MDA) in 1981 reduced the incidence rates of both Plasmodium vivax and P falciparum infection in Nicaragua. Impact on P vivax cases lasted for four months and on P falciparum for seven. Subtherapeutic primaquine doses, the shorter extrinsic cycle of P vivax in the insect vector, and the timing of MDA at a high-transmission period of the year may explain the limited effects of the campaign. Positive results of the anti-malaria campaign included improvements in case-finding and routine surveillance, the apparent prevention of at least 9200 malaria cases, the training of some 70 000 antimalaria volunteers, and the participation of about 70% of the population in anti-malarial activities.