Summary
The prevalence of chloroquine-resistant Plasmodium falciparum malaria isolated from 39 individuals living in 16 localities in the Brazilian Amazon was determined. Defibrinated blood samples from each patient were placed in vials containing a 0.5% solution of glucose with or without chloroquine and incubated in a constant temperature chamber at 39-40°C. After a 24 h incubation period, P. falciparum trophozoites developed to schizonts in control vials (without chloroquine) and in 100%; 87.1%; 28.2%; 15.3% and 7.6% of culture samples containing 0.5; 1.0; 2.0; 3.0 and 4.0 nanomols of chloroquine/ml of blood, respectively. Resistant P. falciparum strains were found in all locations studied indicating a broad distribution of chloroquine resistant falciparum malaria in the Amazon basin.