Prevalence of Chloroquine-Resistant Falciparum Malaria in the Brazilian Amazon

José J. FerraroniInstituto Nacional de Pesquisas da Amazonia (INPA) and Universidade do Amazonas (Instituto de Medicine Tropical de Manaus), Department of Microbiology, University of Montana, Department of Preventive Medicine and Community Health, Texas Tech University Health Sciences Center, Department of Parasitology, School of Medicine, Gunma University, Manaus, Brazil

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Clarence A. SpeerInstituto Nacional de Pesquisas da Amazonia (INPA) and Universidade do Amazonas (Instituto de Medicine Tropical de Manaus), Department of Microbiology, University of Montana, Department of Preventive Medicine and Community Health, Texas Tech University Health Sciences Center, Department of Parasitology, School of Medicine, Gunma University, Manaus, Brazil

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Jack HayesInstituto Nacional de Pesquisas da Amazonia (INPA) and Universidade do Amazonas (Instituto de Medicine Tropical de Manaus), Department of Microbiology, University of Montana, Department of Preventive Medicine and Community Health, Texas Tech University Health Sciences Center, Department of Parasitology, School of Medicine, Gunma University, Manaus, Brazil

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Mamoru SuzukiInstituto Nacional de Pesquisas da Amazonia (INPA) and Universidade do Amazonas (Instituto de Medicine Tropical de Manaus), Department of Microbiology, University of Montana, Department of Preventive Medicine and Community Health, Texas Tech University Health Sciences Center, Department of Parasitology, School of Medicine, Gunma University, Manaus, Brazil

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The prevalence of chloroquine-resistant falciparum malaria was determined for humans living at 28 different sites in the Brazilian Amazon. Blood samples obtained from each patient were defibrinated, placed in vials containing 0.5% glucose and or chloroquine and incubated for 24 hours at 39–40°C without agitation. In vitro sensitivity of the parasite to four different concentrations of chloroquine was determined for each sample. After 24 hours of incubation, trophozoites of Plasmodium falciparum developed to schizonts in all control cultures (no chloroquine) as well as in 80.6, 48.4, 11.8 and 7.5% of the cultures containing 0.5, 1.0, 2.0, and 3.0 nmol chloroquine/ml blood, respectively. Chloroquine-resistant P. falciparum was found in blood samples from all 28 locations, indicating that such resistance is widely spread in the Brazilian Amazon.

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