Plasmodium vivax Infections in U.S. Army Troops: Failure of Primaquine to Prevent Relapse in Studies from Somalia

Bonnie L. Smoak Division of Preventive Medicine and Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Tropical Disease Unit, The Toronto Hospital, Washington, District of Columbia, Canada

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Robert F. DeFraites Division of Preventive Medicine and Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Tropical Disease Unit, The Toronto Hospital, Washington, District of Columbia, Canada

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Alan J. Magill Division of Preventive Medicine and Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Tropical Disease Unit, The Toronto Hospital, Washington, District of Columbia, Canada

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Kevin C. Kain Division of Preventive Medicine and Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Tropical Disease Unit, The Toronto Hospital, Washington, District of Columbia, Canada

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Bruce T. Wellde Division of Preventive Medicine and Division of Communicable Diseases and Immunology, Walter Reed Army Institute of Research, Tropical Disease Unit, The Toronto Hospital, Washington, District of Columbia, Canada

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Different strains of Plasmodium vivax vary in their sensitivity to primaquine, the only drug that prevents relapses. Described are the clinical data and relapse pattern for 75 soldiers treated for vivax malaria since returning from Somalia. Following their initial attack of malaria, 60 of the 75 cases received a standard course of primaquine (15 mg base daily for 14 days). Twenty-six of the 60 soldiers subsequently relapsed for a failure rate of 43%. Eight soldiers had a second relapse following primaquine therapy after both the primary attack and first relapse. Three of these soldiers had received a higher dosage of primaquine (30 mg base daily for 14 days) after their second attack. The apparent ineffectiveness of primaquine therapy in preventing relapses suggests the presence of primaquine-resistant* P. vivax strains in Somalia.

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