Malaria in soldiers returning from Vietnam. Epidemiologic, therapeutic, and clinical studies.

Abstract

Malaria occurring in the U. S. A. among Army troops who returned from Vietnam in 1966 and 1967 was investigated epidemiologically and clinically. The incidence of malaria among returnees in the U. S. A. varied from 0.11 to 4.66% per year; rates of hospitalization for malaria for the same troops during their service in Vietnam varied from 2.3 to 4.8% per year. Infections with Plasmodium falciparum were rare in the U. S. A. but frequent in Vietnam. Clinically manifest vivax infections occurred significantly less often in Negro than in white men, which appeared to be due to natural resistance of the Negro. The 8-week CP regimen (300 mg chloroquine base plus 45 mg primaquine base once a week for 8 weeks), when used under field conditions as radical cure treatment of clinically manifest vivax malaria acquired in Vietnam, was associated with a 22.3% relapse rate. The disappointing results were due, at least in part, to failure of patients to complete the regimen. A significantly lower relapse rate (7%) was achieved with the easily supervised regimen of 15 mg primaquine base daily for 14 days. The secondary exoerythrocytic forms of Vietnam strains of Plasmodium vivax appear less susceptible to primaquine than those of Korean strains but more susceptible than those of the Chesson strain.