Plasmodium Ovale in Liberia

Abstract
Summary A total of 94 infections with P. ovale have been examined in Liberia. Of these, 16 cases have been diagnosed in thick blood films only and 78 cases have been diagnosed in thin blood films. In 18 cases the diagnosis was confirmed by production of the oval host erythrocyte by quick-drying of thin blood films. One infection which showed features of both P. ovale and P. vivax and one infection with P. vivax have been examined. In surveys, P. ovale was found at a rate of 4.4 per cent in the total population, 9 per cent in the age group 5–15 years, and 10 per cent in the age group 1–4 years. The morphology of P. ovale and its host erythrocyte, together with the association of Schüffner's dots with older parasites, were the main criteria used for identification; a relationship was demonstrated between atmospheric humidity and the occurrence of oval host erythrocytes in thin blood films. Epidemiological surveys indicate an overall rate of 4–5 per cent of P. ovale infections in Liberia, with a seasonal peak between December and March, beginning some 2 months after the cessation of the rains, when the incidence of P. malariae is high and that of P. falciparum is low. The relative insusceptibility of West African Negroes to P. vivax is judged the main reason for the absence or rarity of that parasite over large areas.

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