THE IMPORTANCE OF SENSITIVE DETECTION OF MALARIA PARASITES IN THE HUMAN AND INSECT HOSTS IN EPIDEMIOLOGIC STUDIES, AS SHOWN BY THE ANALYSISOF FIELD SAMPLES FROM GUINEA-BISSAU

A method based on the polymerase chain reaction (PCR) for highly sensi tive detection and identification of human malaria parasites was appli ed to blood and mosquito samples obtained from a village in Guinea Bis sau. The prevalence of parasites in the human population was shown to be greatly underestimated by microscopical examination. In particular, a high incidence of Plasmodium malariae and P. ovale parasites was re vealed only by the PCR assay. Preliminary evidence was obtained to sho w that the distribution of P. malariae infections within the village w as non-random. This was supported by analysis of the parasite species infecting the mosquito vector. The implication of these results for th e design and interpretation of epidemiological surveys is discussed.