DEVELOPMENT AND LABORATORY EVALUATION OF A POLYMERASE-CHAIN-REACTION FOR MONITORING SCHISTOSOMA-MANSONI INFESTATION OF WATER

A sensitive and specific detection of cercariae of human schistosomes is required for better definition of risk of infection. In the present study, we have developed a polymerase chain reaction (PCR) assay for the detection of cercariae of Schistosoma mansoni in water. A simple D NA preparation was adapted for this purpose, and PCR primers were desi gned based on the 121-basepair highly repeated sequence we previously identified in the genome of S. mansoni. The PCR assay detected as litt le as 10(-6) ng of S. mansoni DNA, and the high sensitivity enabled th e detection of a single cercaria. For trapping of cercariae we adapted a filtration apparatus previously used for separating schistosome egg s from turbid enzymatic digests of tissues. A single cercaria could be detected in repeated tests of water filtrates. Since the target DNA i s tandemly arranged, a ladder pattern of the PCR products was demonstr ated. A direct relationship was demonstrated between the number of lad der bands of the amplification products, and DNA concentration or numb er of cercariae. The feasibility of semiquantitation of schistosome la rvae in natural water was thus suggested. The potential of the procedu res described here for epidemiologic studies is discussed.