Some Quantitative Aspects of Diagnosis and Epidemiology in Schistosomiasis Mansoni

Kurt KloetzelDepartment of Tropical and Infectious Diseases, Hospital das Clinicas, and Department of Parasitology, University of Sao Paulo Medical School, Brazil

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Oviposition of Schistosoma mansoni is very low, around 250 eggs per day. Since these are deposited in the small veins of the portal system, an estimated 80% being retained in the tissues, diagnosis of schistosomiasis by a stool examination succeeds only when the worm load exceeds a few hundred flukes.

The author presents prevalence data for a highly endemic area in northeastern Brazil and shows how accuracy depends closely on the method of examination used and the number of slides read. When a group of young children is to be studied, it is suggested that the intradermal test be used.

Severity of clinical schistosomiasis probably depends on the worm load. Some individuals with splenomegaly will be host to thousands of flukes. Since the majority of adults in the hyperendemic regions of Brazil have stools positive for S. mansoni, it is suggested that the detection of areas deserving priority in public health measures be judged not by prevalence but by a study of egg counts.