FECAL EGG AGGREGATION IN HUMANS INFECTED WITH SCHISTOSOMA-JAPONICUM IN CHINA

In this study we examine the variation in Schistosoma japonicum egg co unts caused by differences in worm loads between individuals and the v ariability of egg counts within individuals with a given worm load. Si x villages were selected from an area moderately endemic for Asian sch istosomiasis in the Dongting Lake region (Hunan province), China. From a total population of 3451 individuals (53.8% male; (x) over bar = 31 years), 163 subjects were identified as consistently stool egg-positi ve based on three successive positive Kato-Katz (KK) smears (41.67 mg/ smear) obtained from one stool specimen. The distribution of eggs amon g individuals was found to be strongly aggregated (k = 0.27), but the distribution within the three smears was found to be only slightly agg regated (k = 2.59), indicating only minor clustering of eggs in stools . The relatively slight clustering of eggs within stool specimens sugg ests that a single KK smear may be quite adequate for detecting indivi duals moderately to heavily infected (>100 eggs/g stool (epg)), as nee ded for a strategy of morbidity control. However, for estimating the t rue prevalence of infection in a community, or for obtaining an accura te estimate of egg excretion for research studies, multiple KK smears are warranted. (C) 1998 Elsevier Science B.V. All rights reserved.