Epidemiological identification of Chinese individuals putatively susceptible or insusceptible to Schistosoma japonicum: a prelude to immunogenetic study of human resistance to Asian schistosomiasis

Author： Ross A. G. P. Sleigh A. C. Williams Y. S. Li G. M. Waine Y. Li G. J. Tang G. T. Forsyth S. J. Mcmanus D. P.

Publisher： Routledge Ltd

ISSN： 1364-8594

Source： Annals of Tropical Medicine and Parasitology, Vol.92, Iss.7, 1998-10, pp. : 765-774

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Abstract

An epidemiological method, field-tested in Hunan, China, to identify residents potentially susceptible or insusceptible to endemic schistosomiasis japonica is described, as a prelude to selection of subjects for immunogenetic studies. After an initial cross-sectional survey on two islands (Qingshan and Niangashanpopulation 2990) in 1995-1996, an informative cohort (N = 249) was selected for treatment and 9-month follow-up to measure exposure and re-infection. Both the population prevalence (15.8%) and the geometric mean intensity of infection (26.2 eggs/g faeces) indicated that the islands were moderately endemic for schistosomiasis. Exposure measurements revealed a strong, positive, linear association (r = 0.70) between daily activity diaries and direct water-contact observation. Individuals identified as stool-positive for schistosomiasis had significantly more water contact than those who were egg-negative (P = 0.03). Almost all (93%) of the cohort had ultrasonographic evidence of periportal fibrosis before treatment but in only 1.2% was this fibrosis scored 1 in terms of the stages identified by the World Health Organization. At the follow-up it was possible to classify the 249 subjects into three, distinct, exposure-infection epidemiological groups. The first group (N = 20) was susceptible to re-infection and constituted 8% of the cohort. The second group (N = 61) was apparently insusceptible to re-infection despite the continuing high levels of exposure and included 24% of the cohort. The other 68% of the cohort (N = 168) remained uninfected but were at most only moderately exposed, or had a status indeterminate due to non-compliance. This epidemiological identification of susceptibles and insusceptibles for schistosomiasis japonica links field and ongoing laboratory studies aimed at characterising the genetic and immunological factors associated with resistance to re-infection and/or disease.