Individual and village‐level study of water contact patterns and Schistosoma japonicum infection in mountainous rural China

Abstract

Summaryobjective To describe the exposure patterns related to schistosomiasis transmission in 10 villages in rural Xichang County, Sichuan, China. methods Individual and village-level study of water contact exposure and Schistosoma japonicum reinfection; after initial infection survey and treatment, reinfection was determined 2 years later for 1604 individuals, of whom 578 also participated in a cross-sectional survey to assess their water contact behaviours.results The highest intensity of reinfection was observed in farmers aged 20-29 years, with no difference between sexes. While water contact measured as m 2 -minutes of contact was not associated with reinfection, an exposure metric computed by spatially weighting water contact by cercarial risk was correlated with both infection status and intensity. Village-level indicators based on snail density, number of infected snails, mouse bioassay data, and averaged individual-level exposures were associated with village reinfection rates.conclusion Age-acquired immunity may be present in this population, but the study lacked sufficient power to discern differences in the exposure infection relationship with age.

Exploring the Contribution of Host Susceptibility to Epidemiological Patterns of Schistosoma japonicum Infection Using an Individual-Based Model

“…Both in our earlier epidemiological studies and those of others, infection intensity was found to be relatively insensitive to degree of water contact. 27,33 This was also the case in these simulation studies (see Supplemental Material Item 8 [SM8]). Hence, in the simulations, and very likely in the field, cercarial density and individual susceptibility are the principal determinants of the population distribution of EPG and of prevalence.…”

“…The survey design details are presented elsewhere. 27,28 Because we are not here interested in seasonality but in year-end infection intensity, each individual was assigned a constant time-weighted average water contact value over the annual infection season as detailed further in Supplemental Material Item 1 (SM1).…”

Schistosomiasis japonica: Modelling as a tool to explore transmission patterns

“…Regression models are chiefly used to extract risk factors that can possibly influence schistosomiasis transmission, logistic regression in particular. The results reveal that risk factors relative to schistosomiasis infection/re-infection mainly include water-contact, individual immunity, past history of S. japonicum infection, which to some extent depend on the prevailing socioeconomic situation, education level, age, occupation and residence (Gray et al, 2009;Ross et al, 1998aRoss et al, , 1998bRoss et al, , 1998cRoss et al, , 1997aSeto et al, 2007;Tan et al, 2004;Yang et al, 2009;Zhang et al, 1997;Zhu et al, 2011). Factors relative to the disability weight of chronic schistosomiasis are chiefly clinical signs, such as abdominal pain, diarrhoea, hepatomegaly and hepatic fibrosis as well as impaired capacity for work or study, which varies with age, occupation and intensity of infection Li et al, 1993;Xu et al, 2009;Zhou et al, 2005).…”

Model approaches for estimating the influence of time-varying socio-environmental factors on macroparasite transmission in two endemic regions

“…The latter was estimated using standard techniques (Lund and Browder 1944; Mosteller 1987), while the frequency and duration of activities was estimated in the two study regions by questionnaire that asked residents about water contact related to 8 activities each month. The Xichang questionnaire, administered to a 25% sample of residents in 20 villages in 2000, has been described elsewhere (Spear, Seto et al 2004; Seto 2007). In Changqiu, the same questionnaire was administered to residents in 7 villages in 2006 (total surveyed populations n XC =968 and n CQ =360).…”