Abstract
BackgroundFew studies have described heterogeneity in Schistosoma japonicum infection intensity, and none were done in Philippines. The purpose of this report is to describe the village-to-village variation in the prevalence of two levels of infection intensity across 50 villages of Samar Province, the Philippines.MethodsThis cross-sectional study was conducted in 25 rain-fed and 25 irrigated villages endemic for S. japonicum between August 2003 and November 2004. Villages were selected based on irrigation and farming criteria. A maximum of 35 eligible households were selected per village. Each participant was asked to provide stool samples on three consecutive days. All those who provided at least one stool sample were included in the analysis. A Bayesian three category outcome hierarchical cumulative logit regression model with adjustment for age, sex, occupation and measurement error of the Kato-Katz technique was used for analysis.ResultsA total of 1427 households and 6917 individuals agreed to participate in the study. A total of 5624 (81.3%) participants provided at least one stool sample. The prevalences of those lightly and at least moderately infected varied from 0% (95% Bayesian credible interval (BCI): 0%–3.1%) to 45.2% (95% BCI: 36.5%–53.9%) and 0% to 23.0% (95% BCI: 16.4%–31.2%) from village-to-village, respectively. Using the 0–7 year old group as a reference category, the highest odds ratio (OR) among males and females were that of being aged 17–40-year old (OR = 8.76; 95% BCI: 6.03–12.47) and 11–16-year old (OR = 8.59; 95% BCI: 4.74–14.28), respectively. People who did not work on a rice farm had a lower prevalence of infection than those working full time on a rice farm. The OR for irrigated villages compared to rain-fed villages was 1.41 (95% BCI: 0.50–3.21).DiscussionWe found very important village-to-village variation in prevalence of infection intensity. This variation is probably due to village-level variables other than that explained by a crude classification of villages into the irrigated and non-irrigated categories. We are planning to capture this spatial heterogeneity by updating our initial transmission dynamics model with the data reported here combined with 1-year post-treatment follow-up of study participants.
Highlights
Few studies have described heterogeneity in Schistosoma japonicum infection intensity, and none were done in Philippines
Reasons given for non-inclusion of households were ineligible households (51.5%), refusal to participate (15.2%), the household members were not permanent residents of the village (12.9%), the household members migrated elsewhere (11.4%), no one could be reached after at least 3 attempts (6.1%) and the household head lived outside the home (3.0%)
The proportions of male participants who provided at least one stool sample was 52.8% and 56.1% among those who did not provide any stool sample
Summary
Few studies have described heterogeneity in Schistosoma japonicum infection intensity, and none were done in Philippines. The purpose of this report is to describe the village-to-village variation in the prevalence of two levels of infection intensity across 50 villages of Samar Province, the Philippines. The life cycle of S. japonicum includes an amphibious snail of Oncomelania species and a mammalian definitive host, including humans or other animal reservoirs. Unlike other species of schistosomes, animal reservoirs are thought to contribute significantly to the transmission and maintenance of life cycle of S. japonicum in areas where it is endemic [2]. Rice farming and annual rainfall patterns in these endemic areas maximize contact among humans, animal reservoirs and freshwater infested with Oncomelania snails which in turn increase the risk of infection [2,3]. According to the severity of histopathology and intensity of infection, S. japonicum is thought to be more pathogenic than the other schistosomes [4,5,6]
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