A socioeconomic approach to the control of Schistosoma mansoni in St. Lucia

Systematic observations of man/water contact in a valley endemic for S. mansoni in St. Lucia were carried out prior to the introduction of a household water supply. The observations indicated that exposure of the population to cercaria-infested rivers and streams could be broken down into different types related to distinct and measurable domestic and economic activities. The number and duration of daily contacts with water played an important role in determining the relative risk of infection and correlated significantly with the number of infected persons by age in a survey conducted immediately following the observations. Consideration should be given to measuring and assessing the relative importance of different activities involving contact with water in relation to transmission and the formulation of control strategies.(AU)

The social ecology of a disease: the study of an S. Mansoni control programme in the West Indies (St. Lucia)

This thesis is concerned with a sociological-anthropological assessment of an S. mansoni control programme in an endemic area in the West Indies (St. Lucia) in which an experiment has been carried out to compare different methods of control-mollusciciding, engineering, and chemotherapy. The theoretical basis of the experiment is a model developed by G. Macdonald in which the S. mansoni transmission cycle is sustained by the interaction of the human and biological population. For the human population there is a threshold level of exposure (called by Macdonald the 'break-point') below which transmission will discontinue, and above which the host and parasitic population are in equilibrium. Similarly there is a population density both of worm pairs within the human host, and of the snail intermediate host, below which the transmission will also stop. The objective of the control programme has been to reduce transmission below this threshold by, (a) destroying snail populations (mollusciciding), (b) killing worm pairs in the host (chemotherapy), and (c) reducing human exposure (engineering-the installation of household water to prevent contact with contaminated water-bodies). Because of rapidly changing socio-economic conditions in St. Lucia disturbing any equilibrium between host and parasite, the model is not relevant. The results of the experiment to date indicate that the technological bias inherent in this model has not enabled the experimenters to control the disease effectively by means of mollusciciding or chemotherapy. In the attempt to reduce human exposure, however, there has been significant reduction in incidence as a result of the introduction of household water, but only when supplemented by a water-contact study and a health education programme, suggesting that social and cultural systems play a dominant role in the cycle in this area. It is concluded that, (a) it is possible to assess, measure and control the exposure of human population to contaminated water bodies in an S. mansoni endemic area, (b) it is the daily, weekly and seasonal cycles of human activity that are dominant within the transmission cycle, and can explain variations in the incidence and prevalence of the disease, (c) there appear to be upper limits to the intensity of an S. mansoni infection, though there is no clear indication that this has lasting effects, (d) for a control programme to be ensured of success there should be preliminary sociological-anthropological investigations to discern the social and cultural factors influencing the transmission cycle, and account should be taken of the socio-economic context in which any control programme is taking place(AU)

Reduced contact with natural water bodies through provision of water supplies in an S. Manson endemic area - abstract

Water supplies are being installed in an area where there is a high prevalence of S. mansoni in an endeavour to determine the efficacy of this method of schistosomiasis control. The rural water system incorporates the supply of water to each household, laundry and shower units, and a simple swimming pool. In the first settlement in which water has been made available, post-control water contact studies show that compared with pre-control data, contact with natural water bodies has been reduced by approximately 80 percent. Further studies are being made to obtain parasitological evidence that this is reducing the incidence and prevalence of S. mansoni (AU)