Parasites and poverty: the case of schistosomiasis

Abstract

Simultaneous and sequential transmission of multiple parasites, and their resultant overlapping chronic infections, are facts of life in many underdeveloped rural areas. These represent significant but often poorly measured health and economic burdens for affected populations. For example, the chronic inflammatory process associated with long-term schistosomiasis contributes to anaemia and undernutrition, which, in turn, can lead to growth stunting, poor school performance, poor work productivity, and continued poverty. To date, most national and international programs aimed at parasite control have not considered the varied economic and ecological factors underlying multi-parasite transmission, but some are beginning to provide a coordinated approach to control. In addition, interest is emerging in new studies for the re-evaluation and recalibration of the health burden of helminthic parasite infection. Their results should highlight the strong potential of integrated parasite control in efforts for poverty reduction.

Figure 1

Proposed vicious cycle of schistosomiasis in the presence of poverty. Left arrow-- Poverty reduces water use options and increases risk of infection, while also influencing personal adaptation and coping for disease syndromes caused by infection. Right arrow-- Increased disability, related to the impact of chronic and recurrent infection, reduces productivity and perpetuates poverty.

Figure 2

Features of the rural poverty trap, in which all of the household's capital must be invested each year in order to survive. On average each year, the family just breaks even. Because of continued depreciation of physical capital (tools, soil quality, etc.) and increasing family numbers, per capita income tends to fall each year.

Figure 3a

Global distribution of severe poverty, measured as proportion of national population earning less that 1 US Dollar per day. Data are from the World Bank for 2000, or the most recent values prior to 2000.

Figure 3b

Distribution of human schistosomiasis; shading intensity indicates the number of cases per country in 2000, ranging from less than 200,000 (unshaded) to over 10 million cases per country (darkest shading), based on WHO estimates (Chitsulo et al., 2000)

Figure 4

Environmental features and human behaviour strongly tie Schistosoma transmission to certain locales, and embed the disease caused by infection into the pattern of rural life.