The global epidemiological situation of schistosomiasis and new approaches to control and research

Abstract

While the distribution of schistosomiasis has changed over the last 50 years and there have been successful control programmes, the number of people estimated to be infected or at risk of infection has not been reduced. Today, 85% of the number of infected people are estimated to be on the African continent where few control efforts are made. In terms of disease burden, there is therefore a growing discrepancy between sub-Saharan Africa and the rest of the world. WHO has now developed a dual strategy for the control of schistosomiasis: a strategy for morbidity control adapted to the public health context in high burden areas, and a strategy to consolidate control in areas where a low endemic level has been reached and elimination may be feasible. Related to this new vision, some research needs are pointed out.

Introduction

Schistosomiasis remains one of the most prevalent parasitic infections in the world. It is endemic in 76 countries and territories, and continues to be a global public health concern in the developing world. Because it is a chronic insidious disease, it is poorly recognised at early stages, and becomes a threat to development as the disease disables men and women during their most productive years. It is particularly linked to agricultural and water development schemes. It is typically a disease of the poor who live in conditions which favour transmission and have no access to proper care or effective prevention measures.

The 1984 WHO Expert Committee on the Control of Schistosomiasis introduced a strategy for morbidity control, which had become feasible because of the availability of effective and safe single dose drugs (WHO, 1985). This created high hopes for success, not only in terms of a reduction in the burden of this disease, but also in terms of possible elimination of the infection through a presumed effect of regular treatment on transmission. Community wide treatment campaigns were initiated in numerous endemic areas. Because of the high drug prices, active diagnosis and treatment was the most cost-effective and thus preferred strategy. After an initial ‘attack phase’ involving substantial, often external funds, it was expected that the endemic level would have decreased to an extent that national health authorities would be able to take over implementation during a maintenance phase.

Whereas a number of countries have managed to sustain schistosomiasis control over the last two decades, most donor-funded vertical control initiatives set up in Africa during the 1980s have shown to be unsustainable. Despite the fact that the 1991 WHO Expert Committee on the Control of Schistosomiasis called for greater flexibility and a more prominent role for Primary Health Care services (PHC) and other sectors in sustainable implementation (WHO, 1993), most of the schistosomiasis control activities in sub-Saharan Africa have been stopped since.