Control of Schistosomiasis and Soil-Transmitted Helminthiasis in Sub-Saharan Africa: Challenges and Prospects

Abstract

Schistosomiasis and soil-transmitted helminthiasis (STH) are the most common types of parasitic infections in the world. These diseases have major health and socio-economic repercussions, and constitute an important public health problem in developing countries. Human schistosomiasis is caused by six species of schistosomes, i.e. Schistosoma haematobium, Schistosoma mansoni, Schistosoma japonicum, Schistosoma mekongi, Schistosoma intercalatum and Schistosoma guineensis; and is endemic in 78 countries, where 779 million people are at risk of infection. S. haematobium is responsible for urogenital schistosomiasis, and the other species cause intestinal schistosomiasis. It is estimated that 207 million people are infected (WHO, 2002; Steinmann et al. 2006). STH, also known as intestinal worm infection, is caused by four main species of worms commonly known as roundworms (Ascaris lumbricoides), whipworms (Trichuris trichiura) and hookworms (Ancylostoma duodenale and Necator americanus). It is estimated that STH affects more than 2 billion people worldwide, and the greatest numbers of infections occur in sub-Saharan Africa, the Americas, China and east Asia (WHO, 2006; Hotez et al., 2006; Brooker et al., 2006; Awasthi et al., 2003). These diseases affect the poorest of the poor and infections are particularly abundant among people living in rural or deprived urban settings with low socio-economic status, lack of clean water and poor sanitation (Hotez et al., 2006). The morbidity caused by these worms is commonly associated with heavy infection intensities. Compared with any other age group, school-aged children and pre-school children are the most vulnerable group and they harbor the greatest numbers of intestinal worms. As a result, they experience growth stunting and diminished physical fitness as well as impaired memory and cognition (Crompton and Nesheim, 2002; Stephenson et al., 2000; Bethony et al., 2006). These adverse health consequences combine to impair childhood educational performance and reduce school attendance (Miguel & Kremer, 2004; Hotez et al., 2008). Studies have demonstrated that children may acquire helminth infections early in life (Sousa-Figueiredo et al., 2008; Stothard et al., 2008); which causes initial organ damage that can remain subclinical for years and manifest overtly only later, in adulthood (WHO, 2006; Odogwu et al., 2006). Despite the existence of tools in the 1970s and 1980s, control was sustained for a prolonged period only in few countries and almost no progress was made in sub-Saharan African