**1. Introduction**

358 Current Topics in Tropical Medicine

Steinmann, P.; Keiser, J.; Bos, R.; Tanner, M. & Utzinger, J. (2006). Schistosomiasis and water

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*Schistosoma mansoni* harboured in mice treated with artemether. *Acta Tropica*,

M.; Hassan, I.; Mahmoud, K.; El-Hallouty, S.M.; El-Gendy, M.; Gohar, L.; El-Manawaty, M.; Fayyad, W. & El-Menshawi, B.S. (2007). Large-scale *in vitro* screening of Egyptian native and cultivated plants for schistosomicidal activity. 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

Control of Schistosomiasis and Soil-Transmitted

children in sub-Saharan Africa.

Helminthiasis in Sub-Saharan Africa: Challenges and Prospects 361

The epidemiology of helminth infections is influenced by several key determinants, including environment, population heterogeneity, age, household clustering, genetics and polyparasitism (Hotez et al., 2008). In recent years, considerable progress has been made in the use of geographical information system (GIS) and remote sensing (RS) to better understand helminth ecology and epidemiology, and to develop low-cost ways to identify target populations for treatment. GIS and RS were used to describe the global distribution of schistosomiasis and STH infections and to estimate the number of infections in school-age

There is considerable geographical variation in the occurrence of infections (Brooker et al., 2009). In general, changes with age in the average intensity of helminth infections tend to be convex, rising in childhood and declining in adulthood. For schistosomiasis, *A. lumbicoides* and *T. trichiura*, the heaviest and most frequent infections are in children aged 5–15 years, with a decline in intensity and frequency in adulthood (Gilles, 1996). In contrast, hookworm frequently exhibits a steady rise of intensity of infection with age, peaking in adulthood (Bethony et al., 2002). Household clustering of infected individuals has been demonstrated for STH (Forrester et al., 1988), and this can persist through time, as shown by familial predisposition to heavy infection with *A. lumbricoides* and *T. trichiura* (Forrester et al., 1990). Because morbidity is associated with worm burden rather than the absence or presence of infection, prevalence is commonly combined with worm burden (intensity of infection) to assess the epidemiological situation for schistosomiasis and STH infections. Worm burden is commonly measured by the number of eggs per gram (EPG) of feces or eggs per 10ml of urine (Anderson, 1982; Montresor et al., 1998). Prevalence and intensity of infections are used to classify communities into transmission categories, which enable to determine the appropriate type of mass treatment a community should receive (WHO, 2006). Both should

Progress in implementing schistosomiasis and STH control programmes has been slow but steady. Since 2006, there has been an overall increase in the number of people treated for schistosomiasis and STH. The increase in treatments has occurred entirely in the African Region, where the number of people treated more than doubled from 2006 to 2009 (WHO, 2011). This number increased by 93% in 2010. The increase in the number treated suggests that both governments and their donor partners are now investing in schistosomiasis control (WHO, 2012). In 2010, 18 over 42 schistosomiasis endemic countries in the African region and 34/46 STH endemic countries or territories reported their treatment data to WHO. Overall, 27,983,327 people were treated for schistosomiasis, and 91,025,863 children for STH (Table 1).

Characteristics Schistosomiasis STH No. endemic countries 42 46 No. countries reporting MDA data 18 34 No. people requiring treatment 220 578 484 283 800 000 No. people treated 27 983 327 91 025 863 No. pre-school aged children treated - 42 711 551 No. school aged children treated - 48 314 312 Table 1. African Regional summary of children treated for schistosomiasis and STH, 2010

be assessed in monitoring the impact of deworming campaigns.

**3. Control of schistosomiasis and STH 3.1 Progress towards the 2010 global target** 

countries, the most affected part of the world. In the 1990s, interest in the control of these diseases in Africa waned. Therefore, as with other neglected tropical diseases (NTDs), schistosomiasis and STH control has been overshadowed by other health priorities. The highest priority of the international health community was given to the 'big three', i.e. HIV/AIDS, tuberculosis and malaria, with less attention to other infections related to poverty (Molyneux et al., 2005).

Recent years have witnessed an increased interest in the control of NTDs, and today there exists a global momentum for the control of these diseases. The control of NTDs has become a priority on the agenda of many governments, donors and international agencies. The World Health Organization (WHO) has played a major role in this prospect. Indeed, under the aegis of WHO, all member states of WHO (over 200 countries) have endorsed in May 2001 the World Health Assembly resolution WHA 54.19, with as a major objective the regular treatment of at least 75% of all school-aged children at risk of morbidity by 2010. The renewed impetus for schistosomiasis and STH control has generated a greater political commitment, as well as an unprecedented opportunity for cost-effective action (Molyneux et al., 2005). This momentum has encouraged many countries to establish national action plans and programmes to control schistosomiasis, STHs and other NTDs (Hotez et al., 2009; Tchuem Tchuenté & N'Goran, 2009). Within the past decade, significant progress has been made on large scale treatments through integrated control of schistosomiasis, STH and other NTDs, thanks to a number of international organizations, donor foundations, bilateral institutions and non-governmental organizations that responded to the 2001 WHO's call for action (Savioli et al., 2009). Today, treatment is cost-effective and the 'preventive chemotherapy' is currently the strategy of choice (WHO, 2006). With a support from the American (USAID) and British (DFID) governments, as well as the Bill and Melinda Gates Foundation, the pharmaceutical industry, and many not-for profit organizations, millions of children are regularly treated for schistosomiasis, STH and other NTDs. However, the control of these diseases is a long-term undertaking which involves several challenges. This paper highlights the progress made and also focuses on some main challenges that are reviewed and discussed.
