**1.2 Schistosomiasis—the disease burden and current chemotherapy**

Schistosomiasis, widely known as bilharzia, is caused by infection with blood flukes of the genus *Schistosoma* which is transmitted through contact with infected fresh-water snail vectors. Schistosomiasis is reported to be the 2nd leading endemic parasitic disease in the world after malaria. The disease affects more than 240 million people in tropical and subtropical areas with about 90% cases reported from sub Saharan Africa [23, 24].

Five species of the schistosome parasite namely: *Schistosoma mansoni*, *Schistosoma haematobium*, *Schisosoma japonicum*, *Schistosoma mekongi*, and *Schistosoma intercalatum* usually affect humans [25]. In sub-Saharan Africa the main burden of disease is usually attributed to *S. mansoni* and *S. haematobium* which cause intestinal and urinary schistosomiasis respectively [10]. The infection is mainly characterized by painful bloody urination in urinary schistosomiasis or blood stained diarrhea in intestinal schistosomiasis. Long term effects include liver fibrosis, renal failure, cancer of the bladder, infertility and increased risk of contracting HIV. In children, schistosomiasis results in malnutrition, growth retardation, cognitive defects and chronic anemia [6, 26].

For the eradication of schistosomiasis, control programmes have been based on preventive chemotherapy. The WHO endorsed and advocated for mass drug administration (MDA) especially among school children utilizing a single oral dose of 40 mg/kg praziquantel [27]. Unfortunately, the unavailability of the drugs due to cost, poor drug coverage, inequity of access to chemotherapy and noncompliance to therapy due to adverse side effects have impeded the progress of this approach [7, 28]. The expansion of preventive chemotherapy has also raised concerns about the potential development of resistance to praziquantel (PZQ ) which remains the only commercially readily available drug for the control of schistosomiasis [29]. Some studies have reported low cure rates of PZQ attributing this to possible mutation of the schistosome parasite as well as inactivity of PZQ against early stages of the worms [30, 31]. It is thus not a satisfactory situation to have only one single effective treatment. Ideally, other anti-schistosome drugs should be developed so that the classical strategy of avoiding development of resistance could be followed.
