ABSTRACT
Schistosomiasis is an ancient neglected disease with effects worldwide, particularly in the tropics and subtropics. It ranks second to malaria, with currently over 240 million people infected worldwide. Human infections are caused by the blood flukes genus Schistosoma, primarily, S. mansoni, S. japonicum, and S. haematobium. The vector is freshwater snails (Biomphalaria spp.). An infected person excretes eggs, which hatch in water and release larvae called miracidia. Miracidia infect freshwater snails, which multiply and produce thousands of infectious larval stages called cercariae. Cercariae emerge from the snail into surrounding water. Humans become infected by skin contact with contaminated water. Man-made reservoirs and poorly designed irrigation schemes are the major grounds for schistosomiasis evolvement.
Currently, praziquantel and oxamniquine are the treatment regimens for schistosomiasis. Human vaccines are in the developmental stages. The other control measures are health education and improved sanitation. Nevertheless, control of the snail vector plays a major role in the successful control of schistosomiasis. Since molluscicidal efforts using synthetic compounds are very expensive with various adverse effects, there is a growing interest in biological methods as alternates. This chapter discusses in detail the various biological methods for the control of Schistosoma transmission through aquatic snails. They are application of (a) bacterial pathogen such as Candidatus Paenibacillus glabratella and Bacillus thuringiensis (thuricide); (b) plant-derived saponin molluscicides such as Phytolacca dodecandra (endod), Tetrapleura tetraptera, Balanites aegyptiaca, Agave sisalana, Ambrosia maritima, Swartzia madagascariensis, Sesbania sesban, Furcraea selloa marginata, and Anacardium occidentale; (c) predators such as Sciomyzidae (marsh flies), Ostracoda (Crustacea) Macrobrachium vollenhovenii (prawn), Trematocranus placodon, Astatoreochromis alluaudi and Sargochromis codringtonii (fish), and Procambarus clarkii (crayfish); (d) competitor snails like Marisa cornuarietis (ampullarid), Melanoides tuberculata (thiarid), Planorbella duryi, Helisoma trivolvis (mollusk), and Pomacea maculate (apple snail); and (e) genetic manipulation of snails. A review of the aforementioned methods, their advantages and disadvantages, their field application, practical difficulties, and evaluation effects are included in the chapter.
