Digenetic trematodes have evolved behavioral adaptations to their complex life cycles. They have their own strategies to fi nd hosts, locate sites of infection within fi nal and intermediate hosts, escape
immune responses, etc. Many of these strategies are highly complex, but they are sometimes quite subtle. While the mechanisms or processes involved in a few parasites are understood, most are not. Schistosoma mansoni parasites inhabit three distinct environments: water, intermediate molluscan hosts, and a defi nitive vertebrate host. Although targeted chemotherapy and other public health measures are employed to control schistosomiasis and its spread, there is a need for the development of vaccine and new anti-schistosome drugs. Determining how schistosomes interact with different environments may be one mechanism by which suitable vaccine or chemotherapeutic
drugs could be developed. Genes expressed in a stage-specifi c manner may help us to understand the molecular events controlling the complex life cycle of schistosomes. Various proteins are expressed during the life cycle of schistosomes which are essential for its miracidial infection of molluscan hosts, cercarial penetration of vertebrate skin, evasion of the immune responses of both hosts, and other biological activities needed by schistosomes to complete their complex life cycle. Identifying these stage-specifi c proteins may uncover hidden aspects of parasite biology and provide useful leads for the development of novel intervention strategies.

Keywords: Helminth Proteins - antagonists & inhibitors, Helminth Proteins - metabolism, Humans - parasitology, Schistosoma mansoni - growth & development, Schistosoma mansoni - physiology, Schistosomicides - chemistry, Helminth Proteins - metabolism, Host-Parasite Interactions, Humans - parasitology, Life Cycle Stages, Models, Biological, Reverse Transcriptase Polymerase Chain Reaction, Schistosoma mansoni - physiology, Schistosomicides - therapeutic use