Schistosoma mansoni is a parasitic flatworm that causes a disease known as schistosomiasis, primarily affecting humans in tropical and subtropical regions. The parasite lives in freshwater snails, which release larvae into the water. When humans come into contact with contaminated water, the larvae can penetrate the skin and enter the bloodstream. Once inside the body, S. mansoni matures into adult worms, which reside in the blood vessels of the intestines. The infection can lead to various health issues, including abdominal pain, diarrhea, and liver damage. Preventive measures include improving sanitation and avoiding contact with contaminated water sources.