Which organism is responsible for causing schistosomiasis?

Schistosomiasis is caused by parasitic worms belonging to the genus Schistosoma, with Schistosoma mansoni being one of the primary species responsible for this disease. These worms are helminths, specifically trematodes, which infect humans through contact with contaminated freshwater sources where the larvae are present.

Upon entering the human body, the mature worms reside in the blood vessels, especially around the intestines or bladder, depending on the species. The disease is characterized by a range of symptoms, including abdominal pain, diarrhea, and, in severe cases, organ damage due to the inflammatory response triggered by the eggs laid by the female worms.

Other organisms listed are responsible for different diseases: Plasmodium vivax is implicated in malaria, Toxocara canis is a roundworm that causes toxocariasis, and Giardia intestinalis leads to giardiasis. Each of these pathogens has its own life cycle, reservoir, and transmission route distinct from Schistosoma mansoni, which specifically highlights why the first choice is correct for schistosomiasis.