Schistosoma japonicum resides in –
**Core Concept**
Schistosoma japonicum is a parasitic flatworm that causes schistosomiasis, a tropical disease prevalent in Asia. The parasite's lifecycle involves two main hosts: a definitive host (primates, including humans) and an intermediate host (freshwater snails).
**Why the Correct Answer is Right**
Schistosoma japonicum resides in the mesenteric veins of the small intestine, where it lays eggs that can cause granulomatous inflammation and fibrosis. The parasite's eggs are excreted in the feces and contaminate freshwater sources, allowing the snail intermediate host to become infected. The cercariae, freed from the snail, infect humans through skin contact with contaminated water.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Schistosoma mansoni resides in the superior mesenteric veins of the large intestine, not Schistosoma japonicum.
**Option B:** This option is incorrect because Schistosoma haematobium resides in the vesical plexus and the bladder, not Schistosoma japonicum.
**Option C:** This option is incorrect because while Schistosoma japonicum does affect other organs, it primarily resides in the mesenteric veins of the small intestine.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the choice of antischistosomal treatment depends on the species of Schistosoma, with praziquantel being the first-line treatment for S. japonicum, S. mansoni, and S. haematobium.
**Correct Answer: C. Mesenteric veins of the small intestine.**