The slender rhabditiform larvae of which of the following helminths move about in water and are ingested by species of cyclops –
**Core Concept**
The question is testing the student's knowledge of the life cycle of a specific helminth parasite, specifically the intermediate host and its relationship with the larval form. The slender rhabditiform larvae of a particular parasite are ingested by species of cyclops, a type of small crustacean that serves as an intermediate host.
**Why the Correct Answer is Right**
The correct answer, D. medinensis, is the causative agent of dracunculiasis, also known as Guinea worm disease. The life cycle of D. medinensis involves the ingestion of contaminated water containing the slender rhabditiform larvae by a species of cyclops. The larvae then develop into a procercoid stage within the cyclops, which is subsequently ingested by a human host. This infection leads to the migration of the larvae through the human body, eventually causing the characteristic blister and skin lesions associated with the disease. The cyclops serve as an essential intermediate host in the life cycle of D. medinensis.
**Why Each Wrong Option is Incorrect**
**Option A:** D. latum, also known as the fish or broad tapeworm, does not have a life cycle that involves cyclops as an intermediate host. Instead, it is typically ingested by humans through the consumption of undercooked or raw fish infected with the parasite.
**Option C:** W.bancrofti, the causative agent of lymphatic filariasis, has a life cycle that involves mosquitoes as the vector and intermediate host, not cyclops.
**Option D:** S. mansoni, the causative agent of schistosomiasis, has a life cycle that involves freshwater snails as the intermediate host, not cyclops.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that dracunculiasis, caused by D. medinensis, is a waterborne disease that can be prevented through proper water treatment and hygiene practices. The use of contaminated water for drinking, cooking, or washing is a significant risk factor for infection.
**✓ Correct Answer: B. D. medinensis**