Dracunculus intermediate host — DTM&H MCQ
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Correct answer: C — Cyclops copepod
The correct answer is C, Cyclops copepod. Dracunculus medinensis (guinea worm) larvae are ingested by tiny freshwater crustaceans of the genus Cyclops, which act as the obligate intermediate host; humans become infected by drinking unfiltered pond or stagnant water containing these infected copepods. After roughly a year, the gravid adult female migrates to the skin, typically the lower leg, and emerges to release larvae when the affected limb is immersed in water, completing the cycle. This history of a slow-emerging leg worm after drinking untreated pond water in an endemic area such as Chad is the classic dracunculiasis presentation, and the copepod vector is the discriminating feature examiners test. Why the other options are wrong: B. Biomphalaria snail: this is the intermediate host for Schistosoma mansoni, not Dracunculus; schistosomiasis presents with haematuria, bladder or liver disease rather than a slowly emerging limb worm. D. Anopheles mosquito: transmits malaria (Plasmodium species) and some filarial infections such as Wuchereria bancrofti, but plays no role in dracunculiasis, which is waterborne, not vector-bitten. E. Triatomine bug: the vector for Trypanosoma cruzi (Chagas disease) in the Americas, transmitted by contamination of bite wounds with infected faeces, unrelated to guinea worm biology. A. Freshwater crab: acts as intermediate host for Paragonimus (lung fluke) after ingestion of undercooked crab meat, not for waterborne Dracunculus infection. Key point: a year-long incubation followed by a worm emerging from the leg after drinking unfiltered water points to Dracunculus medinensis transmitted via Cyclops copepods, not an insect or mollusc vector.
Reference: World Health Organization, Dracunculiasis (Guinea-worm disease) fact sheet: dracunculiasis is transmitted when people swallow water contaminated with parasite-infected water-fleas (Cyclops), https://www.who.int/news-room/fact-sheets/detail/dracunculiasis-(guinea-worm-disease)