A traveller from Bihar develops hepatic cysts on ultrasound. Indirect haemagglutination (IHA) titres are 1:512. ELISA is positive for Casoni antigen. Which helminth is most likely responsible, and what is the infective stage for humans?
- A Echinococcus granulosus — infective stage is the oncosphere (hexacanth embryo) in eggs ✓
- B Taenia solium — infective stage is the cysticercus in undercooked pork
- C Fasciola hepatica — infective stage is metacercaria on aquatic vegetation
- D Clonorchis sinensis — infective stage is metacercaria in freshwater fish
Explanation
Hydatid disease is caused by Echinococcus granulosus. Humans are accidental intermediate hosts who ingest eggs from dog faeces; the hexacanth embryo (oncosphere) hatches in the duodenum, penetrates the gut wall and lodges in the liver forming a hydatid cyst. The IHA (Casoni) serology titres >1:256 are highly suggestive. Taenia solium cysticercosis can also cause tissue cysts but favours brain and muscle; the infective stage in that case is also the egg (for cysticercosis) or cysticercus (for intestinal taeniasis). Fasciola and Clonorchis cause biliary/hepatic disease but via metacercariae in water plants and fish respectively.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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