Paragonimus westermani (lung fluke) infection is acquired by eating raw or undercooked crabs or crayfish. Which intermediate hosts are involved in the life cycle and what is the infective stage for humans?

• A First host: freshwater crab; Second host: snail; Infective stage: cercariae
• B Only one intermediate host (freshwater snail); Infective stage: miracidium
• C First host: copepod; Second host: fish; Infective stage: plerocercoid
• D First host: snail (Melania sp.); Second host: freshwater crab/crayfish; Infective stage: metacercaria ✓

Explanation

P. westermani uses two intermediate hosts: the first is a freshwater snail (Melania/Semisulcospira sp.) where miracidia develop through sporocyst-redia-cercaria stages; the second is freshwater crabs or crayfish where cercariae encyst as metacercariae. Humans are infected by ingesting metacercariae in raw shellfish. Metacercariae excyst in the duodenum, penetrate the gut wall, and migrate to the lungs. The plerocercoid is the larval stage of Diphyllobothrium latum in fish.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.