A farm worker presents with cough, wheeze, and blood-tinged sputum accompanied by marked eosinophilia and fleeting pulmonary infiltrates on chest radiograph. Sputum examination shows motile larvae. Which developmental stage of Ascaris lumbricoides traverses the pulmonary capillaries into the alveoli to produce this picture?

• A Embryonated egg containing second-stage larva
• B Rhabditiform larva hatching in the small intestine
• C Third-stage filariform larva carried in venous blood ✓
• D Gravid adult female worm migrating retrograde

Explanation

Ingested embryonated eggs hatch in the jejunum, releasing second-stage rhabditiform larvae that penetrate the intestinal wall and enter the portal circulation. They molt to become third-stage filariform larvae in the liver and reach the pulmonary capillaries, where they break into the alveoli causing Loeffler syndrome before ascending to be swallowed again. Rhabditiform larvae of Ascaris do not migrate systemically, and adults never leave the gut lumen.

Reference: Paniker's Textbook of Medical Parasitology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.