Three weeks after rafting in a lake endemic for schistosomiasis, a previously healthy traveller develops fever, urticaria, cough, myalgia, marked peripheral eosinophilia, and tender hepatosplenomegaly. Blood films are negative for malaria parasites. The pathogenesis of this acute illness is best explained by:

• A Type III hypersensitivity due to circulating immune complexes of schistosomal antigens and antibodies ✓
• B Type I hypersensitivity to helminth cuticle antigens
• C Direct cytopathic effect of cercarial penetration on hepatocytes
• D Granulomatous reaction around deposited eggs in liver parenchyma

Explanation

Katayama fever represents acute schistosomiasis occurring at the onset of oviposition. It results from type III hypersensitivity, with circulating immune complexes of adult worm and egg antigens bound by antibody depositing in tissues, producing fever, rash, arthralgia and eosinophilia. Granulomas around deposited eggs drive chronic intestinal and hepatic disease, not this acute systemic syndrome, and cercariae do not invade hepatocytes directly.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.