Question
Hydatid disease
Answer
Hydatid disease (echinococcosis) is a zoonotic infection caused by the larval (cystic) stage of Echinococcus granulosus (dogs are the definitive host; sheep/cattle are the usual intermediate host; humans are an accidental intermediate host).
Transmission: humans acquire infection by ingesting eggs shed in dog faeces; ingested eggs hatch, releasing oncospheres that disseminate via the bloodstream, most commonly lodging in the liver and lungs, developing slowly into a fluid-filled hydatid cyst.
Cyst structure: outer host-derived pericyst; laminated (acellular) membrane; innermost germinal layer producing brood capsules with numerous protoscolices (“hydatid sand”), and sometimes daughter cysts.
Clinical features: often asymptomatic for years; symptoms from mass effect on the affected organ; cyst rupture can cause severe anaphylactic reaction and secondary dissemination.
Diagnosis: imaging (ultrasound/CT/MRI) is the primary tool; serology (ELISA) supports diagnosis.
Treatment: surgical excision (avoiding spillage) with perioperative albendazole; PAIR technique for selected cysts.
Prevention: deworming of dogs, avoiding feeding dogs raw offal, hand hygiene.