Which parasite causes hydatid disease in humans leading to cyst formation in organs?

• A. Taenia solium
• B. Giardia lamblia
• C. Entamoeba histolytica
• D. Echinococcus granulosus

Answer: (D)

Hydatid disease comes from infection with Echinococcus granulosus, a small dog tapeworm. Humans ingest the eggs shed in dog feces, the larvae travel to organs such as the liver and lungs, and develop into large cysts called hydatid cysts. These cysts often contain daughter cysts and can grow quite large, causing space-occupying effects and potential rupture, which can lead to severe reactions. This organ-cyst pattern is characteristic of Echinococcus granulosus infection.

The other parasites listed cause different diseases. Taenia solium leads to cysticercosis and taeniasis, not hydatid cysts. Giardia lamblia causes giardiasis, a gastrointestinal infection. Entamoeba histolytica causes amebic dysentery and can form liver abscesses, but not classic hydatid cysts.