In Echinococcus granulosus infection, hydatid cysts are most often located in which organs?

• A. Brain
• B. Spleen
• C. Liver and lung
• D. Kidney

Answer: (C)

When Echinococcus granulosus infection causes hydatid disease, the larvae reach the body through the bloodstream after crossing the intestinal wall. The liver serves as the first capillary filter for portal blood from the gut, so most larvae get trapped there and form cysts in the liver. If some larvae bypass or escape this first filter, they travel to the lungs, which act as the next capillary filter, and many cysts develop in the lung tissue. This filtration sequence—liver first, then lungs—explains why these two organs are the most commonly involved. Involvement of the brain, spleen, or kidney is much less frequent and occurs only in rare cases of spread.