What finding provides the best direct diagnosis of Echinococcus granulosus infection in humans?

• A. Hydatid cysts in tissues
• B. Adult worms in the intestine
• C. Adult worms in tissues
• D. Eggs in feces

Answer: (A)

In human echinococcosis, the finding that directly proves infection is the presence of hydatid cysts in tissues. These cysts are the larval stages of Echinococcus granulosus and form primarily in the liver and lungs after eggs are ingested by humans. The cysts contain fluid and protoscoleces, which provide concrete evidence that the parasite has established an infection in human tissue.

Other scenarios don’t offer direct proof in humans: adult tapeworms live in the intestines of the definitive hosts (like dogs), not in people, so finding adult worms in human tissue isn’t possible. Eggs in feces come from the definitive host and, in humans, wouldn’t be a direct indicator of infection; eggs are also indistinguishable from those of related tapeworms and don’t demonstrate human tissue infection. Therefore, hydatid cysts in tissues best confirm the diagnosis.