What form of transmission is primarily responsible for the spread of Echinococcus granulosus?

Echinococcus granulosus, the causative agent of hydatid disease, is primarily transmitted through the ingestion of eggs shed in the feces of infected definitive hosts, which are typically canines such as dogs. When humans accidentally ingest these eggs, often through contaminated food, water, or hands, they can develop cysts in various organs, particularly the liver and lungs. This mode of transmission highlights the importance of proper hygiene and sanitation practices, especially in areas where dogs may have access to contaminated food sources or where livestock are present.

The other modes of transmission listed do not accurately reflect the lifecycle of Echinococcus granulosus. Inhalation of spores does not apply, as this parasite does not produce spores. Direct contact with infected animals may occur in environments where dogs are kept, but it is not the primary method of transmission; instead, it is the eggs in the feces that pose a risk. Blood transfusion is not a recognized mode of transmission for this parasitic infection, as Echinococcus granulosus is not transmitted through blood.