Echinococcosis is an infection caused by tapeworms. This kind of worm is often found in dogs, sheep, and cows. They live in the animal's belly. The eggs are shed into the animal's stool. You may become infected when you take the eggs into your mouth. The egg can settle in your organs like your brain, liver, and lungs. They grow into cysts over time. These cysts can cause problems with many parts of your body.