Echinococcus:
Metazoa Platyhelminthes Cestoidea Cyclophyllidea Taeniidae Echinococcus

These parasitic worms typically infect cattle. If you eat meat that is contaminated with their eggs, those eggs will hatch in your small intestine, and then, as larvae, migrate through your circulatory system to other parts of your body. The larvae will eventually develop into a spherical cyst filled with fluid and protoscolices, which grow into adult worms. The parasite is spread when these cysts are ruptured.

Echinococcus cysts often grow to a diameter of 16 centimeters, although they may become as large as a basketball. The seriousness of the infection is dependent upon the size and location of the cyst: a large cyst in the liver may be fatal, as well as a small cyst in the brain. Symptoms of an infection are not usually apparent until the cyst grows to approximately 10 centimeters.