Echinococcus granulosus (Echinococcosis)

Biology
The definitive hosts are carnivorous predators including dogs, wolves, foxes, and lions. The adult tapeworm lives in the small intestine of the definitive host and produces embryonated eggs which are excreted in the stool. The intermediate hosts are infected by ingesting the eggs, and include any mammals, most commonly sheep, goats, cattle, camels, pigs, wild herbivores, and rodents.

In the intermediate host, the eggs hatch to form an oncosphere which penetrates the intestinal wall and is carried by the bloodstream to the liver, lungs, brain, and other organs. It settles there and turns into a thick-walled hydatid cyst. Protoscoleces bud from its wall and protrude into the fluid that fills the cyst.

After the intermediate host dies, a definitive host eats the flesh of the intermediate host. Protoscoleces turn inside out, attach to their intestines, and turn into adult tapeworms.

Humans can ingest the embryonated eggs and become infected with the oncospheres that form hydatid cysts in a variety of organs. If the cysts rupture the protoscolices may create secondary cysts in other parts of the body, called secondary echinococcosis.

Risk factors

 * Drinking water contaminated by dog feces
 * Direct contact with dogs

Epidemiology
Echinococcosis is endemic the Middle East, Mediterranean, Australia, New Zealand, South American, and central and south Europe.

Treatment
CNS echinococcosis is treated with surgical removal of the cyst. Importantly, it must be removed whole, as it contains highly antigenic contents that can cause anaphylaxis when released.