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Echinococcosis, also referred to as hydatid disease, is a general term used to define zoonosis caused by Echinococcus tapeworms, or cestodes. There are four types of Echinococci, the most common seen worldwide is Echinococcus granulosis whose adult form parasite the dog’s small intestine and the larval form that develops in humans, and alveolar echinococcosis, caused by Echinococcus multilocularis and restricted to the northern hemisphere (12). Echinococcosis of the central nervous system is the most common brain parasitic infection in the world. It is a cosmopolitan anthropozoonosis and represents a significant public health problem. Humans are the accidental intermediate host in the life cycle of this genus. Intracranial pressure, seizure and focal deficit are common signs. CT scan and MRI are the choice exams. Surgery is the radical treatment. Echinococcus granulosus has a two host life cycle with canids as the definitive host for adult worms and ungulates as the intermediate host for the larval worms. The adult worms are small, about 3-5 mm in length, and live in the small intestine of canids (dogs, wolves, foxes, dingo, and jackals). The adult worms lay eggs that are passed in the feces of the canid and are accidently ingested by ungulates (deer, elk, moose, caribou, domestic sheep, domestic cattle, etc) where the eggs hatch in the rumen and migrate to the thoracic or abdominal cavity and form sac like structures called hydatid cysts. Within the hydatid cysts, hundreds of immature tapeworms bud off the lining of the cyst. If a canid consumes a hydatid cyst, the larval tapeworms develop into adult worms in the small intestine of the canid. Echinococcus granulosus has a worldwide distribution (Gottstein 1992). There are two recognized biotypes of the parasite – the northern or sylvatic biotype that circulates between canids (wolf, dog) and cervids (moose, caribou, reindeer, deer and elk) and is present above 45° latitude. The northern biotype does not appear to cross-infect domestic livestock (Rausch 1986). The domestic biotype, comprised of at least nine different strains, circulates between dogs and domestic ungulates, especially sheep or other endemic species of wildlife (lions and sheep, dingoes and dogs and macropod marsupials, etc) (Jones and Pybus 2001). It is endemic in most sheep raising areas of the world including the southwestern United States, central and South America, the Middle East, northern Africa, and Australia (Loveless et al. 1978; Jones and Pybus 2001). Echinococcus multilocularis has a two host life cycle with canids as the definitive host for adult worms and rodents as the intermediate host for the larval worms. The adults are small and live in the small intestine of dogs, foxes and cats. The eggs are passed in the feces and accidently ingested by small rodents, primarily mice and voles, in which the eggs hatch and migrate to the abdominal cavity and form multicompartmental hydatid cysts called alveolar or multilocular cysts. If a canid consumes a multilocular cyst, the larval tapeworms develop into the adult worms in the small intestine of the canid. Echinicoccus multilocularis has a worldwide distribution in the northern hemisphere (Gottstein 1992) and is endemic in south central Canada and the northern Midwestern states in the United States (Leiby et al. 1970). The parasite in Idaho
