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Epidemiology and Pathology

To complete its life cycle, E. granulosus requires two hosts: a canine and a grazing animal (Figs. 3.2 & 3.3). In the more common pastoral form, the primary host is the dog, while herbivores such as sheep, cattle, swine, or camels serve as intermediate hosts. In the less common sylvatic form, the wolf or fox is the primary host and reindeer or moose are the usual intermediate hosts. Humans are accidental intermediate hosts. There is a high degree of host specificity in the primary, but not in the intermediate host; the domestic cat, for instance, is not a primary host. The reasons for this unexplained specificity may include the microtopography of the host's intestine, biochemical and immunological factors, or the composition of the host's bile.

Fig. 3.2. Life cycles of the various forms of hydatid disease: E. multilocularis and E. granulosus (sylvatic and pastoral). The common hosts are represented.

Fig. 3.3 Detailed life cycle of Echinococcus granulosus. AFIP 68-3573-15 (Phyllis Smith).

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