There are two major epidemiologic forms of E. granulosus–induced echinococcosis, pas-toral and sylvatic. The more common pastoral form has its highest incidence in Australia, New Zealand, South and East Africa, the Middle East, Central Europe, and South Amer-ica, where domestic herbivores such as sheep, cattle, and camels are raised in close con-tact with dogs. Although approximately 200 human cases are reported each year in the United States, most were acquired elsewhere. Indigenous cases do occur, however, partic-ularly among Basque sheep farmers in California, southwestern Native Americans, and some Utah shepherds. Animal husbandry practices that permit dogs to feed on the raw viscera of slaughtered sheep allow the cycle of transmission to continue. Shepherds become infected while handling or fondling their dogs. Eggs retained in the fur of these animals are picked up on the hands and later ingested. Sylvatic echinococcosis is found principally in Alaska and western Canada, where wolves act as the definitive host and moose or caribou as the intermediate. In two counties in California, a second cycle in-volving deer and coyotes has been described. When hunters kill these wild deer and feed their offal to accompanying dogs, a pastoral cycle may be established.
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