Epidemiologic investigation of echinococcosis in American Indians living in Arizona and New Mexico.

Ten cases of echinococcosis diagnosed in American Indians in Arizona and New Mexico between 1972 and 1975 were investigated as part of a regional epidemiologic study. Patients were visited at home to discover factors associated with local parasite transmission, to detect possible additional cases among family members, and to perform diagnostic tests on dogs. Six patients were Navajo, 2 Zuni, and 2 Santo Domingo Indians. An additional case in a Navajo man was detected by serologic testing of patients' family members; this was the 20th case diagnosed in the region since 1965. Dogs owned by three of the Navajo patients were infected with Echinococcus granulosus. Arecoline-purge testing of 110 dogs in the Zuni pueblo demonstrated echinococcosis in a single stray dog. The findings at slaughter of Navajo-owned sheep indicate that the infection is enzootic in this intermediate host. The epidemiologic findings suggest that humans were infected from dogs which contracted their infections from two sources. The first was sheep raised locally in rural areas of the Navajo Reservation where the infection is enzootic in the dog-sheep cycle; transmission was apparently facilitated by the widespread practice of home butchering. A second source of human infection was dogs which became infected by eating viscera of sheep of off-reservation origin; these sheep were purchased and butchered by individual families in urban areas of the Navajo Reservation and in the Zuni and Santo Domingo pueblos.