Ingested eggs hatch and release embryos (onchospheres) into the small intestine of the host. These embryos penetrate the intestinal mucosa, enter the blood circulation of the host and
are carried to the liver and other sites where cystic development (metacestode) starts (Figure 18.1). Spherical well-delineated, primary cysts, containing living scolices, are formed in the human host. These cysts are most often found in the liver (65% of cases) followed by the lungs (25%) and other organs such as kidney, spleen, reproductive organs, heart, and seldom in bone. The space-occupying process causes repression or displacement of vital host tissue, vessels or organs. Thus, the clinical manifestations of the disease are determined by the site, the size and the number of cysts (Gottstein and Hemphill 1997).
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