Scoleces (Hydatid Sand)

This photographs shows a number of scoleces of Echinococcus. During their life cycle within the host, these tapeworms pass through an egg stage which are hatched in the duodenum releasing an embryo (oncosphere). The oncosphere penetrates through the intestinal wall and is carried via circulatory system to various sites such as liver and lung. The next stage (larval stage) is characterized by the formation of a thick-walled cyst which is lined by germinal epithelium. The cyst undergoes enlargement producing daughter cysts and protoscolices. The protoscolices may be attached to the cyst wall or float freely in the milky fluid contents giving it a sandy consistency (Hydatid sand). The cysts may rupture into the tissue releasing the protoscolices causing further dissemination. Image courtesy of: CDC/ Dr. Mae Melvin