host. It can, however, pass through an intermediate host, as well. The most common intermediate hosts for H. nana are arthropods (e.g. flour beetles). When an egg is ingested by the definitive host, it hatches and releases a six-hook larva called the oncosphere (hexacanth) which penetrates the villi of the small intestine and develops into a cysticercoid. Infection Transmission of H.nana occurs by the fecal-oral route. It also occurs by accidental ingestion of an insect containing the cysticercoid. Screening for activity against H. nana H. nana in mice is used because: Human infection is easily maintained in mice. Its armed scolex is similar to other pathogenic tapeworms. It corresponds to other tapeworms in its sensitivity to standard anthelmintics, Method: Mature worms are collected from infected mice. Terminal gravid proglottids are removed, crushed under coverslips, and eggs are removed. Eggs containing hooklets (mature) are counted. 0.2 ml stock soln. containing 1000 eggs/ml given to each mouse. Adult worms develop in 15–17 days. The test drug is given orally; mice are necropsied on the third day after treatment. A standard drug is given. The intestines are examined under a dissecting microscope for worms or scolices. The response is measured bt the number mice cleared. Pathology H. nana lodges itself in the intestines and absorbs nutrients from the intestinal lumen. In human adults, the tapeworm is more of a nuisance than a health problem, but in small children, many H. nana worms can be dangerous. Usually, the larvae of this tapeworm cause the most problem in children; they burrow into the walls of the intestine, and if enough tapeworms are present in the child, severe damage can be inflicted. This is done by absorbing all the nutrients from the food the child eats. Usually, a single tapeworm will not cause health issues. H. nana usually will not cause deaths unless in extreme circumstances and usually in young children or in people who have weakened immune systems. In some parts of the world, individuals who are heavily infected are a result of internal autoinfection. Prevention Good hygiene, public health and sanitation programs, and elimination of infected rats help to prevent the spread of hymenolepiasis. Preventing fecal contamination of food and water in institutions and crowded areas is of primary importance. General sanitation and rodent and insect control (especially control of fleas and grain insects) are also essential for prevention of H. nana infection. Treatment