| General Features | Adult dwells as internal parasite in the small intestine of man, where it is anchored to intestinal mucosa by its scolex. Larval stage occurs in the tissues of a intermediary phase. Body is 1-5 m long, flattened like a ribbon. Narrow anteriorly and gradually broadens towards the posterior end. Divided into great number of Proglottids (not true metameric segments). Scolex: Represents the anterior region of the body. Knob-like, bilaterally symmetrical. Rostellum: Prominent rounded cone at the apex. Hooks: Arranged in 2 rows around base of Rostellum. Hooks of anterior circle are larger. Broadest part of Scolex has 4 hemispherical suckers. With the help of Scolex, Taenia lies buried in the intestinal mucosa, providing firm adhesion to the body against the loosening action of peristaltic movements of the host’s intestine. It plays no role in perceiving or catching food. Parasitic Adaptations: External body covering or tegument is freely permeable to water and nutrients, but protects against digestion why host’s alkaline juices. Internal Osmotic pressure is higher than that of the surrounding host fluid. pH tolerance is high. Adult as well as larva lack cilia and other organs of locomotion, as they are not needed. Scolex with suckers and spines, serves for attachment with the epithelial lining of the host intestine. Alimentary canal is absent as it absorbs digested food. Circulatory, respiratory and sensory systems are absent. Nervous system is poorly developed. Respiration is anaerobic as free oxygen is not available. Reproductive system is immensely developed and enables production of large number of eggs. Hermaphroditism and Proglottisation ensures self-fertilisation within the same Proglottid or cross-fertilisation with another Proglottid, in the same worm. Resistant covering, shell or capsule around zygotes and embryos provides protection from unfavourable conditions. |
| Life History | Development begins within parent’s body. Zygote develops into a six toothed hexacanth, which together with protective covering is called Onchosphere. Ingested by pig host. Hexacanth loses protective envelope, bores into blood vessels of gut and migrates voluntary muscles, where it encysts as Cysticercus. Man acquires infection by eating inadequately cooked pork containing Cysticercus. |
| Pathogenicity | Taeniasis Man acquires infection by eating uncooked pork that contains Cysticerci. These develop into adult tapeworms in the intestine. Presence of tapeworms in intestine causes gastro-intestinal disorders. Anaemic conditions may develop. Treatment: Atabrin drug, only eat thoroughly cooked beef or pork. Hydatid Disease Due to Echinococcus granulosus Primary host is Dog. Pass out in faeces and develop into Onchospheres. Man acquires infection on ingesting food or water contaminated with Onchospheres. Cysts develop in liver, lungs etc. In brain and kidney, cysts can be fatal. Treatment: Atabrin drug |