Taenia is a flat worm that is commonly called tapeworm because of its flat and ribbon-like body. Taeniasolium is the pork tapeworm and the secondary host is pig, while T. saginata is the beef tapeworm whose secondary hosts are cows, buffalos, sheep and goat.
Adult tapeworm lives in the small intestine of man attached to the intestinal mucosa by its scolex. The larval stage occurs in the tissues of the secondary host which is usually pig but sometimes other animals also.
MORPHOLOGY
T. solium is long, whitish, dorsoventrally flattened and ribbon-like worm that can reach a length of 2-3 meters. Body is divided into hundreds of segments called proglottids.
There are three regions in the body, the scolex, unsegmented neck and the segmented posterior region called strobila.
Scolex is the anterior end of the body; about 1mm in diameter with 4 cup-like suckers and an anterior rounded portion called the rostellum having 20-30 curved chitinous hooks, which are used for attachment to the intestinal wall of the host.
Neck is short, narrow and unsegmented area behind the scolex. This is the growth zone or area of proliferation where new segments or proglottids are added to the body.
Strobila forms the bulk of body and consists of a series of proglottids arranged in a linear fashion. The strobila may contain as many as 800-900 proglottids. Proglottids are self-contained units, each with a complete set of both male and female reproductive organs and a part of excretory and nervous systems. The youngest proglottid is just behind the neck and the oldest is at the posterior end of strobila.
The immature proglottids on the anterior region are devoid of reproductive organs, while those in the middle region bear male reproductive organs only and are termed matureproglottids. Behind this region proglottids develop female reproductive organs also and are, therefore, hermaphrodite. Gravidproglottids towards the posterior side of strobila possess no reproductive organs but contain branched uterus packed with fertilized eggs.
Gravid proglottids regularly detach from the posterior end of strobila and pass out with host faeces. Shedding of gravid proglottids is called apolysis. The excreted proglottids with human faeces are consumed by pig.
ANATOMY
SKIN
The skin serves to protect the internal organs and also absorbs nourishment from the host’s intestine. The muscles of body wall enable body movements of the worm.
The outermost, thick, waxy covering of the body is cuticle under which is the basement membrane. Outer layer has villi-like microtrichia that help in increasing the surface area of absorption of nourishment from the host intestine. Circular and longitudinal muscles are present under the cuticle. A large number of long-necked subcuticular epidermal cells are found in the mesenchyme, which opens just below the basement membrane to form syncytium. They also secrete cuticle. Mesenchyma forms a packing material around the internal organs of the body.
DIGESTIVE SYSTEM
The alimentary canal is absent and mode of nutrition is saprozoic. Digested food is absorbed directly from the host intestine of the host through its general body surface. The digested nutrients like glucose, amino acids, glycerol etc. from the host intestine diffuse directly through its skin. The reserve food is stored as glycogen and lipids in the parenchyma.
RESPIRATORY SYSTEM
Since there is no free oxygen in intestine, respiration is anaerobic. The energy is derived from the breakdown of glycogen, giving off energy, carbon dioxide and fatty acids. The carbon dioxide is diffused out through the body surface, while fatty acids are removed by the excretory system.
NERVOUS SYSTEM
Nervous system of consists of two cerebral ganglia in the scolex connected together by a thick transverse nerve and a cerebral nerve ring. There is another rostellar nerve ring that has a pair of rostellar ganglia in rostellum. These two rings are interconnected by eight nerves. The suckers and rostellum are supplied by the nerve fibres from cerebral and rostellar ganglia. From the posterior side of the brain complex, five pairs of longitudinal nerve cords arise to extend to the length of body. Out of these two lateral longitudinal nerves are best developed. The longitudinal nerve cords are connected in each proglottid by a ring connective situated below the transverse excretory canal.
Sense organs are absent in tape worm but free nerve endings are abundant in the scolex and rest of the body.