Helminthes Tapeworms Helminthes 2 Phylums Nematodes Roundworms Turbellaria

Helminthes (Tapeworms)

Helminthes 2 -Phylums Nematodes (Roundworms) Turbellaria Free living organisms Platyhelminthes (Flatworm) 3 -Classes Trematoda (flukes) Cestodea (tapeworms)

General Characteristics: Cestodes in Greek mean girdle or ribbon. They are parasitic in all or nearly all stages of their life cycle. Majority are long, segmented and tape-like so are called tapeworms. The worm flattened dorsoventrally, creamy to white in color. Size varies from a few mm to several meters. Adult live attached to the mucosa of the small intestine of man and animals. Larval stages are parasitic in the tissues or body cavities of vertebrate or invertebrate hosts.

Parasites of man include both adult &larva. Head or scolex is provided with suckers and sometimes with hooks that serve as organs of attachment. There are 3 regions in an adult worm: 1. Scolex or head organ of attachment. 2. Neck region of growth &proliferation. 3. Proglottids or segments (immature, mature & gravid one which contain eggs). Neck + proglottids Strobila.

Head/scolex Neck Trunk/strobi la

Sexes are not separate. Body cavity is absent. Alimentary canal is entirely absent. Excretory and nervous systems are present. Reproductive system is present and complete in each segment. According to maturity of reproductive organs, three types of segments of the strobila can be recognized from the front backwards: Immature: male and female organs are not differentiated. Mature: male and female organs have become differentiated (male organs appear first). Gravid: uteri are filled with eggs (other organs are atrophied or have disappeared).

Comparison of Body Organization of Flatworms and Roundworms. Flatworm Roundworm

Scolex knob-like & provided with 4 -cupped suckers symmetrically arranged, 2 -ventrolaterally &2 dorsolaterally. In Diphyllobothrium scolex is spatulate & is provided with a long median ventral & a similar dorsal sucking groove or bothrium. As long as the scolex remains attached, a new strobila will be formed from it.

Scolex knob-like

Number of proglottids varies from 3 -4 in the Echinococcus to 1000 or more in beef tapeworm Taenia saginata & 3000 -4000 in fish tapeworm Diphyllobothrium latum.

Covered with tegument containing microvilli (microtrichs). The worm lacking a digestive system & absorb nutrients through this tegument.

The adults reside in the gastrointestinal tract, but the larvae can be found in almost any organ. Human tapeworm infections can be divided into two major clinical groups: 1) In one group, humans are the definitive hosts, with the adult tapeworms living in the gastrointestinal tract (Taenia, Diphyllobothrium, Hymenolepis, and Dipylidium). 2) In the other, humans are intermediate hosts, with larval-stage parasites present in the tissues; diseases in this category include echinococcosis, sparganosis, and coenurosis.

Each mature segment contain: 1. Excretory system: consists of paired ventrolateral and dorsolateral longitudinal canals, at frequent intervals are numerous tubules that originate from flame cells in the tissues. Genital organs: full growth & function in the mature proglottids. In most species, there is one complete set of ♂&♀organs. According to egg oviposition cestodes can be divided to two orders: 2.

Cestodes 2 -Orders Cyclophyllidea Pseudophyllidea

I. Order Cyclophyllidea Characteristics: Large or small worms consisting of chains of segments. Scolex is quadrate with four cup-like round suckers. An apical rostellum with hooklets may be present. Vitelline glands concentrated in a single mass. Common genital pore is marginal (on lateral side of segment). No uterine opening for the exit of eggs from the gravid uterus. Eggs only escape from the rupture or disintegration of ripe segments. Eggs are not operculated and can develop only in the intermediate host, fully embryonated. Oncosphere is never a ciliated embryo. Larval development proceeds in one intermediate host.

I. Order Cyclophyllidean cestodes: Adult Worms in the Intestine: Taenia saginata Taenia solium Hymenolepis nana Hymenolepis diminuta Dipylidium caninum Larval Stages in Man: Hydatid cyst of Echinococcus granulosus and Echinococcus multilocularis Cysticercus cellulosa of Taenia solium Coenurus cerebralis of Multiceps multiceps Coenurus glomeratus of Multiceps glomeratus

Generalized Cyclophyllidean Life Cycle Adults in DH SI Egg with Onchosphere/Hexacanth Embryo Larva (Cysticercoid, cysticercus, coenurus, hydatid) in IH Adults in DH SI

II. Order Pseudophyllidea Characteristics: Large worms consisting of a long chain of segments. Scolex “head” has two slit-like sucking grooves called bothria instead of suckers. Vitelline glands are widely scattered in the parenchyma and is composed of many acini. Genital pores are on the ventral surface of the segment and are not marginal. Uterus opens to the exterior through which eggs come out Eggs are operculated and can develop only in water; immature when oviposited (unembryonated) and oncosphere gives rise to ciliated embryo. Larval development proceeds in two intermediate hosts: First larval stage is called procercoid. Second larval stage is called plerocercoid.

II. Pseudophyllidean cestodes: Adult worms in Intestine Diphyllobothrium latum: Fish Tapeworm. Larval stages: Plerocercoid in Man Sparganum mansoni Sparganum proliferum

Differences Between a Pseudophyllidean and a Cyclophyllidean Cestode Pseudophyllidean Cyclophyllidean Head or scolex Bears 2 slit-like grooves Bears 4 cup-like suckers uterus No branching Branching Convoluted uterine tubes assume the form of rosettes Uterine pore present absent Common genital pore Ventral; in the midline lateral Eggs Operculated; gives rise to Not operculated; do not ciliated larvae give rise to ciliated larvae

Common Tapeworm Infections LAB. TAPEWORM DISEASE TRANSMISSION OF INFECTION LOCATION OF ADULT IN HUMANS LOCATION OF LARVA IN HUMANS Taenia saginata taeniasis ingestion of larva in undercooked beef Small Intestine not present Taenia solium- taeniasis ingestion of larva in undercooked pork Small Intestine not present (except in autoinfection: , small intestine) DIAGNOSIS vague digestive disturbance vagues digestive disturbance s eggs or proglottids in stools subcutaneous muscles brain, eyes depending on locality: from none to epilepsy Xray, CT, MR I Serology eggs in stools ADULT Taenia solium. LARVA (cysticercus cellulosae) CLINICAL PICTURE Cysticercosis ingestion of egg Hymenolepis nana hymenolepiai s ingestion of egg Small Intestine Intestinal Villi Enteritis diarrhoea Echinochoccus granulosus hydatid disease ingestion of egg not present Liver, lungs, Bones etc depending on locality eggs or proglottids in stools X-ray, CT, US Serology Hydatid sand