CLASS CESTODA (Tapeworms)

Cestoda (Cestoidea) is a class of parasitic flatworms Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork (Taenia solium), beef (T. saginata), and fish (Diphyllobothrium spp.), or if they live in, or eat food prepared in, conditions of poor hygiene (Hymenolepis orEchinococcus species).

The cestodes, or tapeworms, differ in a from other worms. Their bodies are long and flat, made up of many segments called proglottids. Digestive tracts are absent completely. At the tapeworm's anterior end is a specialized segment called a scolex, which is usually covered with hooks or suckers and serves to anchor it to the host.

General characters of cestodes 1.Ribbon-like (Tapeworms). 2.Flattened. 3.Alimentary canal absent. 4.Has no body cavity. 5.Segmented into Scolex, neck and segments. 6.Cestodes are hermaphrodites.

­PSEUDOPHYLLIDEACYCLOPHYLLIDEA Scolex Organsof attachment Elongated Bothria Globular Suckers and hooks Mature segment Genital pore Uterus Gravid segment Ventral Open ventrally Absent Lateral Blind Present Eggs Operculated, Immature Need water to develop Non-operculated, Mature Do not need water Interemediate hosts Larval stages Two hosts Solid larvae: 1. Procercoid 2. Plerocercoid `One host Cystic larvae: Cysticercus MembersDiphyllobothrium latwnTaenia saginata Taenia solium Hypenolepis nana Hymenolepis diminuta Echinococcus granulosus

Tapeworm may be classified into two groups: A.Intestinal tapeworms (adult cestodes). B.Tissue tapeworms (larval cestodes).

INTESTINAL TAPEWORMS DIPHYLLOBTHRIUM LATUM (Fish worm)

Disease: Diphyllobotheriasis Transmission: By ingesting the infective larvae which is known as a plerocercoid in raw or insufficiently cooked freshwater fish. Habitat: The small intestine of man and other fish eating mammals.

Morphology: Adult worms are up to 15 meters in length. Scolex - almond shaped Eggs - measure 30 x 60 microns, and exhibit an operculum (this is the only cestode with an operculated egg).

Life cycle: The adult worms lives in the small intestine of man (Definitive host) and fish-eating animals (Reservoir hosts). Immature eggs (Diagnostic stage) pass in faeces. In fresh water, coracidium develops in about 2 weeks hatches and swims in water. The coracidia are ingested by cyclops (1st. I.H.) and develops to onchosphere which migrates to body cavity and change to procercoid larva in about 2 weeks. When the infected cyclops is swallowed by fresh water fish as Salmon (2nd. I.H.) procercoid passes form intestine of fish to muscles and changes to plerocercoid larva, in about 2 weeks. Man gets infected by eating such undercooked or smoked fish containing the plerocercoid larva (the infective stage). The larva becomes attached to mucosa and gives an adult.

Clinical Features and Pathogenicity: 1.D. Latum may cause gastrointestinal symptoms, weakness, weight loss. 2.Toxaemia due to toxic metabolites of the worms. 3.Intestinal obstruction due to large number of worms. 4.Megaloblastic anaemia may develop due to uptake of vitamin B 12 by the tapeworm in competition with the host

Laboratory Diagnosis: : 1.Finding the operculated eggs in faeces. 2.Occasionally detection of mature segments in faeces

Treatments: 1.Praziquantel (Biltricide, Distocide): mg/kg as a single oral dose. 2.Niclosamide (yomesan): 4 tablets (2g) chewed in a single dose on empty stomach. 3.Vitamin B 12 : should be given parenterally in case of anaemia

Prevention and Control: *Proper cooking of freshwater fish (at least 56  C for 5 minutes), prolonged salting or freezing at - 10  C for 72 hours. R. H must be dewarmed *Sanitary disposal of faeces.