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Cestode (tapeworm,绦虫) GENERAL INTRODUCTIONS Taxonomic position Phylum platyhelminthes Class Cestoda Order Cyclophyllidae Order Pseudophyllidae MORPHOLOGICAL FEATURES Flat and Segmented Scolex-equipped with organs of attachment: suckers, hooks, grooves Neck - germinal portion Strobila: Proglottids Immature proglottid Mature proglottid gravid proglottid MORPHOLOGICAL FEATURES Body wall: Tegument and subtegument (syncytial layer); no coelomic cavity Monoecious Digestive system: completely degenerated PHYSIOLOGY AND PATHOGENESIS Surface absorption capabilities Highly developed reproductive functions Anaerobic metabolism All species are parasitic Pathogenic stage may be adult or the larva LIFE CYCLE PATTERNS 1. Pseudophyllidae type Scolex provided 2 grooves - bothrium Need two intermediate hosts aquatic crustaceans fish or other vertebrate animals Life stages copepod eggcoracidium procercoid plerocercoid(sparganum) adult worm Spirometra mansoni – cause sparganosis Diphilobothrium latum – accidental infection in humans LIFE CYCLE PATTERNS 2. Cyclophyllidae type Scolex provided 4 suckers sometimes supplemented with circular of hooks Need one intermediate host only -- usually mammals Life stages egg hexacanth metacestode stage adult worm. Taenia solium Teania saginata Echinococcus granulosus E. multilocularis Hymenolepis spp Metacestode stage Larval stage of a cestode that develop in the intermediate host. Cysticercus - Taenia spp. Hydatid cyst - Echinococcus granulosus Alveolar hydatid cyst - E. multilocularis Cysticercoid - Hymenolepis spp. Important species Taenia solium Teania saginata Echinococcus granulosus Spirometra mansoni Hymenolepis nana Hymenolepis diminuta Taenia solium (猪带绦虫) Taenia saginata (牛带绦虫) Taenia solium GENERAL INTRODUCTION • Worldwide distribution • Large tapeworm • Larval infection of Taenia solium may cause serious clinical disease ---CYSTICERCOSIS Morphology Can be up to 2 to 4 meters long It has a globular scolex with four suckers and 2 circular rows of hooks (rostellum) The gravid proglottids are 5×10 mm with a 7-13 branched uterus The eggs of T. solium and T. saginata are indistinguishable scolex of T. solium. Gravid proglottids of Taenia solium. Injection of India ink in the uterus allows visualization of the primary lateral branches. T. solium has 7 13 branches on each side. Note the genital pores in mid-lateral position. Taenia solium eggs of Taenia solium and T. saginata The eggs are rounded or subspherical, diameter 31 - 43 µm, with a thick brown embryophore. Inside each egg is an embryonated oncosphere with 6 hooks. A complete egg always has the primary membrane (shell) that surrounds eggs. Cysticercus Life cycle of T.solium Main points of the life cycle Man is the only definitive host, but he can also be the intermediate host for T.solium Pig is the important intermediate host for T.solium Adult worm reside in the lumen of the upper part of small intestine The infective stage to man are both egg/gravid proglottid and cysticercus for T.solium A tapeworm larval cyst (cysticercus) is ingested with poorly cooked rice-like meat The larva escapes the cyst and passes to the small intestine where it attaches to the mucosa by the scolex suckers The proglottids develop as the worm matures in 3 to 4 months Main points of the life cycle The adult may live in the small intestine as long as 25 years and pass gravid proglottids with the feces When eggs consumed by pigs in which they hatch and form cysticerci T.solium eggs can also infect humans and cause cysticercosis (larval cysts in lung, liver, eye, maxillofacial region and brain) Eggs from ----auto-infection, external Eggs from ----auto-infection, internal Eggs from ----external auto-infection internal man Egg man external Egg auto-infection external Pathogenesis and clinical features Adult worm —Teaniasis Light infections remain asymptomatic Heavier infections may produce abdominal discomfort, epigastric pain, vomiting and diarrhea Metacestode stage –Cysticercosis The cysticercus stage of T. solium can be found anywhere in the body -- subcutaneous, muscles, eye, brain Regardless of the tissue affected, pathological consequences are those of a space-occupying lesion Cysticerci in brain tend to grow a larger size than those in other tissues The process of calcification may be accompanied by the release of antigens -- inflammatory reaction Cysticercosis The incidence of cerebral cysticercosis can be as high 1 per 1000 population and may account for up to 20% of neurological case in some countries (e.g., Mexico); cysticercosis ocular involvement occurs in about 2.5% of patients and muscular involvement is as high as 10% (India). Cysticercus on the eyeground subcutaneous nodules pseudohypertrophy of muscle Cysticerci in brain Cysticerci in heart Cysticerci in tongue DIAGNOSIS For adult worm infection (Teaniasis) ＊ History of eating raw pork ＊ Find gravid proglottids in feces ＊ Perianal swab to find eggs For cysticercosis ＊ Specific diagnosis is difficult to establish, the history and adult worm infection attribute to strong suspicion ＊ Biopsy to subcutaneous lesions ＊ Computerized axial tomography or magnetic resonance imaging ＊ Serological examination for specific antibody Epidemiological distribution World-wide distribution. Epidemic in central and south America (Mexico), Africa, South-east Asia, eastern Europe, Micronesia . High prevenlence Medium prevelence Low or no prevelence Epidemic limited area Data unavialable PRINCIPLES OF CONTROL Treat all patients to eradicate the source of larvae parasitism Pumpkin seed and areca nut ; Praziquantel Avoid the fecal contamination of pig feed Modernization of raising pigs Pay attention to personal and food hygiene Intensive examination of the pork Adequate cooking or freezing of meat are effective precautions cysticerci do not survive at temperatures below -10℃ and above 50 ℃. Customs of pig husbandry Teania saginata Can be up to 4 to 8 meters long The scolex with four suckers The gravid proglottids with a 15-30 branched uterus The eggs of T. solium and T. saginata are indistinguishable gravid proglottid of T. solium gravid proglottid of T. saginata LIFE CYCLE LIFE CYCLE Human is the only definitive host, cattle is the intermediate host Adult worm reside in the lumen of the upper part small intestine The infective stage to man is larva No cysticercus in human PATHOGENESIS The adult parasite induces some host reaction The process of calcification may be accompanied by the release of antigens -- inflammatory reaction DIAGNOSIS For adult worm infection Find gravid proglottids in feces or experimental inducing worm DISTRIBUTION T.saginata is prevalent in regions where cattle are raised: Africa, Middle-East, Central and South America, Europe and Asia. PRINCIPLES OF CONTROL Treat the patients --Pumpkin seed and areca nut; Praziquantel Modernization of raising cattle Intensive examination of the beef COMPARISON OF THE TWO TAPEWORMS T. solium T. saginata Size 2-4m 4-8m Scolex Rostellum & hooks No Mature Proglottid 3 lobes of ovary 2 lobes of ovary Gravid proglottid Uterine Branches<13 >15 Intermediate Host Swine & Human Cattle Disease caused Taeniasis & cysticercosis Taeniasis only Infective stage Egg & Cysticercus Cysticercus Only Mode of infection Cross or autoinfection Cross only Diagnosis Egg may be found in stool Perianal egg exam Clinical significance Much more important Less than T. solium Chemotherapy Should be instant Not so urgent
