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 Spirometra mansoni – cause sparganosis 1. Pseudophyllidae type Scolex provided 2 grooves - bothrium Need two intermediate hosts aquatic crustaceans fish or other vertebrate animals Life stages eggcoracidium  procercoid plerocercoid(sparganum)  adult worm Spirometra mansoni – cause sparganosis Diphilobothrium latum – accidental infection in humans copepod

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

Larval stage of a cestode that develop in the intermediate host. 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. Different species of cestode may have different types of metacestode stage

Important species Taenia solium Teania saginata Echinococcus granulosus Spirometra mansoni Hymenolepis nana Hymenolepis diminuta Important species

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 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 Egg man 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 Scolex Mature Proglottid Gravid proglottid Intermediate Host Disease caused Infective stage Mode of infection Diagnosis Clinical significance Chemotherapy 2-4m Rostellum & hooks 3 lobes of ovary Uterine Branches<13 Swine & Human Taeniasis & cysticercosis Egg & Cysticercus Cross or autoinfection Egg may be found in stool Much more important Should be instant 4-8m No 2 lobes of ovary >15 Cattle Taeniasis only Cysticercus Only Cross only Perianal egg exam Less than T. solium Not so urgent