Cestode (tapeworm,绦虫 )

     Taxonomic position Phylum platyhelminthes

Class Cestoda

Order Cyclophyllidae

Order Pseudophyllidae

    

GENERAL INTRODUCTIONS

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

Body wall: Tegument and

subtegument (syncytial layer);

no coelomic cavity Monoecious Digestive system: completely

degenerated

MORPHOLOGICAL FEATURES

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 eggcoracidium procercoid plerocercoid(sparganum) adult worm

Spirometra mansoni – cause sparganosis Diphilobothrium latum – accidental infection in

humans

copepod

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

LIFE CYCLE PATTERNS

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.

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 )

GENERAL INTRODUCTION

• Worldwide distribution • Large tapeworm • Larval infection of Taenia solium may cause

serious clinical disease ---CYSTICERCOSIS

Taenia solium

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. saginataThe 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

man

Egg

Egg man

auto-infection internal

external

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).

subcutaneous nodules

Cysticercus on the eyeground

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

High prevenlence Medium prevelenceLow or no prevelenceEpidemic limited areaData unavialable

World-wide distribution.Epidemic in central and south America (Mexico), Africa,

South-east Asia, eastern Europe, Micronesia .

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

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

LIFE CYCLE

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

T.saginata is prevalent in regions where cattle are raised: Africa, Middle-East, Central and South America, Europe and Asia.

DISTRIBUTION

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