Upload
simon-welch
View
233
Download
7
Embed Size (px)
Citation preview
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