Parasitology Exam 2: Cestodes Flashcards by Tori Bertsch

What is another name for Cestodes?

Tapeworms

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Scolex

head of cestode for attachment

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Rostellum

crown of the scolex, may be smooth or have hooks

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Proglottids

Segments that comprise the body of the tapeworm

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Stobila

Body of the worm comprised of proglottids and scolex

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Hermaphroditic

Organisms contain both male and female reproductive organs

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Integument

Outer covering/skin of the organism that absorbs food

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Oncosphere

Larva tapeworm within an embryonic envelope (infective stage)

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Hexacanth embryo

6-hooked larva NOT enclosed in an embryonic envelope

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List the names of intestinal cestodes:

D. latum (broad fish tapeworm)
D. caninum (cat/dog tapeworm)
H. nana (dwarf tapeworm)
H. diminuta (rat tapeworm)
T. solium (pork tapeworm)
T. saginata (beef tapeworm)

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What is the largest human tapeworm?

D. latum

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Tapeworms sexuality

Hermaphroditic

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T/F: Cestodes generally require one or more intermediate hosts for the completion of their life cycle.

True

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Specimen type for cestodes

Fresh or preserved stools for O&P

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List a notable difference between cestodes and nematodes

Cestodes are hermaphroditic, while nematodes have separate sexes

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What is another name for D. latum?

Broad fish tapeworm

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Describe the life cycle of D. latum

AQUATIC LIFESTYLE
- Crustaceans (intermediate host) ingest coracidium larva which develops into procercoid larva.
- Fish (reservoir host) ingest the procercoid larva which develops into the plerocercoid larva.
- Humans (Definitive host) ingest fish infected with the plerocercoid larva which develop into adult worms in the small intestine.

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Which is the only cestode to have an aquatic lifestyle?

D. latum

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What disease does D. latum cause?

Diphyllobothriasis - may decrease host vitB12 levels –> pernicious anemia

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Lab ID of D. latum

Visualization of eggs and/or proglottids in feces

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Describe D. latum proglottids

Wider than long
Rosette-shaped central uterus

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Describe D. latum scolex

Two shallow sucking grooves: bothria

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Describe D. latum eggs

Operculated - lid at the end with knob at opposite end

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Infective and diagnostic stage of D. latum

Diagnostic: eggs in feces
Infective: procercoid larva

Which cestode has a cucumber seed appearance when they are wet, and grain of rice appearance when dry?

D. caninum (cat or dog tapeworm)

D. caninum scolex

Rostellum - 4 to 7 rows of small hooklets

Lab ID of D. caninum

proglottids or egg packets in the stool

Infective and diagnostic form of D. caninum

Infective: cysticercoid larva Diagnostic: prolottids/egg packets in feces

How is D. caninum transmitted?

Accidental ingestion of fleas

What is the most common tapeworm? Where is it most prevalent?

H. nana; Southern US

What is different about H. nana from other tapeworms?

Intermediate host is NOT required, can be spread from person to person

Infective and diagnostic stage of H. nana

Infective: ingestion of eggs Diagnostic: eggs in feces

Which cestode eggs are infectious and should be handled carefully?

H. nana, T. solium

Describe H. nana eggs

4-8 polar filaments Double membrane Oncosphere has 6 hooks

What population is most commonly infected with H. nana?

children

How to differentiate H. nana from H. diminuta?

H. diminuta eggs lack polar filaments and are larger

Diagnostic and infective stage of H. diminuta

Diagnostic: eggs in stool Infective: Cysticerci in body cavity of insect ingested by rodent or human

Life cycle of H. diminuta

Ingestion of arthropod infected with cysticercoids --> adult worms mature in intestine --> release of eggs associated with rodents

T. solium alternate name and transmission

pork tapeworm Ingestion of raw or undercooked pork

Which cestode is both a tissue and intestinal parasite?

T. solium

T. solium/T. saginata infective and diagnostic stage

infective: cysticercus larvae in tissue diagnostic: eggs or proglottids in stool

T. solium disease

Taeniasis Cysticercosis - organism forms cysts within host tissue outside of the intestine Neurocysticercosis - organism forms cysts within tissues of the CNS

T. solium and T. saginata eggs

striated shell Cannot differentiate the two species' eggs

What is special about the therapy for T. solium?

Explusion of the scolex MUST be verified to assume satisfactory treatment

T. saginata alternate name and transmission

Beef tapeworm Ingestion of cysticerci in raw or undercooked beef

Intermediate host and definitive host of T. solium and T. saginata

T. saginata intermediate host = cattle T. solium intermediate host = pigs both definitive hosts = humans

T. saginata proglottids vs T. solium proglottids

T. saginata: 12-30 lateral uterine branches on each side T. solium: 7-13 lateral uterine branches on each side

T. saginata vs T. solium scolex

T. saginata does not contain hooklets, no rostellum T. solium has 4 suckers with hooks in a double row

Describe cestodes as a whole.

Long, segmented, ribbonlike body Hermaphroditic - no separate sexes (asexual reproduction)

What is different about tissue cestodes?

Tissue cestodes do NOT reach the adult stage in the human host (AKA humans are not the definitive hosts) Organisms infect the human in their intermediate or cyst stage

What are the two tissue cestodes discussed:

T. solium (pork tapeworm) E. granulosus

What disease does T. solium cause?

Cysticercosis Most damage is caused by the severe inflammatory host response after the cysticerci have died

Lab ID of tissue infected T. solium

ID of cysticerci in tissue

Which is the smallest of all tapeworms?

E. granulosus

What is the definitive host of E. granulosus? What is the intermediate/accidental host?

Definitive: dogs Intermediate/accidental: humans Humans are dead end hosts --> life cycle is unable to continue

What cestode is associated with hydatid cysts? Where do these hydatid cysts mostly occur?

E. granulosus Mostly occur in the liver causing cholangitis and cholestasis

Infective and diagnostic stage of E. granulosus

Infective: ingestion of eggs/cysts Diagnostic: ID of hydatid cysts in infected organ and positive serologic tests

Which organism is this associated with: Ultrasound, MRI, and CT have improved the diagnosis and may provide visualization of the fluid-filled cysts. Calcified cysts may be visualized in x-rays.

E. granulosus