Parasitology Exam 2: Cestodes Flashcards
What is another name for Cestodes?
Tapeworms
Scolex
head of cestode for attachment
Rostellum
crown of the scolex, may be smooth or have hooks
Proglottids
Segments that comprise the body of the tapeworm
Stobila
Body of the worm comprised of proglottids and scolex
Hermaphroditic
Organisms contain both male and female reproductive organs
Integument
Outer covering/skin of the organism that absorbs food
Oncosphere
Larva tapeworm within an embryonic envelope (infective stage)
Hexacanth embryo
6-hooked larva NOT enclosed in an embryonic envelope
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)
What is the largest human tapeworm?
D. latum
Tapeworms sexuality
Hermaphroditic
T/F: Cestodes generally require one or more intermediate hosts for the completion of their life cycle.
True
Specimen type for cestodes
Fresh or preserved stools for O&P
List a notable difference between cestodes and nematodes
Cestodes are hermaphroditic, while nematodes have separate sexes
What is another name for D. latum?
Broad fish tapeworm
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.
Which is the only cestode to have an aquatic lifestyle?
D. latum
What disease does D. latum cause?
Diphyllobothriasis - may decrease host vitB12 levels –> pernicious anemia
Lab ID of D. latum
Visualization of eggs and/or proglottids in feces
Describe D. latum proglottids
Wider than long
Rosette-shaped central uterus
Describe D. latum scolex
Two shallow sucking grooves: bothria
Describe D. latum eggs
Operculated - lid at the end with knob at opposite end
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
