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36 Cards in this Set

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  • Back
Cestodes are true tapeworms that possess the following structures:
Body (stroblia = scolex + proglottids)
1. Scolex "head" has a crown (rostellum) which is either armed with hooklets or unarmed
2. Proglottids (hermaphroditic, egg-producing body segments)

Color plates 22-6A and B
Cestodes of human importance include: (6)
1. Taenia saginata
2. Taenia solium
3. Diphyllobothrium latum
4. Hymenolepis nana
5. Hymenolepis dimminuta
6. Dipylidium caninum
The live cycle of the cestodes involves a ___ except in the case of ___
1. Intermediate host for the development of larva
2. Hymenolepis nana - human-to-human transmission may occur through ingestion of fecally conatminated food or water that contains infective eggs (no intermediate host required)
Taenia tapeworm infections are aquired by humans via __
ingestion of larval infected, poorly cooked pork (T. solium) or beef (T. saginata)

Humans serve as the definitive host

color plate 22-6D
Humans can also serves as an intermediate host for Taenia _____, but not Taenia ____
1. Taenia solium - in which the larvae travel widely throughout the human body via the circulation, with a propensity to lodge in the brain (neurocysticercosis)

2. Not T. saginata
Human cysticercosis does not occur with Taenia ___
T. saginata
Cysticercosis has a high prevalence in __
Mexico and Latin America
The life cycle of T. solium includes
1. Human infected with intestinal tapeworms pass proglottides and/or mature ova into external environment
2. Embyronated eggs or proglottids are ingested by a pig
3. In the pig intestine, eggs hatch releasing oncospheres
4. Oncospheres peneterate the intestinal wall, enter the circulation, migrate to skeletal muscle
5. Oncospheres encyst within skeletal muscle of the pig, forming bladder-like cysts (cysticerus)
6. Humans ingest undercooked pork with cysticerci
7. The scolex evaginates in the intestine and attaches to small intestinal mucosa
8. The tapeworm matures and produces proglottids
9. Eggs and proglottids are released into the feces

Laboratory identification of Taenia tapeworm infection is usually via __
Identifying characteristic eggs in fecal material

Only a diagnosis of Taenia tapeworm infection can be made based on eggs alone (identical for T. solium and T. saginata)

Require proglottids or scolex to identify the species
Features of Taenia tapeworm eggs
Spherical eggs with a smooth, thick shell with radial striations

May see an oncosphere with 3 pairs of hooklets

color plates 22-6 H and G
Adult Taenia are distinguished by ___
T. solium
1. (smaller) 2-4 meters in length
2. Scolex is armed (armed rostellum)
3. Proglottids exhibit <13 uterine branches

T. saginata
1. (Longer) 4-10 meters
2. Scolex is unarmed (unarmed rostellum)
3. Proglottids with >13 uterine branches

color plates 22-6B and C
Taeniasis (intestinal infection) is usually ___
asymptomatic, detected by passage of proglottids in stool

Follows ingestion of undercooked pork or beef (can be seen with T. solium and T. saginata)
Cysticercosis refers to the development of ___
Extraintestinal encysted larval forms of T. solium

Follows ingestion of gravid proglottids or eggs in fecally contaminated food or water
In humans with cysticercosis, 60-96% of patients exhibit involvment of the ___
CNS (neurocysticercosis)
Neruocysticercosis is the leading identifiable cause of ___ in young adults living in endemic areas.
Test used to confirm suspected cases of cysticercosis
Indirect hemagglutination serologic assay available through the CDC
The giant fish tapeworm (aka___) uses ___ intermediate hosts
Diphyllobothrium latum

D. latum is endemic in ___
Cold clear lake regions
Including upper Midwest of the US, Canada, and Alaska
The life cycle of D. latum includes
1. Unembryonated eggs are passed into the stool of infected humans - into freshwater
2. Eggs embryonate and hatch a coracidium
3. A crustacean (copepod or cyclops) ingests the coracidium
4. A freshwater fish ingests the infected crustacean
5. The larvae develop within the flesh of the fish
6. Humans ingest the raw or poorly cooked fish
7. Larvae develop into adults in the small intestine

D. latum can live up to __ years in the human intestine
20 years

Minimal symptoms
In a minority of patients with D. latum infection, __ can develop
megaloblastic anemia secondary to vitamin B12 deficiency (selective competition with D. latum)
Humans can develop sparganosis, with the development of pruritic subcutaneous nodules, due to ___
A diphyllobothroid tapeworm closely related to D. latum.

In this case, humans serve as intermediate host

Adult worms live in cats and dogs.

Humans ingest the crustacean (not a freshwater fish as is the case with D. latum life cycle)

The larvae then develop in the human subcutaneous tissue - pruritus, peirpheral eosinophilia

Diagnosed by demonstrating the larvae in subcutaneous tissue biopsy
D. latum proglottids are rarely passed in the stool, but have a characteristic morphology __
They are broader than they are long (latum is latin for broad)

Scolex is rarely seen in stool too
Laboratory diagnosis of D. latum infection is usually made by __
Detection of characteristic eggs in fecal material

Elongated eggs with a smooth shell, inconspicuous nonshouldered operculum, and a knoblike thickening at the other end

color plate 22-6L
Hymenolepis nana (aka __) is seen worldwide and is one of the more common cestode infections of humans
Dwarf tapeworm
Hymenolepis diminuta is primarily a parasite of ___ and ___ found in humans
rats and mice (rodents)

Hymenolepis nana life cycle is unique among the cestodes in that is does not require ___
an intermediate host

1. a larval-infected insect can serve as an intermediate host - humans ingest insect

2. more commonly, humans are infected by ingesting eggs in contaminated food or water
Infections with D. latum and Taenia tapeworms is commonly due to only ___ worm, in contrast, Hymenolepiasis can be due to ___
1. one worm

2. up to 1000 worms
Hymenolepiasis is a serious infection in immunocompromised due to the risk of __

Ova hatch in the intestine and reinfect the human host
Laboratory diagnsois of Hymenolepiasis is usually due to___
Detection of characteristic eggs

H. nana eggs: small, smooth oval eggs with a hexacanth (six hooklets) embryo, polar filaments on either side of the hexacanth membrane

H. diminuta eggs: larger, spherical, devoid of polar filaments

color plate 22-6N
Adult Hymenolepis tapeworms measure no longer than __
1.5 inches
Dipylidium caninum has a similar life cycle to that of ___
Hymenolepis diminuta
Humans are an ____ host for Dipylidium caninum

ingest dog or cat fleas that are infected with the cysticercoid form of D. caninum

Children more commonly

Often asymptomatic or minimal symptoms
In the human, Dipylidium caninum larvae penetrate the intestinal mucosa and __
develop into adults in the intestine
Laboratory identification of Dipylidum caninum infection in humans is made by
Identification of characteristic egg packets in fecal material

15-25 globular eggs, each egg contains an oncosphere with six hooklets
Proglottids of Dipylidium caninm tapeworms are identified based on __
presence of two (double) genital pores, hence the name Dipylidium

color plate 22-6O and P