Parasitology - Intestinal Cestodes

Front 1

Cestodes are true tapeworms that possess the following structures:

Back 1

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

Front 2

Cestodes of human importance include: (6)

Back 2

1. Taenia saginata
2. Taenia solium
3. Diphyllobothrium latum
4. Hymenolepis nana
5. Hymenolepis dimminuta
6. Dipylidium caninum

Front 3

The live cycle of the cestodes involves a ___ except in the case of ___

Back 3

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)

Front 4

Taenia tapeworm infections are aquired by humans via __

Back 4

ingestion of larval infected, poorly cooked pork (T. solium) or beef (T. saginata)

Humans serve as the definitive host

color plate 22-6D

Front 5

Humans can also serves as an intermediate host for Taenia _____, but not Taenia ____

Back 5

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

Front 6

Human cysticercosis does not occur with Taenia ___

Back 6

T. saginata

Front 7

Cysticercosis has a high prevalence in __

Back 7

Mexico and Latin America

Front 8

The life cycle of T. solium includes

Back 8

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

p.1283

Front 9

Laboratory identification of Taenia tapeworm infection is usually via __

Back 9

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

Front 10

Features of Taenia tapeworm eggs

Back 10

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

Front 11

Adult Taenia are distinguished by ___

Back 11

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

Front 12

Taeniasis (intestinal infection) is usually ___

Back 12

asymptomatic, detected by passage of proglottids in stool

Follows ingestion of undercooked pork or beef (can be seen with T. solium and T. saginata)

Front 13

Cysticercosis refers to the development of ___

Back 13

Extraintestinal encysted larval forms of T. solium

Follows ingestion of gravid proglottids or eggs in fecally contaminated food or water

Front 14

In humans with cysticercosis, 60-96% of patients exhibit involvment of the ___

Back 14

CNS (neurocysticercosis)

Front 15

Neruocysticercosis is the leading identifiable cause of ___ in young adults living in endemic areas.

Back 15

Epilepsy

Front 16

Test used to confirm suspected cases of cysticercosis

Back 16

Indirect hemagglutination serologic assay available through the CDC

Front 17

The giant fish tapeworm (aka___) uses ___ intermediate hosts

Back 17

Diphyllobothrium latum

two

Front 18

D. latum is endemic in ___

Back 18

Cold clear lake regions
Including upper Midwest of the US, Canada, and Alaska

Front 19

The life cycle of D. latum includes

Back 19

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

p.1285

Front 20

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

Back 20

20 years

Minimal symptoms

Front 21

In a minority of patients with D. latum infection, __ can develop

Back 21

megaloblastic anemia secondary to vitamin B12 deficiency (selective competition with D. latum)

Front 22

Humans can develop sparganosis, with the development of pruritic subcutaneous nodules, due to ___

Back 22

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

Front 23

D. latum proglottids are rarely passed in the stool, but have a characteristic morphology __

Back 23

They are broader than they are long (latum is latin for broad)

Scolex is rarely seen in stool too

Front 24

Laboratory diagnosis of D. latum infection is usually made by __

Back 24

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

Front 25

Hymenolepis nana (aka __) is seen worldwide and is one of the more common cestode infections of humans

Back 25

Dwarf tapeworm

Front 26

Hymenolepis diminuta is primarily a parasite of ___ and ___ found in humans

Back 26

rats and mice (rodents)

uncommonly

Front 27

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

Back 27

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

Front 28

Infections with D. latum and Taenia tapeworms is commonly due to only ___ worm, in contrast, Hymenolepiasis can be due to ___

Back 28

1. one worm

2. up to 1000 worms

Front 29

Hymenolepiasis is a serious infection in immunocompromised due to the risk of __

Back 29

Autoinfection

Ova hatch in the intestine and reinfect the human host

Front 30

Laboratory diagnsois of Hymenolepiasis is usually due to___

Back 30

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

Front 31

Adult Hymenolepis tapeworms measure no longer than __

Back 31

1.5 inches

Front 32

Dipylidium caninum has a similar life cycle to that of ___

Back 32

Hymenolepis diminuta

Front 33

Humans are an ____ host for Dipylidium caninum

Back 33

accidental

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

Children more commonly

Often asymptomatic or minimal symptoms

Front 34

In the human, Dipylidium caninum larvae penetrate the intestinal mucosa and __

Back 34

develop into adults in the intestine

Front 35

Laboratory identification of Dipylidum caninum infection in humans is made by

Back 35

Identification of characteristic egg packets in fecal material

15-25 globular eggs, each egg contains an oncosphere with six hooklets

Front 36

Proglottids of Dipylidium caninm tapeworms are identified based on __

Back 36

presence of two (double) genital pores, hence the name Dipylidium

color plate 22-6O and P