Cestodes

Question 1

Name the 2 taenia species that have human definitive hosts.

Answer 1

Taenia saginata
Taenia solium

Question 2

Describe taenia saginata.

Answer 2

• Cyst/metacestode in muscle of cattle IH
• No hooks on rostellum
• Endemic in UK

Question 3

Describe taenia solium.

Answer 3

• Cyst/metacestode in muscle of pig IH.
• Has hooks on rostellum
• Not endemic in UK
• More dangerous, associated with poor sanitation in pig keeping
• Ingestion of eggs direct from another human > neurocysticercosis

Question 4

Outline the taenia lifecycle in humans.

Answer 4

1. Adult in human intestines
2. Eggs/proglottids passed in faeces
3. Eggs survive up to 9 months
4. Eggs ingested by cattle or pigs
5. Cyst forms in human
6. Human ingests cyst in undercooked beef or pork
7. Encysts in stomach to release head to attach to the intestine

Question 5

What are the hosts of taenia hydatigena?

Answer 5

DH = dog
IH = sheep, cattle, pig, horse

Question 6

Outline the lifecycle of taenia hydatigena.

Answer 6

1. Adult lives in canine host intestines
2. Eggs/proglottids shed onto pasture in faeces
3. Ingested by IH
4. Oncospheres released in digestion
5. Larvae migrate to predilection sites. Migrates via the liver for 4 weeks
6. Cyst/metacestode

Question 7

Distinguish taenia and dipylidium caninum eggs.

Answer 7

Taenia eggs containing hexacanth embryo/oncosphere with 3 pairs of hooks

Dipylidium caninum eggs packet containing 25-30 eggs

Question 8

Describe echinococcus granulosus.

Answer 8

• Adult in carnivore
• DH = dog
• Hydatid cyst in IH in liver and lungs
• IH = sheep, human, cattle, horse, pig

Question 9

Describe echinococcus multilocularis.

Answer 9

• Adult in carnivore
• DH = dog
• Alveolar hydatid/multilocular cyst in liver of IH. can spread and metastasise to the brain
• IH = human and rodent

Question 10

What are the hosts of anoplocephala perfoliata?

Answer 10

DH = horse
IH = forage mite

Question 11

Outline the lifecycle of anoplocephala perfoliata.

Answer 11

1. Horse sheds proglottids with eggs in faeces
2. Mite takes up where infective cysticercoid larvae develop
3. Horse consumes mites off grass
4. Larvae attach to intestine to develop into adult

Question 12

What is the site of anoplocephala perfoliata?

Answer 12

Ileo-caeco-colic junction

Question 13

What are the side effects of anoplocephala perfoliata in large numbers?

Answer 13

Colic
Ulcers
Intestinal obstruction
Blockage

Question 14

What are the hosts of monezia expansa?

Answer 14

DH = cattle, deer, sheep
IH = forage mite

Question 15

Outline the lifecycle of monezia expansa.

Answer 15

1. DH sheds eggs onto pasture in faeces
2. Mite ingests egg
3. Cysticercoids develop within mite
4. DH ingests mite grazing
5. Adult develops from those cysticercoids

Question 16

What are the hosts of dipylidium caninum?

Answer 16

DH = dog, fox, cat
IH = ctenocepahlides/flea or trichodectes/lice

Question 17

What are the side effects on the DH of dipylidium caninum.

Answer 17

Anal discomfort, itching - must flea control

Question 18

Describe the structure of the dipylidium caninum adult.

Answer 18

Double genital pore, looks like rice grains, small scolex, less than 80cm

Question 19

Outline the lifecycle of dipylidium caninum.

Answer 19

1. Adult in DH intestine
2. Egg packets shed
3. Flea larva with cysticercoid become adult flea with cysticercoid become adult flea with cysticercoid
4. Dog ingests

Question 20

Name and describe 3 forms of tapeworm metacestode.

Answer 20

Cysticercus - single scolex

Coenurus - multiple scolices

Hydatid - endogenous and exogenous cysts that can spread

Question 21

Describe the basic tapeworm structure.

Answer 21

Scolex - has suckers attaches to intestine of host

Stroblia - proglottid segments that start immature near head then mature down the tail