Cestodes (tapeworms)

Question 1

Characteristics

Answer 1

Long, segmented, ribbon-like form
Usually live in small intestine
Absorb nutrients through cuticle; have no digestive tract
Cyclophyllidean – true tapeworms – in terrestrial food chains
Pseudophyllidean – pseudotapeworms – in aquatic food chains

Question 2

Cyclophyllidean tapeworms

Answer 2

Scolex – “head” or anterior end; may have a mobile, often retractable structure called a rostellum

“Armed” if has a # of hooks

Suckers – total of 4 on the sides
of the scolex; may be more anteriorly located on an unarmed scolex

Question 3

Strobila – body of the tapeworm

Answer 3

Consists of segments called proglottids that grow by being budded off from the neck of the scolex; therefore, the most mature proglottids are at the distal end
Reproductive organs (male & female for each segment) appear as segments mature
Genital pores usually open at the lateral margins

Question 4

Tapeworm Eggs

Answer 4

Spread by detaching a whole gravid segment full of eggs from the distal end of the tapeworm. Segment passes out in the feces – doesn’t lay eggs in the intestinal tract.
**Hard to diagnose infection unless see segments being passed.
Once outside the body, some segments discharge eggs through the genital pore; in others, the entire segment disintegrates

Question 5

Cysticercoid

Answer 5

single invaginated scolex with no fluid (usually in invertebrate IH)

Question 6

Cysticercus

Answer 6

single bladder with 1 scolex – fluid filled

Question 7

Strobilocercus

Answer 7

cysticercus that has begun to elongate and segment while still in the IH

Question 8

Cyclophyllidean metacestodes – larval forms

Answer 8

cystercercoid, cysticercus, strobilocercus, coenurus

Question 9

Coenurus

Answer 9

single fluid filled bladder with many scolices

Question 10

Hydatid

Answer 10

Cyst – contains brood capsules which release scolices. Grows slowly – usually only a few cm. in diameter in slaughter animals
Alveolar – cyst with exogenous budding – invasive – doesn’t remain contained within CT capsule – proliferates and infiltrates like a “cancer”

Question 11

Dipylidium caninum

Answer 11

flea tapeworm
Up to 50 cm long; well developed rostellum with several rows of hooks
Proglottids “cucumber seed” shaped; resemble dried rice grains when found stuck to fur or in animal’s bedding; have bilateral genital pores

Question 12

Dipylidium caninum (clinical signs, pathology)

Answer 12

Not highly pathogenic; may rarely be associated with diarrhea
Most common clinical complaint is anal pruritus (“scooting”)

Question 13

Dipylidium caninum (diagnosis)

Answer 13

Tapeworm segments perianally or in feces
Rarely see eggs in fecal exams
May do squash prep of segment to see egg packets

Question 14

Dipylidium caninum (treatment)

Answer 14

Praziquantel (Droncit®)
Epsiprantel (Cestex®)
Must also treat for fleas; prepatent period only 2-3 weeks.

Question 15

Taenia sp.

Answer 15

Adults live in small intestine of carnivores and man; IHs all mammalian (man may serve as IH as well as being infected by adults)
Several species found in dogs/cats

Question 16

Taenia sp. (morphology and egg)

Answer 16

Segments usually rectangular
Genital pores open in irregular sequences at either side
Scolex usually has an armed rostellum with a double row of hooks (except T. saginata, which is unarmed);

Egg: small, spherical with hexacanth embryo; thick shell with radial striations

Metacestode form = cysticercus

Question 17

Taenia sp (important species)

Answer 17

Taenia pisiformis – common in dogs; rabbits IHs – common in hunting and farm dogs who eat rabbits
Taenia hydatigena – dogs and wild canids; IHs ox, pig, sheep – more common in farm dogs; up to 5 meters long
Taenia taeniaeformis – cat; rodents His; prepatent period only 16-18 days

Question 18

Taenia saginata

Answer 18

Beef tapeworm of man
IHs ox, reindeer, wildebeest, etc.; encyst in muscle of IH
5-15 meters long in small intestine of man;
UNARMED scolex
greater than 100,000 eggs/gravid segment – segments crawl about spreading eggs as they go

Question 19

Taenia solium

Answer 19

Pork tapeworm of man; pig IH; up to 7 meters long; armed; man may serve as IH

Question 20

Echinococcus sp.

Answer 20

Smallest cestode – scolex and two-four segments
Double row of hooks on rostellum
Two important species

Question 21

Echinococcus granulosus

Answer 21

Hosts – dogs and other canids – no pathology
IH – usually herbivores; also pig, man, and other mammals
Importance is as zoonosis – man as IH
Lung common site for onchosphere to encyst as hydatid cyst – real danger to man
Worldwide distribution, especially sheep-raising areas

Question 22

Echinococcus multilocularis

Answer 22

Hosts – canids/felids
IH – Usually rodents and insectivores; occasionally man
Public health significance – form alveolar hydatids in man as IH

Question 23

Mesocestoides sp.

Answer 23

In some ways, a link with pseudophyllidean tapeworms
Genital pore on midline
Needs 2 IHs
Hosts – carnivores, birds, occasionally man
Example: Mesocestoides lineatus
IH I – coprophageous beetles; orabatid mites
IH II – vertebrates such as the rabbit – develop in pleural and peritoneal cavities
Small intestine in final host – no pathology

Question 24

Anoplocephalidae

Answer 24

Host range: Mammals, birds, reptiles
**Vet importance – herbivores
Unarmed scolex, segments much wider than long
Embryophore has irregular shape
Life cycle – segments from FH  eggs released  IH mites, etc.  FH ingests IH

Question 25

Horse tapeworms

Answer 25

A. magna – small intestines – 80 cm
A. perfoliata – lower small intestines, cecum, colon – 8 cm; wide, wedge-shaped, occ. Mistaken for flukes
Paranoplocephala sp. – Dwarf tapeworm of horses – up to 3 cm long

Question 26

Ruminant tapeworms

Answer 26

Moniezia expansa – more in sheep/goats
Moniezia benedeni – more in cattle
> 2 cm long; embryophores triangular - square

Question 27

Pseudophyllidean tapeworms (morphological difference)

Answer 27

Never armed
Only 2 “suckers” – elongate grooves on each side of the
scolex called bothria
Genital pores centrally located
Majority of segments in same stage of development
Egg oval, operculate, yellowish

Question 28

Pseudophyllidean tapeworms (essential life cycle)

Answer 28

Eggs laid in gut – segments shed only when old
**Therefore, eggs found in fecal exams
Hatching eggs requires a light stimulus

Question 29

Diphyllobothrium latum – broadfish tapeworm of man

Answer 29

Hosts: man and other fish-eating mammals
IH I – copepod crustaceans
IH II – most fresh-water fish
Site in FH – small intestine
Morphology – longest known cestode – up to 20 meters; greater than 4000 segments – very fast growing – 1m/3 wks. – produces 7 km of segments over 10 year lifespan
Egg – oval, operculate, yellowish
Importance – In humans, the adult tapeworm withdraws Vit B12 from the intestine and stores it in its tissues – produces pernicious anemia in host

Question 30

Spirometra mansonoides –

Answer 30

Hosts: wild carnivores, dogs, cats
IH I: Water crustacean
IH II: Water snake, frog, rodent, etc.
Importance: Little pathology from adult;
In people, the pleurocercoid causes sparganosis when man serves as IH II. Caused by drinking water containing copepods or by eating raw snakes or tadpoles. Placing poultices of fresh snakes or frogs on open wounds or eyes also infects – painful, inflammation