Parasitology: Cestodes

Front 1

What are the physical characteristics of tapeworms in general?

Back 1

Tapeworms consist of a chain (strobila) of progessively maturing, independent reproductive units (segments or proglottids) anchored at one end to the intestinal wall by an anchor organ (scolex).

Front 2

Pseudophyllideans

Back 2

Scolex with four longitudinal grooves.
Central genital pre on each segment.
Eggs and lifecyles bear some similarity to trematodes
Subtropical: Spirometra

Front 3

General characteristics of Cyclophyllideans

Back 3

Scolex with four circular suckers
Some with ‘hooks’  “armed”
Most live in small intestine
New segments bud off
Each segment develops male and female organs  INDEPENDENT
Cross fertilize
LATERAL genital pores
“Gravid” segments may contain >100,000 eggs

Front 4

Segments of Cyclophyllideans

Back 4

1 or 2 segments drop off daily and exit the animal
Mobile, and also excreted with feces
LATERAL! Genital pore

Front 5

Eggs of Cyclophyllideans

Back 5

A tapeworm larvae with six hooks (onchosphere) surrounded by a ‘shell’ made of numerous blocks

Front 6

Life cycle of Cyclophyllideans

Back 6

Adult tapes in final host  shed segments/eggs  eggs in environment  swallowed  onchosphere travels in blood stream to predilection site  larval tapes develop (metacestodes)  Intermediate host tissue eaten  metacestode swallowed  new infection in final host

Front 7

What are metacestodes?

Back 7

The larval stage of tapeworms.

Front 8

What are the 6 types of metacestodes?

Back 8

Cysticercus: a fluid filled bladder with one inverted scolex.
Cysticercoid: invertebrates only; reduced bladder.
Coernus: like a cysticercus but has multiple inverted scolices.
Strobilocercus: cat tapeworm Taenia taeniaeformis; like a cysticercus but single scolex is attached to a bladder by a chain of segments.

Front 9

Hydatid cyst

Back 9

fluid filled bladder
Inverted solices
Hydatid fluid and hydatid sand, usually walled off by fibrous tissue

Front 10

Alveolar cyst

Back 10

Similar to hydatid cyst but daughter cysts bud off the external surface and the cyst expands by infiltrating through tissue like a tumor

Front 11

Echinococcus

Back 11

Taeniid tapeworm
Important zoonosis
Hydatid cyst can develop in humans as well as in many other animals
Can grow to ping pong size in sheep, tennis ball in horse, and a soccer ball in man.

Front 12

Life cycle of Echinococcus granulosus

Back 12

Final host is dog, fox, or other canid
Small worm 0.5cm long
Scolex is deeply burried in intestinal crypt
PPP 6 weeks
1 gravid segment passed each week
LOW biotic potential
Intermediate host infected by ingesting eggs
Half the size of a ‘strongyle egg’
Metacestode is a hydatid cyst

Front 13

Echinococcus multiocularis

Back 13

Final host is fox
Simlar to E. granulosus, however:
Metacestode is a alveolar (or mutilocular) cyst
Particularly dangerous as invades tissues by ‘budding off’ externally
Ie: will infiltrate the liver like an invasive tumor and be inoperable

Front 14

Taenia saginata:
Final host, intermediate host, metacestode?

Back 14

Final host: human
Intermediate host: cattle
Metacestode: cysticercus in muscle

Front 15

Taenia solium:
Final host, intermediate host, metacestode?

Back 15

Final host: human
Intermediate host: pig
Metacestode: cysticercus in muscle

Front 16

Taenia ovis:
Final host, intermediate host, metacestode?

Back 16

Final host: dog
Intermediate host: sheep
Metacestode: cysticercus in muscle

Front 17

Taenia hydatigena:
Final host, intermediate host, metacestode?

Back 17

Final host: dog
Intermediate host: sheep and other ruminants
Metacestode: cysticercus in peritoneum

Front 18

Taenia pisiformis:
Final host, intermediate host, metacestode?

Back 18

Final host: dog
Intermediate host: rabbit
Metacestode: cysticercus in peritoneum

Front 19

Taenia multiceps:
Final host, intermediate host, metacestode?

Back 19

Final host: dog
Intermediate host: sheep, rabbit
Metacestode: coernus in skull

Front 20

Taenia serialis:
Final host, intermediate host, metacestode?

Back 20

Final host: dog
Intermediate host: sheep, rabbit
Metacestode: coernus in inter-muscular connective tissue.

Front 21

Taenia taeniaeformis:
Final host, intermediate host, metacestode?

Back 21

Final host: cat
Intermediate host: mice, rodents
Metacestode: strobilocercus in liver

Front 22

How are humans infected by T. saginata?

Back 22

By eating undercooked beef.

Front 23

Is T. saginata armed?

Back 23

No, the scolex does not contain any hooks.

Front 24

How are cattle infected with T. saginata?

Back 24

By ingesting eggs on pasture or through a contaminated environment.

Front 25

Direct transmission of T. saginata.

Back 25

Eggs reach pasture by direct deposition of human feces
RARE in developed nations

Front 26

Indirect transmission of T. saginata

Back 26

sewage, sludge on agricultural land
Birds: serve as a transport mechanism for whole proglottids

Front 27

Epidemiology of T. saginata

Back 27

May be found in any straited muscle but highest in density are heart, tongue, and masseters
Cuts are made in these during meat inspection

Front 28

Enzootic instability

Back 28

Good sanitation, very low prevalence in human population  low transmission rates to cattle  low prevalence in cattle  sporadic ‘storms’ of infection

Front 29

Enzootic stability

Back 29

High prevalence in humans due to lack of sanitation  high rate of transmission to cattle  many calves infected  calves infected, but animal immune to reinfection

Front 30

Is T. solium armed?

Back 30

Yes, it has hooks on its scolex.

Front 31

Life cycle of T. solium

Back 31

Similar to T. saginata except pig is the intermediate host.

Front 32

What part of the body of pigs and humans does T. solium infect?

Back 32

The brain and musculature.

Front 33

General characteristics of Taenia spp. in dogs.

Back 33

Adults live in small intestine and appear to cause little harm, although exiting proglottids may cause pruritis
Main issue is in intermediat hosts: ie sheep
PPP 6-8 weeks
Taenia segments ≠ Dipylidium!!!
Are rectangular
Only one lateral genital pore
Eggs are single, not in packets like dipylidium

Front 34

Life cycle of T. hydatigena

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Oncospheres  hepatic portal system  transform to cysticerci  grow rapidly while migrating through liver parenchyma  PERITONEAL cavity

Front 35

How does T. hydatigena hurt/damage sheep?

Back 35

Damages liver, and liver heals forming fibrous tracts  condemnation at meat inspection
Can cause massive liver damage and death

Front 36

Life cycle of T. multiceps (aka Multiceps multiceps)

Back 36

Eggs hatch in SI of sheep
Onchosphere  blood circulation  brain  migrates through brain tissue  coernus inside skull lying on surface of brain

Front 37

Neurological signs of T. multiceps in sheep?

Back 37

ataxia, circling, blindness

Front 38

General info on T. ovis

Back 38

Similar cycle to T. hydatigena
Cysticerci occur in MUSCULATURE
Condemnation of meat on aesthetic grounds

Front 39

General info on T. pisiformis

Back 39

Similar to T. hydatigena, except cysticerci are pea sized and found on omentum of rabbits

Front 40

General info on T. serialis

Back 40

Coernus forms in intermuscular connective tissue of rabbits
Pet rabbit probably get it from wild foxes

Front 41

General info on T. taeniaeformis

Back 41

CAT Taenia
Pea sized nodule metacestode found in liver of mice and other small rodents
Cats can continue to be reinfected (hunters)

Front 42

General characteristics of Dipylidium caninum

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Very common in cats and dogs.
Minor clinical sign: anal irritation.
Recognition: Segments are oval in shape
Two lateral genital pores
Clusters of eggs in packets

Front 43

Dipylidium caninum lifecycle

Back 43

When ingested by flea larvae  onchosphere transforms to a cysticercoid which is infectie  flea is swallowed during grooming

Front 44

General info on Anoplocephala spp.

Back 44

Intermediate host are free-living pasture mites
Mestacestode is a cysticercoid
Horses become infected when grazing

Front 45

General info on Moniezia spp.

Back 45

Intermediate host are pasture mites
Sheep and cattle (mostly lambs)

Front 46

General info on Davainea spp

Back 46

Poultry tapeworm
Intermediate host are: earthworms, beetle, mollusk, insect, etc

Front 47

General info on Spirometra spp.

Back 47

Pseudophyllidean
Several spp
Dogs and cats are final hosts
Aquatic copepods are the first intermediate host, and vertebrates such as frogs, snakes, rodents are second intermediate hosts
Humans can be infected
Sparganosis

Front 48

What is the treatment for tapeworms?

Back 48

Praziquantel