Phylum Platyhelminthes, Order Cestoda

Question 1

What is the significance of Cestoda?

Answer 1

Adult stages within the DH is within the SI –> utilise the nutrients and enzymes from the host

The larval stages in the IH are very pathogenic –> located in various tissues but mainly in the liver, brain and lungs. Causes human health concerns and economic losses.

Question 2

What is the morphology of Cestodes?

Answer 2

Segmented body
Can be up to 25m long
Do not have a digestive tract
Located in SI
Hermaphrodites
Contain IH
Adults contain a scolex (head portion - suckers, rostellum with hooks), neck and strobila.
Strobila (body) is made up of immature, mature and gravid proglottids
Immature –> closest to scolex
Mature –> contain both sets of reproductive organs
Gravid –> contain uterus that is filled with eggs.
Proglottids are continuously produced by a process called budding - the neck contains germinal cells.
When the gravid proglottids reach the end of the strobila, they detach and are excreted in the faeces either intact or partially disintegrated.

Question 3

Define Tegument

Answer 3

Tegument - protective coating covering the body

Question 4

Define Parynchyma

Answer 4

Parynchyma - fills the space between the internal organs

Question 5

What is the reproductive system of Cestodes?

Answer 5

All tapeworms are hermaphrodires
Mature proglottids contain one set of female and male reproductive organs

Female reproductive systems - contain ovary, vitelline gland, genital pore
Male reproductive system - testes, genital pore.

Genital pore is where the male and female organs meet within the mature proglottid.

Tapeworms can self fertilise or copulate with another worm.

Within gravids –> contain just uterus and egg, no male reproductive parts

Question 6

What are the features of Cestoda eggs and egg-envolopes?

Answer 6

Within most species of cestodes there is a hexacanth embryo (oncosphere - embryo with 6 hooks)

There are 4 envelopes:

• Capsule (egg shell)
• Outer envelope (vitelline layer)
• Inner envelope (granular layer)
• Oncospheral membrane

Capsules can be thin or thick

Question 7

What are the larval stages within the Order Cyclophyllidea?

Answer 7

Hexacanth embryo - larvae exists within the egg with 3 pairs of hooks

Will develop in the IH as Cysticercus = a bladder enclosing a single invaginated protoscolex (forms into 1 scolex)
Coenurus = a bladder containing many protoscoleces (forms into multiple scoleces)
Hydatid = a bladder with thousands of invaginated protoscoleces which develop within brood capsules (develop into thousands of protoscoleces)

Question 8

What are the larval stages within Order Pseudophyllidea?

Answer 8

1. Coracidium –> hexacanth embryo with cilia (within egg)
2. Procercoid –> solid larca with rounded body and posterior bulb that contains the hooks
3. Plerocercoid –> elongated larvae that can develop into adult tapeworm.

Question 9

What is the medical and veterinary significance of the Family Taeniidae within Order Cyclophyllidea?

Answer 9

DH are represented by carnivorous species only (humans, dogs, cats)

IH = contain many species like humans, ruminants, etc.

Larval stages can develop in various tissues like brain and liver

Humans both IH and DH

Question 10

What are the general features of the Genus Taenia?

Answer 10

Tapeworm are meters long
Made up of hundreds to thousands of proglottids
Scolex contains 4 suckers and rostellum with 2 rows of hooks

Immature proglottids are wider than longer, mature proglottids are square, gracids are longer than wider.
Mature proglottids contain one set of genital organs

Adults located in SI of DH
Larvae can be cysticercus, coenurus and develop in liver / brain, etc.

Eggs not differentiated from Genus Taenia –> hexacanth embryo with 6 hooks, round, brown, embryophore that is striated.

Question 11

What are the general features of Genus Echinococcus?

Answer 11

Milimeters long (very small)
Made up of less than 6 proglottids
Adults located in SI of DH

Larvae contain hydatid only and develops in liver and lungs of IH

Eggs not differentiated from Genus Taenia –> hexacanth embryo with 6 hooks, round, brown, embryophore that is striated.

Question 12

Where are the different larval stages located?

Answer 12

Cysticercis –> located in muscle, liver, peritoneum, eye, brain, etc

Coenurus – brain, spinalcord, Subcut CT

Hydatid –> liver, lungs, heart, spleen, kidney, brain

Question 13

What are the general features of Taenia hydatigena?

Answer 13

adults located in SI
Dog, wolf, fox
Larval stage called Cysticercus tenuicollis –> develops in peritoneum of cattle, sheep, goats and pigs (IH)

Larvae is Cysticercus

Question 14

What are the general features of Taenia pisiformis?

Answer 14

Adults located in SI of dog, wolf, fox (DH)

Larval stage called Cysticercus pisiformis –> develops within liver and peritoneum of rabbits

Larvae is Cysticercus

Question 15

What is the general features of Taenia ovis?

Answer 15

Adults located in SI of the dog, wolf and fox

Larval stage called Cysticercus ovis –> develops in muscle of sheep and goats

Larvae is Cysticercus

Question 16

What is the lifecycle of Taenia spp. (hydatigena, pisiformis, ovis)

Answer 16

Adults within SI
Commonly shed 2-3 gravid proglottids a day
eggs and proglottids found in faeces of infected animals
Egss when shed into the environment are infective immediately for IH

Infection of IH is the ingestion of gravid proglottids / eggs (brown, round, hexacanth, 6 hooks, striated)

IH breaks down eggs and embryo exits –> will penetrate the intestine, migrate to the liver (generally) and develop into mature metacestodes (cysticercus)

Infection of the DH occurs via ingestion of tissues that contain mature metacestodes. Once within the SI of the DH, the protoscoleces evaginate and grow into mature parasites.

Question 17

What are the important Taenia species for humans?

Answer 17

Taenia saginata (larval Cysticercus bovis)
Taenia solium (larval Cysticercus cellulosae)

Question 18

what are the general features of Taenia saginata?

Answer 18

Known as the beef tapeworm
Within the SI of adults (Humans DH)
Larval stage is called Cysticercus bovis –> within cattle (IH)

Cysticercus bovis –> ovid, white vesicles. Commonly found in the heart, tongue, masseter and intercostal muscles

Question 19

What species of Taenia is the larvae Cysticercius bovis found?

Answer 19

Taenia saginata

Question 20

What species of Taenia is the larvar Cysticercus ovis found?

Answer 20

Larvae found in sheep

Taenia ovis –> adults located in carnivorous species (SI)

Question 21

What species of Taenia is the larval Cysticercus pisformis found?

Answer 21

Found in the peritoneum of rabbits

Taenis Pisiformis found in SI of carnivorous species

Question 22

What species of Taenia is the larvae Cysticercus tenuicollis found?

Answer 22

Found within ruminants

Taenia hydatigena is found in SI of carnivorous species.

Question 23

What are the general features of Taenia solium?

Answer 23

Pork tapeworm
Located in the SI of humans (DH)

Larval stage is the Cysticercus cellulosae –> IH is pigs and humans

Humans can be both IH and DH - dependent on the stage of development when infection occurs.

IH of Pigs:
Larvae found in the musculature - heart, tongue, masseter and diaphragm.
White, invaginated scolex with rostellum and hooks.

IH of Humans:
Larvae found in the brain, eye and Subcut CT.

Question 24

What is the Lifecycle of Taenia solium?

Answer 24

Humans infected with parasite will shed hexacanth embryos in the environment (gravid proglottids / eggs)

Eggs can be ingested by pigs –> hexacanth embryo released into the SI of pigs and move to the musculature where they develop into cysticercus. Humans (DH) get infected by eating insufficiently cooked pork that contain cystercerci and the protoscoleces are released and fix to the SI.

Eggs can also be ingested by humans that have poor hygiene –> cystercerci will develop in the brain / eye, etc and will cause severe disease / death (humans as IH)

Question 25

What are the main features of Echinococcus granulosus?

Answer 25

Prevalent in Humans and in Aus
Adults –> smaller (echinococcus are smaller) only contains 6-7 proglottids.
The last proglottid is the only gravid –> but is very long and could be longer than half the length of the worm.
DH is the dog, wolf, dingo, etc (carnivorous canids)
Within the SI (adults)

Eggs are brown, striated, hexacanth embryo with 6 hooks - indistinguishable from Taenia

Hydatid larval stages –> contains a germinal layer with brood capsules (contain protoscoleces) and a laminated layer. The larval stage is surrounded by an adventitial layer. Cyst filled with hydatid fluid.
Can also produce sterile cysts - no protoscoleces

Larval host = humans, located in the liver and lungs (hydatid cysts)

Question 26

What is the lifecycle of Echinococcus granulosus

Answer 26

DH = carnivorous canids
IH = wide range
- Domestic cycle - domestic species
- Sylvatic cycle - wild species

DH shed gravid proglottids / eggs in the faeces
IH (humans, etc) become infected by ingesting hexacanths with food and water

Humans- infected by ingestion of eggs with manipulation of DH (adhere to coats of dogs), ingestion of veggies, plants, etc contaminated with eggs or drinking water contaminated with eggs by the faeces of infected carnivores

After the eggs are ingested, oncosphere hatches in stomach and duodenum. Oncosphere uses hooks to move in the IH and travels to the liver and lungs –> forms small cyst which grows slowly forming hydatid. DH become infected after ingestion of organs containing fertile cysts.

Within DH, protoscolices develop and mature within the SI within 4-6 weeks.

Question 27

What are the main deatures of Echinococcus multilocularis?

Answer 27

DH = foxes 
IH = rodents and humans

Lifecycle is mostly sylvatic –> not present in Australia.

Question 28

What are the general features of Family Anoplocephalidae?

Answer 28

The scolex does not contain rostellum and hooks
Reproductive system are single or double in each segment
Eggs have a pyriform apparatus - wraps around embryo
Insects and mice are IH
Some contain lappets

Question 29

What are the different species of the family Anoplocephalidae?

Answer 29

Anoplocephala perfoliata –> horses
Anoplocephala magna –> horses
Moniezia expansa –> ruminants
Moniezia benedeni –> ruminants

Question 30

What are the main features of Anoplocephala perfoliata?

Answer 30

Scolex contains 4 suckers, 4 lappets, no rostellum, no hooks.

Proglottids are wide and thin (short)
In horses within the ileo-caecal junction

Eggs are D shaped, external envelope is thick, hexacanth embryo is enclosed by large pyriform apparatus.

Question 31

Anoplocephala magna

Answer 31

Infects horses 
No lappets 
No rostellum
No hooks 
Infects horses
Located in SI

Question 32

What is the lifecycle of Anoplocephala spp in horses?

Answer 32

IH = oribatid mites
Horses become infected when mites containing cysticercoid larvae are ingested with the pasture. Cystercercoid larvae are released and grow into adults within the ileo-caecal junction / SI. Gravid proglottids break during passage through horses LI and the EGGS are shed in the faeces.

Eggs are consumed by the mites in the pasture –> cysticercoid larvae fevelop in 2-4 months within in IH –> horses infected after ingestion of mites.

Question 33

What is the general features of the Moniezia species?

Answer 33

Located in Ruminants within the SI
Scolex doesn’t contain rostellum or hooks, proglottids are wider than longer.
Have 2 sets of reproductive organs –> 2 genital pores.

Eggs are triangular in M. expansa, or square in M benedeni
Hexacanth embryo is enclosed by the pyriform apparatus.

Question 34

What is the lifecycle of the Moniezia species?

Answer 34

Similar to Anoplocephala species.
IH = forage mites
Ruminants shed proglottids / eggs in the faeces, eggs ingested by IH , cysticercoid are formed in the body cavity of mites.
DH get infected by ingesting infected mites on the pasture. Moves to the SI where they mature

Question 35

What are the main features of Dipylidium caninum?

Answer 35

Most common tapeworm in dogs
Hosts –> dogs, cats, humans, fox
Located in SI
Rostellum is retractable with more hooks than normal (3-5 rows)
Each proglottid has 2 sets of reproductive organs –> 2 genital pores
Gravid proglottids resemble cucumber seeds with up to 150 egg capsules inside each proglottid.
The embryophore is not striated - contain hexacanth embryo (6 hooks). Within egg capsules.

Question 36

What is the lifecycle of Dipylidium caninum?

Answer 36

IH = flea
Proglottids / eggs pass in faeces or spontaneously out of the anus –> causes puritis and scooting
Eggs are ingested by the larvae of fleas. Cysticercoid larvae develop synchronously with the metamorphis of the flea.
DH ingests adult fleas containing the Cysticercoid larvae.

Question 37

What are the main features of Choanotaenia infundibulum?

Answer 37

Hosts - birds
Located in jejunum
IH = fly

Question 38

What are the main features of Amoebotaenia sphenoides?

Answer 38

Hosts - birds
Located in duodenum
IH = earthworms

Question 39

What are the main features of Davainea proglottina?

Answer 39

Rostellum and suckers provided with hooks
Infects birds
Located in duodenum
Very small
IH = snails and slugs
ingection of the DH is through ingestion of the infected IH

Question 40

What are the main features of Raillietina echinobothrida?

Answer 40

Causes nodules in the intestinal wall 
Rostellum and suckers contain hooks 
infect birds
Located in SI 
IH = ants 
Infection if via ingestion of infected ants

Question 41

What are the general features of the Order Pseudophyllidea?

Answer 41

Known as false tapeworms
Scolex provided with 2 grooves called bothria
Uterus contains an opening –> eggs shed while they are produced
Eggs are operculated and are not developed when laid –> no gravid proglottids
Contain 2 IH in the lifecycle.
No rostellum, no suckers

Eggs released –> develop into coracidium where the operculum opens and the procercoid larvae develops within the 1st IH, the plerocercoid larvae develops within 2nd IH and then moves into the DH within the SI.

Question 42

What are the main features of Spirometra erinacei?

Answer 42

Is a pseudophyllidea
Adults located in SI of dog, cat and fox
Known as the zipper worm as genital pore is obvious
Eggs are yellow, asymmetrical, operculated

Procercoid larvae develop in copepods

Plerocercoid larvae locatedin wide range of hosts (amphibians, reptiles, bird, etc)

Question 43

What is the lifecycle of Spirometra erinacei?

Answer 43

Complex
Uterus has an opening –> operuclated eggs released through uterine pore, exit in faeces into environment

Eggs move into the water, coracidiu forms in egg and hatches –> gets ingested by copepods (1st IH) –> forms into procercoid.

The infected copepods are then ingested by the second IH (any vertebrate except fish) and develops into plerocercoid.

The plerocercoid of the 2nd IH can also be ingested by another vertebrate (PH) but do not mature.

The 2nd IH / PH are ingested by the DH (dogs / cats) –> the plerocercoid larvae develop into adult tapeworms within the SI.

Question 44

What is the significance of Spirometra erinacei?

Answer 44

Human health –> sparganosis

Infection with the plerocercoid larvae in humans cause sparganum

Can be infected by:

• Drinking water that contains copepods infected with procercoid larvae
• Ingesting raw meat from frogs, snakes, birds or mammals containing plerocercoid larvae
• Pressing flesh of infected frog to ulcers, wounds or eyes (Asian practice)