Cestodes & Trematodes Flashcards
Cestodes and Trematodes are in the phylum
Platyhelminths (“flat” “worms”)
Trematode fast facts (3)
-soft, flat bodies
-hermaphroditic
-high reproductive output
Trematodes can also be called
Flukes
2 vet significant liver flukes are
-Fasciola Hepatica
-Fasciola Gigantica
Flukes use ___ as an intermediate host
Snails
Trematodes feed on (3)
-blood
-tissue
-intestinal content
Trematode eggs have a ___ present which is like a ___
Operculum; “trap door” at one end
General Life Cycle of Trematodes (7)
1.Eggs in faeces (or urine/sneezing)
2. Operculum (trap door) of Egg opens when in an aquatic environment and releases Miracidia
3. Miracidia are free living and highly attracted to their specific snail intermediate host (high host specificity)
4. Miracidia burrow through skin of snail and 2-3 generations are produced asexually —> Cercaria
5. Cercaria escape from snail, have a striated tail and move on to infect next host (water plants, fish, crab)
6. When the Cercaria reaches its secondary intermediate host, it encysts to become Metacercaria
7. Definitive Mammal Host ingests secondary intermediate host
When the trematode egg hatches, it releases ___ into water
Miracidium
Factors for transmission of trematodes / flukes include (4)
-presence of intermediate snail host
-presence of suitable secondary intermediate host (usually aquatic plants)
-final host feeding behaviours
-climate
Fasciola (liver flukes) (5)
-large, leaf-shaped
-primarily cattle and sheep but many other species too
-adults live in bile ducts and feed on blood
-Metacircaria found on aquatic plants
-F. Hepatica and F. Gigantica
Life Cycle of Fasciola Hepatica (Liver Fluke) (8)
- Eggs pass into small intestine, excreted with faeces
- Eggs hatch in water to release Miracidium
- Miracidium penetrate snail intermediate host
- Cercaria leave snail and encyst
- Cercaria become Metacercaria
- Metacercaria attach to secondary intermediate host
- Once ingested by definitive host, Metacercaria hatch in small intestine, burrow through lining of duodenum into the body cavity, and migrate until they reach the liver
- Adult worm in bile ducts
Fasciola can cause (4)
-acute liver rot
-secondary disease (Black disease / Clostridium noryi)
-anaemia
-enlargement of liver and bile ducts (Bottle Jaw)
Fasciola is now
Resistant to frontline anthelminthics
Unlike sheep, cattle have ____ to Fasciola
Acquired resistance (calves can get severe disease)
Fasciola is prevalent in
SE QLD and northern QLD, especially dairy farms with green pasture
Minimizing Fasciola transmission to cattle (3)
-rotational grazing
-raised water troughs
-environmental modifications (?)
Paramphistomes (stomach flukes) (6)
-intermediate host is Planorbid snail
-Metacercaria encyst on vegetation
-migrate to rumen and reticulum
-prepatency of 7-13 weeks
-adults are NOT associated with disease (most stock carry light infections)
-heavy infections with IMMATURE can cause damage to intestine, appetite loss, diarrhea
Prepatency is the
Period of time from infection of host to laying eggs
SIMPLE life cycle of Flukes (Trematodes)
Eggs —> Miracidium —> Cercaria —> Metacercaria
Adult Fasciola (liver flukes) live in ___ and feed on ___
Bile ducts; blood
Paramphistomes (stomach flukes) use ___ as an intermediate host
Planorbid snail
Metacercaria of Paramphistomes (stomach flukes) encyst on
Vegetation
Adult Paramphistomes (stomach flukes) are
NOT associated with disease
Heavy infection with ___ Paramphistomes (stomach flukes) can result in
Disease (damage to intestine, appetite loss, diarrhea, etc)
Prepatency of Paramphistomes (stomach flukes) is
7-13 weeks
After ingestion of Paramphistomes (stomach flukes), immature flukes move to
Intestine, then migrate to rumen and reticulum
Cestodes aka ___ are part of the ___ group
Tapeworms; Platyhelminthes
Cestode features include an
Elongated body (strobila) with series of reproductive units (proglottids)
Cestodes lack a ___, instead nutrition is ___
GIT; absorbed across body surface
Transmission of Cestodes occurs via
Passive transfer (relies on predation of host)
With the exception of Spirometra, Cestode eggs
Never hatch in external environment
Two orders of Cestodes are
-Cyclophyllidea (most numerous, attach to mucosa)
-Pseudophyllidea (attach by wrapping around villi)
Taeniidae (Cestode) is the
Adult tapeworm in the GIT of carnivores (ie. dogs, cats, humans)
Taeniidae (Cestode) larvae are called ___ and are always found in
Metacestode; mammal host
Metacestode (larvae) of Taeniidae (Cestodes) are found in
Solid tissues of intermediate host
Tapeworms in the family Taeniidae are distinct in that
The Metacestode (larvae) are ALWAYS found in mammals
Tania saginata (beef tapeworm) life cycle (5)
- Dispersal of proglottids
- Ingestion via Intermediate Host (bovine)
- Metacestode (larvae) found in muscle
- Ingestion of parasite by human via undercooked meat
- Larval scolex attaches to intestinal lining
Three forms of Metacestode (larval stages) of Taeniidae family
-Cysticercus (bladder worm)
-Hydatid Cyst
-Coenurus
Cysticercus (Metacestode of Taeniidae) (4)
-simplest form
-looks like a bladder
-found in solid tissue
-scolex in fluid filled cavity surrounded by membrane
Hydatid Cyst (Metacestode of Taeniia) (4)
-macroscopic cyst
-asexual proliferation of lining gives rise to Brood Capsules
-each Brood Capsules contains up to 12 infective tapeworms called Protoscoleces
-found in liver (eutherian mammals) or lungs (marsupials)
Coenurus (Metacestode of Taenia) (4)
-one scolded within a Brood-like Capsule
-asexual reproduction occurs, but scoleces bud directly from inner lining of cyst
-found in muscle (lagomorphs) and brain of sheep
-causes “gid” or “staggers” in sheep
Taenia infection in definitive host is usually
Sub clinical (ie. does not cause much damage) BUT is a public health concern
Taenia solium (pork tapeworm) always infect ___ and sometimes infect ___
Humans; pigs
Taenia solium (pork tapeworm) life cycle (3)
- Proglottids pass into environment via faeces OR eggs may hatch in GIT and migrate to human brain
- Pigs and humans acquire parasite by eating contaminated food/water
- Pig muscle tissue infected, human gets infected by eating undercooked pork
Which Cestode is only 3 proglottids long
Echinococcus granulosus
Definitive host of Echinococcus granulosus is
Dog, dingo
E. Granulosus Metacestode (larvae) are a
Hydatid cyst
Hydatid cysts of E. granulosus can be either
-fertile (contain live protoscoleces - esp sheep & macropods)
-infertile (protoscoleces never appear - cattle & pigs)
Cysts of E. granulosus have this affect on these species (4)
-Sheep: usually tolerate cysts
-Humans: severe (allergic response, organ enlargement, peritonitis, pneumothorax)
-Eutherian mammals: cysts found in liver
-Marsupials: cysts found in lungs
Transmission of E. granulosus (2)
Intermediate host: infected by ingestion of eggs excreted by dogs
Definitive Host (dogs): eating infected intermediate hosts
Dipylidium caninum (dog or flea tapeworm) relies on
Exposure to fleas to complete it’s life cycle
Clinical significance of Dipylidium caninum
None (owners just get disturbed by seeing proglottids)
Life cycle of Dipylidium caninum (dog/flea tapeworm) (4)
- Flea eats eggs
- Larvae infect flea
- Dog eats fleas
- Adult infects dog in intestine
Common Cestode of grazing animals is
Anoplocephalidae
The invertebrate intermediate host of Anoplocephalidae is usually
Field (orbatid) mites
The Cestode Anoplocephalidae perfoliata will cluster at the ___ and cause ___
Ileocaecal junction; fatal blockage and colic
Common Cestode of sheep is
Moniezia
Spirometra erinacei (zipper worm) < Pseudophyllidea < Cestode life cycle (4)
- Eggs hatch in free water and become Coracidium
- Procercoid burrow into intermediate host
- Intermediate host is eaten by Tadpole (seconda intermediate host) where it becomes Plerocercoid
- Frogs/snakes/rodents eaten by definitive host (cats, dogs, foxes)
Clinical significance of Spirometra erinacei (zipper worm)
Usually none
