Cestodes Flashcards
Cestode morphology
Flat, solid-bodied and segmented, with a scolex, neck, and strobila; they lack a digestive tract
What type of life cycle do cestodes have?
Indirect life cycles with at least 1 intermediate host
Describe the sexuality of cestodes
Hermaphrodites - sexual +/- asexual reproduction (depends on the larval stage)
How do Cyclophyllideans differ from Pseudophyllideans?
What is a metacestode?
The larval stage of cestodes
Describe the differences between the various metacestode stages of cyclophyllideans
Within a hydatid cyst, what can you find many of?
Endogenous cysts
Describe Dipylidium caninum (cucumber seed tapeworm)
- DH: canids, felids, humans - ZOONOTIC
- Habitat: SI
- Morph:
- Adults - up to 50 cm long, armed scolex, 4 suckers, bilateral genital pores
- Egg packets contain multiple eggs, each 45 um—> hexacanth embryo
Describe the Dipylidium life cycle
- Gravid proglottids break off in SI, are passed in feces or actively crawl out
- Proglottids rupture, release egg packets
- Eggs ingested by IH
- Larval fleas
- Chewing louse of dogs
- Eggs develop into infective cysticercoid
- IH ingested by DH (dog, cat, human)
- Scolex attaches to SI, grows
- Self- or cross-fertilization occurs
- PPP = 2-3 weeks
Describe the disease caused by Dipylidium caninum
- Usually non-pathogenic
- typically “scooting across the floor”
Describe Taeniid tapeworms
- Large worms
- are armed - rostellum with double row of small + large hooks
- have proglottids longer than they are wide
- have single genital pore per proglottids (irregularly alternating)
- have characteristic taeniid-type egg
- embyrophore is brown and radially striated
- Hexacanth embryo with 6 hooklets
- live in SI as adults
- are more pathogenic as metacestode than as adults
Describe the general Taeniid life cycle
- Adult tapeworms attached to SI
- Gravid proglottids pass in feces or migrate out
- rupture releases eggs
- IH ingests egg —> oncosphere hatches, penetrates SI mucosa —>enters circulation
- Metacestode develops in various organs/tissues
- DH ingests IH
- Scolex released, attaches to SI and grows
Describe Taeniid taeniaeformis
- DH: cats, other felids
- IH: Rats, mice, other small rodents —> liver
- Morph:
- Adults - 60 cm long, armed, 4 suckers
- Strobilocercus
- Disease: Heavy infection — obstruction reported
What are these?
T. Taenoiaformis eggs
What is this parasite?
T. Taeniaformis strobilicercus in liver
Describe Taeniid pisiformis (rabbit tapeworm)
- DH: Dogs
- IH: rabbits, hares, occasionally rodents - peritoneal cavities
- Morph:
- Adults: 200 cm long, armed, 4 suckers
- Cysticercus = pea sized
- Disease: Heavy infection - constipation, ill thrift, pot-belly
Describe Taenia ovis (mutton tapeworm)
- DH: Dogs
- IH: Sheep, goats — skeletal and cardiac muscle
- Morph:
- Adults 100-200 cm, armed, 4 suckers
- Taenid eggs
- Cysticercus
- Disease: Heavy infection - constipation, pot belly, diarrhea
Taenia hydatigena (ruminant tapeworm)
- DH: Dogs
- IH: sheep, goats, sometimes pigs - peritoneal cavity
- Morph:
- Adults 75-100 cm long, armed, 4 suckers
- Taenid eggs
- Cysticercus
- Disease: Heavy infection - constipation, diarrhea, pot-belly
Describe Taenia multiceps (sheep coenurus worm, gip)
- DH: dogs, foxes, coyotes
- IH: sheep, goats - brain, spinal cord
- Morph:
- Adults 40-100 cm long, armed, 4 suckers
- Coenurus
- Disease: heavy infection - constipation, diarrhea, pot belly
Taenia serialis (rabbit coenurus tapeworm)
- DH: Dogs, foxes, coyotes
- IH: Rabbits - SC and IM connective tissues
- Morph:
- Coenurus - Scolices lined up in rows (‘serialis)
- Disease: same as other Taenids
Echinococcus granulosus
- Distribution: Northcentral, midwestern and southwestern US
- DH: Dogs, carnivores
- IH: cattle, sheep, sometimes horses, pigs, humans
- liver, lung, brain
-
Morph:
- Adults 4-7 mm long (very tiny), armed, 4 suckers, 3-4 proglottids
- Unilocular hydatid cyst
What are you looking at?
Echinococcus granulosus (adult)
WHAT ARE THOSE
Echinococcus granulosus hydatid cysts in liver and lung
What are these?
Enterococcus granulosus protoscolex
Inverted (left)
Everted (right)
Describe Entercoccus multilocularis
- Distribution: northern US
- DH: dogs, cats, foxes
- IH: dogs, rodents, humans — liver, lung
- Morph:
- Adults: 1-5 mm, 2-6 proglottids
-
Multilocular hydatid cysts, size depends on locaiton
- Budding daughter cysts infiltrate tissue like malignant tumor
-
Disease:
- DH: usually harmless, can harbor thousands of adults
- IH: domestic animals typically asymptomatic, humans - organ dysfunction
WHAT ARE THOSE
(Enterococcus multilocularis) multilocular hydatid cyst
What are these lesions associated with?
Enterococcus multilocularis
Why should you treat both Taenia and Echinococcus from wild canids with caution?
Because these species have indistinguishable eggs and Echinococcus eggs have zoonotic potential
Describe Spirometra mansonoides (zipper tapeworm)
- DIstribution: Southern US, down into S. America
- DH: Cats, dogs, raccoons
- Habitat: SI
- IH: copepod (1st), frog/snake/rodent/fish (2nd)
-
Morph:
- Adults up to 1.5 m long, bothria, medial uterine pore
- Eggs light brown, operculated
Describe the life cycle of Pseudophyllidean tapeworms
- Adults in SI produce operculated eggs —> shed into feces
- Upon contact with water —> coracidium develops and emerges
- Copepod 1st IH ingests coracidium -> develops into procercoid in body cavity
- Vertebrate 2nd IH (frog, rat, snake) ingests copepod
- procercoid migrates to muscle, CT —> develops into plerocercoid/sparganum —> encysts
- DH ingests 2nd IH —> plerocercoid attaches to SI and grows
- PPP: 10-30 days
Describe the disease caused by Pseudophyllideans
- Adult stages usually non-pathogenic
- may cause V/D, weight loss
- Larval tapeworms: Sparganosis
- Dogs, cats, humans (zoonosis)
- Infected via ingestion of 1st or 2nd IH, or use of 2nd IH as poultice on wound
- Signs depend on final location of migrating sparganum (e.g. lungs, CNS)
- Proliferative form rarely reported
What parasite caused these lesions?
Spirometra mansonoides (Sparganosis); this was a pneumothorax
Describe Diphyllobothrium spp. (Broad fish tapeworm)
- Distribution: worldwide
- DH: humans (primary), cats, dogs, bears, fish-eating mammals
- IH: copepod (1st), fish (2nd)
- Habitat: SI
- Morph: Long adults with medial uterine pore and bothria w/ operculated egg
- Disease:
- Vomiting, diarrhea, wt loss
- Zooanthroponosis: abd discomfort, weakness, nausea; pernicious anemia (B12 deficiency)
How does the Diphyllobothrium lifecycle differ from that of Spirometra?
- The second IH = freshwater fish
- in dogs: PPP = 3-4 weeks
How do you diagnose Taenia and Dipylidium?
- Proglottids: in the feces, bedding, and perianal area, longer than the are wide
- +/- eggs in fecal float
How do you diagnose Echinococcus?
- Proglottids are too small to notice
- Eggs seen in fecal float, can also use coproantigen ELISA
How do you diagnose Pseudophyllideans?
- Proglottids in the vomitus or feces; wider than they are long
- Eggs found in fecal float, can also do fecal sedimentation
What is the only method of differentiating Taenid and Echinococcus eggs?
PCR
How do you diagnose cestodes grossly?
- You can break open proglottids and examine for eggs
- you can ID adult worms using their scolices
- if you necropsy the IH, you can ID the metacestodes
What are the treatments for Pseudophyllideans?
Praziquantel (extra-label)
What is the treatment for Cyclophyllideans?
- Praziquantel - only product approved for Echinococcus spp.
- Epsiprantel
- Fenbendazole - Taenia spp. Only
How do you prevent cestode infestation?
- Prevent predation and scavenging
- do not feed raw/undercooked meat or fish
- Flea control
- For pets with at-risk lifestyle, regular fecal monitoring and anthelmintic tx is recommended
- Pets in Echinococcus-endemic areas should receive monthly praziquantel
