cestoda I (tapeworms)

cestode body composition

• scolex - head

  • may be armed with spines

• neck - regenerative region; continuously generates proglottids

• strobila - segmented part of the body

  • proglottid - individual segment

  • note: each proglottid has its own reproductive capacity

cestode infection site

intestines (adult in definitive host; larval forms can go to a variety of locations)

cestode general characteristics

• no digestive system; feed through “tegument” (selective uptake of nutrients)

• hermaphroditic

immature proglottid

does not contain any sexual organs

mature proglottid

contains male and female sex organs

gravid proglottid

• mature and can produce eggs

• each has male and female portion

genital pore

• common external opening of male & female reproductive system

• can be lateral, medial, or bilateral depending on species

metacestode

• cestode larval stage

• lives within intermediate host

• infection site: body tissues/cavities

  • species-dependent migration

• variety of different morphologies, depending on species

  • each tapeworm species follows one developmental pathway

• major source of pathology!

oncosphere

• thick-shelled egg containing hexacanth larva

  • hexacanth → 6 hooks (3 pairs)

plerocercoid

• metacestode that infects fish/frogs (aquatic, cold-blooded vertebrates)

  • can also infect mammals, including humans

• poorly defined suckers, unarmed, nondescript

cysticercoid

metacestode that infects arthropod intermediate host (ex. fleas, beetles)

cysticercus

• metacestode that infects mammalian intermediate host (can include humans)

• fluid filled sac with scolex in center → “bladder worms”

hydatid cyst

• metacestode that infects mammalian intermediate host (can include humans)

• filled with fluid

• many scolices in each cyst

• can asexually reproduce

cestodiases pathology

• adults in definitive host

  • generally little pathology; commonly asymptomatic

  • heavy infections: GI pain/discomfort, diarrhea, constipation, disruption of proper digestion/nutrition

• metacestodes in intermediate host

  • major source of pathology

  • varies with intensity and tissue location

  • economic importance → production loss, condemnation of meat

cestodiases diagnostics

• adult

  • definitive diagnosis: eggs/proglottids in feces

  • history/clinical signs

• larvae

  • clinical signs, serology, imaging

  • visual ID at surgery, necropsy, or slaughter

cestodiases treatment

• anthlemintics - available adulticides

  • praziquantel, epsiprantel, niclosamide

• albendazole → larvacide

• treat definitive hosts to stop transmission

• avoid contact/ingestion of intermediate hosts

cyclophyllidea

• terrestrial cestodes

• distinct suckers around scolex

• taenia, echinococcus, dipylidium, mesocestoides, moniezia, anoplocephala

pseudophyllidea

• aquatic cestodes

• poorly defined suckers on scolex

• diphyllobothrium, spirometra

cyclophyllidea general life cycle

oncosphere eggs/proglottids passed in feces → eggs ingested by intermediate host → develop to metacestode stage (cysticercoid, cysticercus, or hydatid cyst) → infected intermediate host ingested by definitive host → adult worms in GI of definitive host

pseudophyllidea general life cycle

coracidium (ciliated oncosphere egg) passed in feces → hatch/ingested by 1st intermediate host (copepod) → metacestode infects 2nd intermediate host (plerocercoid - fish/frog or spargana - mammal) → 2nd intermediate host ingested by definitive host → adults in GI tract of definitive host

diphyllobothrium definitive hosts

dog, cat, human

diphyllobothrium intermediate hosts (2)

• 1st = copepod (ex. plankton)

• 2nd = fish (ex. perch, walleye)

  • plerocercoid

diphyllobothrium diagnostic stage

• eggs in feces

• similar in appearance to trematode eggs

• operculated

spirometra definitive hosts

dog, cat

spirometra intermediate hosts

• 1st = copepod

• 2nd:

  • frogs (plerocercoid)

  • rodents, dogs, humans, etc. (spargana)

spirometra diagnostic stage

eggs in feces; more likely to float than diphyllobothrium

pseudophyllidean cestodiases pathology

• adults (in definitive host)

  • little pathology unless numerous

    • GI disturbance (diphyllobothrium, spirometra)

    • anemia due to B12-deficiency (diphyllobothrium; specific strain in Great Lakes)

• metacestodes (in intermediate host)

  • infection by spirometra plerocercoid → sparganosis (serious!)