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Platyhelminthes pt 2
Digene trematodes and tapeworms
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Turbellaria
Monogenea
Trematoda
Cestoda
Cilia lost from ectoderm (parasitic lifestyle)
MicrotrichesScolexProglottids
AcetabulumendoparasiteMollusc/vertebrate life cycle
OpisthaptorEctoparasiteOne host
Free living
Phylum Platyhelminthes
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Di(2)-Gene(birth)
• 2 or more hosts• Endoparasitic• No cilia on skin, skin is syncytial • Life cycle:Adults in definitive host (a vertebrate) reproduce
sexually → eggs in host’s feces released into water → hatch into ciliated larva (=miricidium) → snail (intermediate host) → asexual reproduction → sporocyte → redia → cercaria released from snail → metacercaria encysts in 2nd intermediate host (or forage in some cases) → ingested by definitive host
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Schistosoma mansoni
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200 million infected worldwideLeading cause of death of Egyptian men 20-44 years old Adults live in mesenteric veins, veins associated with bladderDamage caused by unegested eggs (50% never released)Control: clean water, sewage control, snail reductionExacerbating factors: poverty & ignorance, dams
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Swimmer’s itch• Schistosoma sp. that infect ducks, muskrat
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Blackspot disease: Uvulifer sp.
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Fasciola hepatica (sheep liver fluke)F. gigantica (human liver fluke)
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Dicrocoelium dendriticum = a bile duct fluke of ruminantssuch as sheep, goats, deer, pigs.
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Tuesday November 13th
CMU Ballroom
Make a team of 3 – 4 students & sign up
on the poster outside SL 118 by
October 16th!!
For more information:
Tri-Beta Meeting October 2nd 6:00 SL118
Chem Club Meeting October 3rd 7:00 HA 405
Or contact Marissa Schafer at [email protected]
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Turbellaria
Monogenea
Trematoda
Cestoda
Cilia lost from ectoderm (parasitic lifestyle)
MicrotrichesScolexProglottids
AcetabulumendoparasiteMollusc/vertebrate life cycle
OpisthaptorEctoparasiteOne host
Free living
Phylum Platyhelminthes
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Class Cestoda - Tapeworms
• Obligate endoparasites of vertebrates
• Lack digestive tract
• Have scolex for attachment to host
• Body divided into proglottids– Each proglottid = egg factory with its own
ovary and testis (make up to 50,000 eggs per proglottid)
– Worm = hundreds to thousands of proglottids
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General life cycle of tapeworms
• Adult in intestine of definitive host → proglottids break off and pass with feces → eggs released from proglottid → eaten by intermediate host → oncosphere larva → intermed host ingested by definitive host → adult develops in intestine
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Tapeworms
Scolex
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Echinococcus granulosis – a tapeworm of dogs & dingoes
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Dipylidium caninum
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Beef tapeworm: Taenia saginata
Attains a length of 10m
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Ligula intestinalis
• Egg → copepod (encycts as a procercoid) → fish (encysts as a plerocercoid larva) → ingested by final host → adult tapeworm in gut of bird