Platyhelminthes pt 2 Digene trematodes and tapeworms

Platyhelminthes pt 2

Digene trematodes and tapeworms

Turbellaria

Monogenea

Trematoda

Cestoda

Cilia lost from ectoderm (parasitic lifestyle)

MicrotrichesScolexProglottids

AcetabulumendoparasiteMollusc/vertebrate life cycle

OpisthaptorEctoparasiteOne host

Free living

Phylum Platyhelminthes

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

Schistosoma mansoni

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

Swimmer’s itch• Schistosoma sp. that infect ducks, muskrat

Blackspot disease: Uvulifer sp.

Fasciola hepatica (sheep liver fluke)F. gigantica (human liver fluke)

Dicrocoelium dendriticum = a bile duct fluke of ruminantssuch as sheep, goats, deer, pigs.

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 marissaschafer@hotmail.com

Turbellaria

Monogenea

Trematoda

Cestoda

Cilia lost from ectoderm (parasitic lifestyle)

MicrotrichesScolexProglottids

AcetabulumendoparasiteMollusc/vertebrate life cycle

OpisthaptorEctoparasiteOne host

Free living

Phylum Platyhelminthes

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

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

Tapeworms

Scolex

Echinococcus granulosis – a tapeworm of dogs & dingoes

Dipylidium caninum

Beef tapeworm: Taenia saginata

Attains a length of 10m

Ligula intestinalis

• Egg → copepod (encycts as a procercoid) → fish (encysts as a plerocercoid larva) → ingested by final host → adult tapeworm in gut of bird