Section 2: cestodes (life cycles)

Diphyllobothrium life cycle

1. unembryonated eggs passed in feces

• eggs find way to water

2. eggs embryonate in water

• coracidia hatch from eggs

3. coracidia ingested by crustaceans (1st intermediate host)

4. procercoid larvae develop in crustaceans body

• infected crustacean eaten by small fish (2nd intermediate host)

5. procercoid develop into pleurocercoid in fish (infective stage)

6. predator fish eats small infected fish that have pleurocercoid

• invade tissue, not developing

• paratenic host (optional)

7. ingest raw/undercooked infected fish (humans; definitive host)

• pleurocercoids uses scolex to attach to small intestine

• develop into adult

8. adult in small intestine

9. proglottids release unembryonated eggs

10. unembryonated eggs passed in feces

Taenia pisiformis life cycle

1. eggs or gravid proglottids are passed in feces

2. cattle/pigs become infected by ingesting vegetation infected by eggs or gravid proglottids

• oncospheres hatch from eggs

• oncospheres penetrate intestinal wall

3. oncosphere develop into cysticerci in muscle

4. ingest raw or undercooked meat (human)

5. scolex attaches to lining of small intestine

6. adults in small intestine

7. eggs or gravid proglottid passed in feces

Echniococcus granulosus life cycle

1. adult in small intestine

• in definitive host (god)

2. embryonated eggs in feces

• humans can become infected (have to have adult form)

  • cyst from dog, ingested

    • oncospheres released

    • cysts in various organs (lungs/brain/liver)

3. oncospheres hatch

• penetrate intestinal wall

• invade various organs to form tissue cysts

4. hydatid cysts

• in liver, brain, lungs

• ingested by intermediate host through feces

  • definitive host (dog) can become infected in it eats infected sheep

• potential adult worm in cyst

5. protoscolex comes out of cyst

6. scolex attaches to intestine

• develops into aduly

7. adult in small intestine

Dipylidium caninum life cycle

1. gravid proglottids passed in feces

• emerge from perianal region

• eggs intact when discreated

2. proglottids disintegrate

• release egg packets

3. larva of flea ingest egg packets

• oncospheres hatch and develop into cysticercoids

4. flea larva mature into adult fleas

• harbor cysticercoids

5. definitive host infected

• ingesting fleas (usually dogs/cats)

  • reach small intestine and become adult

• can infect human

  • dog/cat

    • can harbor fleas infective to humans

  • can ingest infected flea directly

  • adult in small intestine

6. gravid proglottids passed in feces/emerge from perianal region