Cestodes: Diphyllobothrium latum (Broad/Fish Tapeworm Life Cycle)

Diphyllobothrium latum: Broad tapeworm or Fish tapeworm

• Largest human tapeworm

– Grows up to ten meters long

• Life cycle includes two intermediate hosts:

– Early larval forms are ingested by microcrustaceans, which are then eaten by fish. – When humans eat undercooked infected fish, they become the definitive hosts.

• Serious infection can cause Vitamin B12 deficiency, pernicious anemia, and intestinal obstruction.

1. Eggs release ciliated coracidia. 2. Coracidia are ingested by copepods (microcrustaceans) - these are the first intermediate hosts. 3. In the copepods. Coracidia develop into procercoid larvae. 4. The copepod & procercoid larvae are ingested by fish - fish are the second intermediate host. 5. In fish, procercoid develops into plerocercoid larvae (aka, sparganum). 6. Humans eat infected fish (usually larger fish who ate the smaller infected fish) 7. In humans, the plerocercoid develop into adults that live in small intestine and release eggs. – Adult scolex has a pair of linear sucking grooves (not hooks or suckers), and rosette-shaped uteruses with pores that pass eggs to the outside (segments don't break off like Taenia). – Adults release up to a million eggs/day/worm. 8. Eggs are released in the feces. https://www.cdc.gov/dpdx/diphyllobothriasis/index.html