Parasite
Diphyllobothrium latum
Fish tapeworm linked to B12 deficiency
dye-fil-oh-BOTH-ree-um LAY-tum
High-yield clue
Raw freshwater fish transmission and vitamin B12 competition causing megaloblastic anemia are the defining clues.
Overview
The broad fish tapeworm, now accepted as Dibothriocephalus latus (older name Diphyllobothrium latum), the largest human tapeworm, acquired from raw or undercooked freshwater fish and famous for competing with the host for vitamin B12.
Classification
- Cestode (tapeworm)
- Current name Dibothriocephalus latus (2017 revision)
- Largest human tapeworm
- Copepod first host, freshwater fish second host
- Operculated eggs
Lab & identification clues
- Operculated eggs on stool examination
- Proglottids wider than long vocabulary
- Eggs distinguish it from Taenia
Associations
- Raw/undercooked freshwater fish (e.g., pike, perch)
- Vitamin B12 deficiency and megaloblastic anemia
- Cold-lake and pickled-fish epidemiology
- Often asymptomatic carriage
Commonly confused with
- Taenia species
- Clonorchis sinensis
Frequently asked questions
What is Diphyllobothrium latum?
The broad fish tapeworm, now accepted as Dibothriocephalus latus (older name Diphyllobothrium latum), the largest human tapeworm, acquired from raw or undercooked freshwater fish and famous for competing with the host for vitamin B12.
What are the lab clues for Diphyllobothrium latum?
Lab clues for Diphyllobothrium latum include Operculated eggs on stool examination, Proglottids wider than long vocabulary, and Eggs distinguish it from Taenia.
What is Diphyllobothrium latum commonly confused with?
Diphyllobothrium latum is commonly confused with Taenia species and Clonorchis sinensis.
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.