[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/) › Dibothriocephalus latus

[Microbiology](https://durgical.com/en/microbiology/) · [Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/)

# Dibothriocephalus latus

- Parasite
- For completeness

The longest human tapeworm; it comes from raw or undercooked fish. It can steal vitamin B12 and cause megaloblastic anaemia.

Updated 2026-11-01

Also called: Diphyllobothrium latum (former name), fish tapeworm, broad tapeworm

## Key points

- Raw fish → the longest human tapeworm.
- Vitamin B12 deficiency and megaloblastic anaemia.
- Operculated egg with an opposite knob.
- Scolex with bothria, no suckers or hooks.
- Current name: Dibothriocephalus latus.

## At a glance

**Shape**
Elongated scolex with two grooves (bothria), no suckers or hooks

**Family**
Diphyllobothriidae

**Type**
Cestode (diphyllobothriid), fish tapeworm

**Size**
Adult can exceed 10 m

## Morphology

- Proglottids broader than long, with a rosette-shaped uterus and one ventral genital pore.
- Operculated egg, 55–75 × 40–50 µm, with a small knob at the opposite end.
- Eggs are passed unembryonated and are usually abundant.

## Transmission

- Eating raw, marinated or undercooked fish with plerocercoid larvae.
- Raw fish dishes (ceviche, sushi) made with fish that was not frozen.

**Reservoir:** Humans; Bears and other fish-eating mammals; Freshwater and some marine fish

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Life cycle

- Operculated eggs leave in stool and mature in water.
- The hatched coracidium is eaten by a small crustacean (copepod), where it forms the procercoid.
- A small fish eats the crustacean; the larva moves into its flesh as an infective plerocercoid.
- Larger predatory fish accumulate plerocercoids by eating the small ones.
- A person eats raw or undercooked fish; the adult grows in the bowel and lays eggs in 5–6 weeks.

## Virulence factors

- The worm absorbs vitamin B12 in the small bowel and competes with the host.
- Prolonged deficiency can cause megaloblastic anaemia and neurological symptoms.
- Most infections are mild; rarely obstruction or cholangitis.

## Diseases it causes

- Intestinal diphyllobothriasis, usually mild
- Megaloblastic anaemia from vitamin B12 deficiency (uncommon) [Megaloblastic anaemia (B12 or folate deficiency) →](https://durgical.com/en/conditions/megaloblastic-anaemia/)

## Clinical picture

- Asymptomatic or with mild GI complaints.
- Passing chains of proglottids.
- Pallor, glossitis and paraesthesia if B12 is deficient.

## Diagnosis

- Abundant operculated eggs on stool microscopy, visible without concentration.
- Broad proglottids in stool.
- Blood count and vitamin B12 levels.
- PCR to identify the species, mainly in research.

## Treatment

Cestocides: praziquantel (drug of choice) or niclosamide; vitamin B12 replacement if deficient.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Praziquantel](https://durgical.com/en/pharmacology/praziquantel/)

## Prevention

- Cook fish, or freeze it properly before eating it raw.
- Sanitation so that human faeces do not reach rivers and lakes.

## Memory aid

Raw fish, stolen B12: the fish tapeworm eats your vitamin before you do.

## Test yourself

Think of the answer, then tap the question to see it.

## Which vitamin deficiency can the fish tapeworm cause?

Vitamin B12 deficiency, with megaloblastic anaemia.

## What does the Dibothriocephalus latus egg look like?

Operculated, 55–75 µm, with a small knob at the end opposite the operculum.

## How is diphyllobothriasis acquired?

By eating raw, marinated or undercooked fish containing plerocercoid larvae.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/dibothriocephalus-latus/)

## Related

- [Taenia saginata](https://durgical.com/en/microbiology/taenia-saginata/)
- [Hymenolepis nana](https://durgical.com/en/microbiology/hymenolepis-nana/)

## Related conditions

- [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Cestodes (tapeworms)](https://durgical.com/en/microbiology/groups/cestodes/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [CDC - DPDx - Diphyllobothriasis](https://www.cdc.gov/dpdx/diphyllobothriasis/index.html) (CDC, 2019); [Fish tapeworm infection: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001375.htm) (MedlinePlus (NLM), 2025).

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Representative model, for educational purposes only.

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