Microbiology, parasitology & COVID-19

Parasites-gastrointestinal (not liver)

Diphyllobothrium latum

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PubMed Search: Diphyllobothrium latum[TI] cestodes

Haind Fadel, M.D.
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Cite this page: Fadel H. Diphyllobothrium latum. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parasitologydiphyllobothrium.html. Accessed June 7th, 2023.
Definition / general
  • Humans may be infected by one of several species of the fish tapeworm Diphyllobothrium, which normally infect piscivorous mammals and possibly birds
  • Although Diphyllobothrium latum is the most common species to infect humans, differentiation cannot be made based on morphology - molecular methods are required (Emerg Infect Dis 2014;20:1955)
  • Occurs in Northern Hemisphere (Europe, North America, Asia) and South America (Uruguay and Chile)
  • Humans acquire larvae by ingesting raw or incompletely cooked fish that have spent at least part of their life in fresh water
  • Cestode Diphyllobothrium latum (the fish or broad tapeworm) is largest human tapeworm
  • Inhabits small intestine, grows to 10 meters or longer, can persist for years
Diagrams / tables

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Life cycle - Diphyllobothrium latum

Clinical features
  • Adult worms mature and initiate egg production in ~1 month
  • Infection may be asymptomatic, with passage of a length of strobila being the initial complaint (Korean J Parasitol 2007;45:219)
  • In others, a variable degree of abdominal discomfort and diarrhea may be present
  • Rarely, intestinal obstruction occurs
  • In endemic areas in Northern Europe, a small percentage of patients develop vitamin B12 deficiency and associated megaloblastic anemia
  • Diagnosis made by finding the typical brown, oval, operculate eggs in feces using standard recovery techniques
  • Eggs: measure 58 - 76 μm by 40 - 51 μm and in addition to the operculum, have a small round knob-like projection on the abopercular end
  • Scolex: elongated; displays a pair of longitudinal grooves known as bothria, which replace the usual suckers
  • Gravid proglottids: wider than long, have genital pores located midventrally, adjacent to centrally located, rosette shaped uterus
Case reports
  • Praziquantel: adults and children, one dose, 5 - 10 mg/kg orally
  • Niclosamide: adults 2 gm orally once; children 50 mg/kg (maximum 2 gm) orally once
Gross images

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Microscopic (histologic) images

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Eggs in wet mount

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Proglottids and scolex

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Adults and eggs in tissue

Differential diagnosis
  • Other intestinal cestodes
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