From WikiVet English
Jump to navigation Jump to search
Kingdom Protista
Sub-kingdom Biciliata
Phylum Metamonada
Super-class Eopharyngea
Class Trepomonadea
Sub-class Diplozoa
Order Giardiida
Family Diplomonadidae
Genus Giardia
Giardia lamblia life cycle - Wikimedia Commons
Giardia lamblia - Janice Carr
Giardia - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Giardia cyst - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine


These protozoan parasite are found in humans as well as wild and domestic animals. They are a common cause of severe diarrhoea as part of the clinical symptoms giardiasis.


Giardia spp. are flagellate protozoa with 8 flagella, 6 of which emerge from the body and are used in motility. They are 15-20μm long, pear shaped with a flat ventral surface. The most unique feature of this protozoa is the presence of a large adhesive disk in the flat surface that is used for attaching to the intestinal mucosa.

Life Cycle

  • Simple and direct
  • Trophozoites attach to intestinal wall
  • Reproduce by binary fission
  • Form cysts of 10μm
    • Multi-nucleate cysts formed intermittently
    • Immediately infective when passed in faeces
  • Prepatent period of 5-6 days


  • Commonest cause of protozoal diarrhoea of man in the UK
  • Common in domesticated animals
  • Infections often asymptomatic in domestic animals
    • Can cause villous atrophy leading to malabsorption
    • Infection can persist for weeks to months if not treated


  • Infection via direct oral-faecal route or through contaminated water source (water-borne)
  • Wild animals may act as a source of infection for humans
    • E.g. Beavers
  • Divided into 7 species
    • G. duodenalis most commonly infects humans
      • Some subspecies are zoonotic

Giardia Learning Resources
VetstreamVetlexicon advert button.png
To reach the Vetstream content, please select
Canis, Felis, Lapis or Equis
FlashcardsFlashcards logo.png
Test your knowledge using flashcard type questions
Giardia Flashcards