Giardia

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Giardia
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

Overview

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.

Recognition

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

Pathogenesis

  • 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

Epidemiology

  • 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


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