Giardia

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.

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

Giardia Flashcards