Giardia

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PARASITES
PROTOZOA



Recognition

Giardia cysts from gerbil faecea - H.D.A. Lindquist, U.S. EPA
Giardia lamblia life cycle - Wikimedia Commons
Giardia lamblia - Janice Carr
Giardia - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
  • Flagellate protozoa
  • Found in the intestine of humans
  • Foundin both wild and domestic animals
  • 15-20μm long
  • Pear-shaped
  • 8 flagella
  • Large adhesive discs to hold onto intestinal mucosa

Life Cycle

  • Simple and direct
  • Trophozoites attach to intestinal wall
  • Reproduce by binary fission
  • Form cysts of 10μm
    • 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 cillous 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-bourne)
  • 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

Diagnosis

  • Faecal examination
    • Cysts need to be distinguished from pollen grains and yeasts
  • Cysts excretion is intermittent
    • Faeces need to be collected over a 3 day period
  • Cysts are heavy
    • Needs higher density floatation fluids
    • Do not float well in saturated sodium chloride solution
  • Immunoassays
    • Detecting cyst antigen in faeces

Control and Treatment

  • Sanitation and hygiene
    • Minimise risk of human infection
  • Boil (or sterilise through other means) drinking water in regions of the world where drinking water may be contmainated
  • Avoid uncooked foodstuffs
    • Contaminated by washing
  • Vaccination
    • Killed trophozoites
    • Availbale in the USA for cats and dogs
    • Decreases the excretion and viability of cysts
    • Decreases environmental pressure