Giardia

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

Giardia cyst - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

• Flagellate protozoa

• Found in the intestine of humans

• Associated with chronic diarrhoea

• Found in both wild and domestic animals

• 15-20μm long

• Pear-shaped

• 8 flagella
  • 6 flagellae are free

• 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
  • 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 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

• Drug Treatments
  • Metronidazole
    • Flagyl, Torgyl
  • Fenbendazole
    • Panacur

• Vaccination
  • Killed trophozoites
  • Availbale in the USA for cats and dogs
  • Decreases the excretion and viability of cysts
  • Decreases environmental pressure