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Giardia Lamblia

Epidemiology of Infectious Diseases: Giardia Lamblia

Causal agent
Giardia lamblia (G. intestinalis, G. duodenalis), a flagellate protozoan1

Common clinical features
Varies from asymptomatic (approximately 25% of acute infections) to severe diarrhoea with malaise, flatulence, foul smelling greasy stools, abdominal cramps, bloating, nausea and anorexia2.


  • Giardia lamblia is the most frequently isolated intestinal protozoa in the world. It occurs in the aquatic environment throughout the world and is resistant to disinfectants used in drinking water treatment.
  • Prevalence is higher in areas of poor sanitation particularly in developing countries.
  • There were 3,169 laboratory confirmed cases of Giardia in England and Wales in 2004.
  • In the UK children < 5 years and adults aged 25-39 are most commonly affected. Groups with high rates of infection also include residents of institutions, travellers, gay men and the immunocompromised2.
  • Giardia is a common cause of traveller's diarrhoea.

Humans, possibly beaver and other wild and domestic animals1.

Mode of transmission
Person to person via the faecal oral route.

Ingestion of cysts in faecally contaminated drinking and recreational water.

Incubation period
Commonly 3-25 days or longer, median 7-10 days.

Period of Communicability
During period of infection.

Laboratory Diagnosis
Diagnosis is by identification of cysts or trophozoites in faeces. Repeated samplings may be required.

Commonly used antibiotics include metronidazole and tinidazole. 

Prevention and control

  • There is no vaccine or chemoprophylaxis for Giardia.
  • Follow correct food hygiene practices for food preparation and cooking in domestic and commercial kitchens.
  • Treatment of water supplies.
  • Advice to travellers abroad on safe food and water.
  • Hand washing.


  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006