Illness & Symptoms

Giardiasis is the most frequently diagnosed intestinal parasitic disease in the United States and among travelers with chronic diarrhea 1. Signs and symptoms may vary and can last for 1 to 2 weeks or longer 2,5. In some cases, people infected with Giardia have no symptoms 2-4.

Acute symptoms include 2,4,6:

  • Diarrhea
  • Gas
  • Greasy stools that tend to float
  • Stomach or abdominal cramps
  • Upset stomach or nausea/vomiting
  • Dehydration (loss of fluids)

Other, less common symptoms include itchy skin, hives, and swelling of the eye and joints 2,7,8. Sometimes, the symptoms of giardiasis might seem to resolve, only to come back again after several days or weeks. Giardiasis can cause weight loss and failure to absorb fat, lactose, vitamin A and vitamin B12 2,4,9-12.

In children, severe giardiasis might delay physical and mental growth, slow development, and cause malnutrition 2,11,13-17.

Giardia trophozoites under a microscope.

Giardia trophozoites stained with trichrome. Credit: Waterborne Disease Prevention Branch, CDC

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  11. Farthing MJ. Giardia comes of age: progress in epidemiology, immunology and chemotherapy. Cdc-pdf[PDF – 4 pages]External J Antimicrob Chemother. 1992;30(5):563-6.
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  13. Sullivan PB, Marsh MN, Phillips MB, Dewit O, Neale G, Cevallos AM, Yamson P, Farthing MJ. Prevalence and treatment of giardiasis in chronic diarrhoea and malnutrition. Cdc-pdf[PDF – 3 pages]External Arch Dis Child. 1991;66(3):304-6.
  14. Farthing MJ, Mata L, Urrutia JJ, Kronmal RA. Natural history of Giardia infection of infants and children in rural Guatemala and its impact on physical growth.External Am J Clin Nutr. 1986;43(3):395-405.
  15. Berkman DS, Lescano AG, Gilman RH, Lopez SL, Black MM. Effects of stunting, diarrhoeal disease, and parasitic infection during infancy on cognition in late childhood: a follow-up study.External Lancet. 2002;359(9306):564-71.
  16. Newman RD, Moore SR, Lima AA, Nataro JP, Guerrant RL, Sears CL. A longitudinal study of Giardia lamblia infection in north-east Brazilian children.External Trop Med Int Health. 2001;6(8):624-34.
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