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  • Writer's pictureFibonacciMD


AKA Beaver Fever



By Cheng-Hung Tai, M.D. and

Giardiasis is a disease caused by the

parasite Giardia (Giardia duodenalis, lamblia, and intestinalis). Common symptoms include greasy loose stools or diarrhea, abdominal cramping,

weight loss, nausea/vomiting, and fever.

Symptoms typically start 1 to 3 weeks after infection and may last up to 2 to 6 weeks in immune-competent patients. It is caused by the spread of Giardia cysts found within contaminated food or water, where the host (humans) would ingest. It is the most common human parasitic disease worldwide, and most commonly seen in the developing world, with prevalence reported as high as 40%.

It is important to note that there are two morphologic forms of Giardia: cysts and trophozoites. The cysts are the infectious form, whereas the trophozoites are the active, flagellated parasitic form that attaches to small bowel mucosal surfaces. This attachment ultimately causes malabsorption by breaking down digestive enzymes at the brush border of the small intestine.

Diagnostic Evaluation

Diagnosis for giardiasis includes a detailed history and physical. For example, a recent traveler to a resource-poor country, given a history of consuming poorly-prepared foods, would place the individual at a higher risk for Giardiasis. Common lab tests include: microscopy stool studies for ova and parasites (demonstration of microscopic cysts or trophozoites in stool samples) and stool antigen/nucleic acid detection assays including immunoassay antigen detection (ELISA) and PCR-based molecular methods. The stool assays are the most sensitive tests. Nucleic acid amplication assays for Giardia are often utilized for rapid panel detection on stool samples.

Giardia trophozoite
Giardia trophozoite


  • Maintain proper hand hygiene

  • Avoid drinking untreated water from rivers or lakes

  • Boil untreated water for at least 1 minute or filter water

  • “Cook it, boil it, peel it, or forget it” (with respect to food, fruits and vegetables and water)

Treatment Options

The treatment for giardiasis involves symptom management with supportive care and antimicrobial therapy. Oral rehydration is imperative, as patients that are symptomatic may have significant volume loss due to diarrhea. Hand hygiene is important to prevent the spread of infection as well. Those that are asymptomatic (incidental finding of giardiasis) without high risk of transmission (e.g. food-handlers), not initiating antimicrobial treatment could be considered. Although they would continue to shed cysts until resolution (self-limiting disease). Most patients treated with antimicrobial therapy will experience symptom resolution within 5-7 days. The preferred agents include nitazoxanide, tinidazole, and metronidazole (e.g. Flagyl 3 times a day for 5-10 days). Other agents with efficacy include albendazole, mebendazole, and paromomycin. In patients with recurrent symptoms despite treatment, it is important to

consider treatment failure (due to drug resistance), immunosuppression, or possibly treatment non-adherence. Repeat stool testing should be considered, and if immunodeficiencies are suspected, appropriate studies should be sent (IgA deficiency, HIV, etc.).


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Sources and further reading:

Schlagenhauf P, Weld L, Goorhuis A, et al. Travel-associated infection presenting in Europe (2008-12): an analysis of EuroTravNet longitudinal, surveillance data, and evaluation of the effect of the pre-travel consultation. Lancet Infect Dis. 2015;15(1):55-64.

Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. Clin Infect Dis. 2017;65(12):e45-e80.

Ross AG, Olds GR, Cripps AW, Farrar JJ, Mcmanus DP. Enteropathogens and chronic illness in returning travelers. N Engl J Med. 2013;368(19):1817-25.

Desai, A. Giardiasis. JAMA. 2021;325(13):1356. doi:10.1001/jama.2020.10289

Hooshyar H, Rostamkhani P, Arbabi M, Delavari M. Giardia lamblia infection: review of current diagnostic strategies. Gastroenterol Hepatol Bed Bench. 2019; 12(1): 3–12. PMCID: PMC6441489

PMID: 30949313


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