Giardiasis is an intestinal infection caused by Giardia lamblia — the most common protozoan cause of diarrhoeal disease globally. Infection occurs by ingesting Giardia cysts in contaminated water or food, or through person-to-person fecal-oral contact. Giardia attaches to the small intestinal wall, causing malabsorption of fats and other nutrients. The result: prolonged diarrhoea with characteristic greasy, malodorous stools; bloating; flatulence; and weight loss — without blood, which distinguishes giardiasis from invasive bacterial or amoebic infection.

What is "beaver fever"?

Beaver fever is the colloquial name for waterborne giardiasis — so named because beavers and other wild animals (muskrats, deer, domestic animals) contaminate streams and lakes with Giardia cysts. Even clear, apparently pristine mountain streams can be heavily contaminated with Giardia. Hikers, campers and wilderness travelers should never drink untreated surface water — use filtration (0.2-1 micron filter effective), boiling (1 minute at altitude), or chemical treatment (iodine or chlorine dioxide — chlorine alone is less reliable).

How does Giardia cause symptoms?

Giardia trophozoites attach to the brush border of small intestinal enterocytes via a sucking disc — physically disrupting the tight junctions between cells and directly damaging brush border enzymes (disaccharidases including lactase). This causes malabsorption of fats, carbohydrates and proteins. The malabsorbed fat and carbohydrate reaching the large intestine are fermented by colonic bacteria — causing the bloating and flatulence characteristic of giardiasis. Villi are structurally relatively preserved (unlike coeliac disease) but function is impaired.

Who is most susceptible?

Children: highest prevalence globally; particularly common in childcare settings (person-to-person fecal-oral spread). Travellers: travellers' diarrhoea from contaminated food/water in endemic settings. Wilderness recreationists: waterborne exposure. Immunocompromised patients: especially those with humoral immune deficiencies (IgA deficiency, CVID) — Giardia is poorly controlled without IgA-mediated mucosal immunity; these patients develop chronic giardiasis.

How is giardiasis treated?

First-line: metronidazole 250mg three times daily × 5-7 days (or tinidazole 2g single dose — equally effective, more convenient). Alternatives: nitazoxanide (preferred in children and immunocompromised); albendazole (less evidence). Treatment of sexual partner(s) in MSM-associated giardiasis prevents reinfection. Re-test 2-4 weeks after treatment if symptoms persist — relapse can occur from persistent cysts or reinfection. Note: metronidazole-resistant Giardia is increasingly reported — alternative agents or combination therapy may be needed.

How does GMJ News cover giardiasis?

GMJ News covers WHO giardiasis burden data, beaver fever wilderness risk, steatorrhoea clinical recognition, metronidazole and tinidazole treatment, Giardia antigen testing, water treatment, and post-infectious IBS. Giardiasis is common in Georgia — particularly in rural areas and among hikers in the Greater and Lesser Caucasus mountains — relevant to PHIG's NTD and food/water safety programme.

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Giardiasis

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

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Giardiasis — caused by the flagellate protozoan Giardia lamblia (also called G. intestinalis or G. duodenalis) — is the most common protozoan cause of diarrhoeal disease globally, causing approximately 300 million symptomatic infections per year through contaminated water and food in both LMICs and, via recreational water exposure (the classic “beaver fever”), in HICs (WHO). Giardia attaches to the small intestinal wall and causes a characteristic syndrome of malodorous greasy floating stools (steatorrhoea), bloating, flatulence and abdominal cramps without blood — a clinically recognisable pattern. In children, chronic giardiasis causes malabsorption, nutritional deficiency and growth faltering. Metronidazole remains the first-line treatment.

Key messages

Most common protozoan diarrheal globally — 300 million+

Giardiasis is the most common protozoan intestinal infection globally, causing approximately 300 million symptomatic infections per year — transmitted through contaminated water, food and person-to-person contact in both LMICs and HICs (WHO).

Greasy floating stools — the clinical clue

Giardia causes a characteristic malabsorptive diarrhoea: malodorous, greasy, floating, pale stools (steatorrhoea from fat malabsorption); bloating; flatulence; abdominal cramps; without blood or mucus. This fat-malabsorptive pattern reflects Giardia's mechanism of action (disrupting brush border enzyme function and coating the absorptive surface).

No blood — distinguishes from shigella/amoebiasis

A critical clinical distinction: Giardia diarrhoea NEVER contains blood. Blood in stool with fever and cramps indicates bacterial dysentery (Shigella, Campylobacter) or amoebic colitis — not Giardia.

Children — malnutrition and growth faltering

In LMICs, chronic Giardia infection in children causes malabsorption, failure to thrive, stunted growth and nutritional deficiencies — compounding the already high burden of childhood undernutrition in endemic areas.

Beaver fever — wilderness water exposure

G. lamblia is a notorious risk in wilderness water — even apparently clear mountain streams or rivers can be contaminated by wild animal (beaver, muskrat, deer) faeces. Hikers and campers should always filter or purify backcountry water.

Metronidazole first-line

Metronidazole (250mg three times daily × 5-7 days) is the first-line treatment. Tinidazole (single dose 2g) is more convenient and equally effective. Nitazoxanide is preferred in children and HIV patients.

Key statistics

~300M

symptomatic giardiasis cases/year globally

WHO

most common protozoan cause of diarrheal disease worldwide

WHO

WHO NTD

Giardia listed as WHO Neglected Tropical Disease since 2004

WHO

blood in stool — Giardia never causes dysentery

WHO/Clinical

15%

estimated prevalence in LMICs

WHO

3-5%

prevalence in HICs

WHO

Giardiasis transmission routes — relative importance (% of cases)

Source: WHO. Contaminated water dominates globally; person-to-person important in childcare settings.

Glossary of key terms

Giardia lamblia
WHOA flagellate protozoan — tear-drop shaped trophozoites with two nuclei (giving the "owl face" appearance) that attach to the small intestinal epithelium via a sucking disc. Cysts are the infectious form — resistant to chlorination, UV (high doses needed) and most disinfectants.

Steatorrhoea
WHO/ClinicalFatty stools — pale, bulky, greasy, floating, with a particularly offensive odour. Caused by fat malabsorption from Giardia disrupting brush border enzymes (lactase, alkaline phosphatase) and coating the absorptive surface of the small intestinal villi. Characteristic of giardiasis; also seen in coeliac disease, chronic pancreatitis.

Post-infectious IBS
WHO/ResearchApproximately 10-15% of people who recover from Giardia infection develop post-infectious irritable bowel syndrome (PI-IBS) — ongoing GI symptoms (bloating, altered bowel habit, abdominal discomfort) lasting months to years after successful parasite eradication.

Giardia cyst resistance
WHO/Water treatmentGiardia cysts are highly resistant to standard water chlorination — making waterborne Giardia outbreaks possible even in chlorinated municipal water systems (if filtration fails). Effective water treatment requires filtration (removes cysts) or UV irradiation at sufficient dose. Bottled water and boiling also eliminate cysts.

Stool antigen test
WHO/DiagnosisThe recommended first-line diagnostic test — immunochromatographic or ELISA assay detecting Giardia-specific antigen in stool. Sensitivity approximately 85-98%; specificity >99%. More sensitive than microscopy (which requires three separate stool samples examined by experienced microscopist). Also available for simultaneous Cryptosporidium and Giardia detection.

Tinidazole (single-dose)
WHO EMLA nitroimidazole antiparasitic — a single 2g oral dose for giardiasis, achieving approximately 90% cure rates. More convenient than metronidazole (multi-day course). Both are on the WHO Essential Medicines List.

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