> Table of Contents > Giardiasis
Iryna Matkovska, DO
Deborah Pierce, DO
Merle A. Carter, MD, FACEP
image BASICS
  • Intestinal infection caused by the protozoan parasite Giardia lamblia:
    • G. lamblia is also called Giardia duodenalis and Giardia intestinalis.
  • Infection results from ingestion of cysts, which transform into trophozoites:
    • Trophozoites colonize the small intestine and cause symptoms.
    • Cycle is continued when the trophozoites encyst in the small intestine and are subsequently transmitted through water, food, or hands contaminated by feces of infected person.
  • Most infections result from fecal-oral transmission or ingestion of contaminated water (e.g., swimming).
  • Less commonly, giardiasis is the result of contaminated food.
  • Predominant age:
    • All ages but most common in early childhood ages 1 to 9 years and adults 35 to 44 years
  • Predominant gender:
    • Male > female (slightly)
  • Minimal seasonal variability; slight increase in summer
Pediatric Considerations
Most common in early childhood
  • 5% of patients with stools submitted for ova and parasite exams
  • > 19,000 cases/year in reportable U.S. states:
    • Giardia is not reportable in Indiana, Kentucky, Mississippi, North Carolina, and Texas.
Giardia trophozoites colonize the surface of the proximal small intestine: The mechanism of diarrhea is unknown.
No known genetic risk factors
  • Daycare centers
  • Anal intercourse
  • Wilderness camping
  • Travel to developing countries
  • Children adopted from developing countries
  • Public swimming pools
  • Pets with Gardia infection/diarrhea
  • Hand hygiene
  • Water purification when camping and when traveling to developing countries
  • Properly cook all foods.
Hypogammaglobulinemia and possibly IgA deficiency: diarrhea more severe and prolonged in these patients
  • Typically normal vital signs
  • Nonspecific; abdominal exam; may have bloating tenderness or increased bowel sounds
  • Cryptosporidiosis, isosporiasis, cyclosporiasis
  • Other causes of malabsorption include celiac sprue, tropical sprue, bacterial overgrowth syndromes, and Crohn ileitis.
  • Irritable bowel (diarrhea without weight loss)
Initial Tests (lab, imaging)
  • Stool for ova and parasites:
    • Repeat 3 times on separate days
    • Cysts in fixed or fresh stools, and occasionally, trophozoites are found in fresh diarrheal stools.
  • Limitations: experienced operator, intermittent shedding of ova may not be present in stool sample, labor intensive
    • ELISA: sensitivity and specificity of 100% and 91.5% respectively (compared to 50-70% sensitivity using microscopy) (1)[B].
  • Polymerase chain reaction (PCR) techniques are more sensitive than microscopy but have not been widely adopted due to high cost.
  • Rapid detection tests have been studied showing high detection rates not widely available (2)[B].
Follow-Up Tests & Special Considerations
String test (Entero-test):
  • A gelatin capsule on a string is swallowed and left in the duodenum for several hours or overnight. The string is removed and visualized microscopically.
Diagnostic Procedures/Other
Esophagogastroduodenoscopy (EGD) with biopsy and sample of small intestinal fluid
Test Interpretation
Intestinal biopsy shows flattened, mild lymphocytic infiltration and trophozoites on the surface.
Outpatient for mild cases; inpatient if symptoms are severe enough to cause dehydration warranting parenteral fluid replacement
  • Medical therapy for all infected individuals
  • Fluid replacement if dehydrated
First Line
  • Metronidazole (Flagyl): 250 mg PO TID for 5 to 7 days (2)[B]
  • Tinidazole: 2 g PO single dose (50 mg/kg up to 2 g for children)
  • Albendazole: 400 mg/day PO for 5 days:
    • Albendazole has comparable effectiveness to metronidazole with fewer side effects and lower cost.
  • Precautions:
    • Theoretical risk of carcinogenesis with metronidazole
  • Significant possible interactions: occasional disulfiram reaction with metronidazole or tinidazole
Pregnancy Considerations
Medications to treat giardiasis are relatively contraindicated during pregnancy; consider appropriate consultation with infectious disease or maternal-fetal medicine specialist.
Pediatric Considerations
In one study, administration of vitamin A reduced prevalence of G. lamblia (3)[A].

Second Line
  • Furazolidone: 8 mg/kg/day TID for 10 days (slightly less effective but commonly used in pediatrics because it is well tolerated); not available in United States
  • Paromomycin (Humatin): a nonabsorbable aminoglycoside that is probably less effective but commonly recommended in pregnancy because of lower risk of teratogenicity
  • Quinacrine: 100 mg TID for 5 to 7 days; withdrawn from the U.S. market
  • Nitazoxanide suspension was approved by the FDA in 2003 for treatment of giardiasis in children 1 to 11 years. Children aged 1 to 4 years receive 100 mg BID and age 5 to 11 years receive 200 mg BID for 3 days.
  • Two other nitroimidazole antibiotics, ornidazole and secnidazole, are effective against Giardia but are not available in the United States.
  • There have been anecdotal reports of herbal products containing Mentha crispa being effective in the treatment of Giardia. When studied, it was much less effective than secnidazole (a metronidazole analog).
  • A recent study showed tetrahydrolipstatin (Orlistat) had activity against Giardia (may be a potential treatment option in the future for patients who are resistant to metronidazole) (4)[C].
  • In mouse studies, auranofin, miltefosine, disulfiram, and omeprazole have all shown effective activity against G. lamblia. Research is still needed in humans (5,6,7,8)[C].
Patient Monitoring
Symptoms, weight, stool exams if patients fail to improve
Low lactose, low fat, monitor for dehydration
  • Hand washing may be more important than water purification to prevent transmission in outdoor enthusiasts.
  • Lactose intolerance may follow Giardia infection and cause of persistent diarrhea posttreatment. Consider low-lactose diet.
  • CDC Facts about Giardia and Swimming Pools: http://www.cdc.gov/healthywater/pdf/swimming/resources/giardia-factsheet.pdf
    • Don't swim if you have diarrhea.
    • Wash hands with soap after changing diapers before returning to the pool.
    • Do not ingest pool, lake, or river water.
    • Use chlorine to kill Gardia in water used for recreational activities.
  • Untreated giardiasis lasts for weeks.
  • Most (90%) patients respond to treatment within a few days:
    • Most nonresponders or relapses respond to a second course with the same or a different agent.
1. Jahan N, Khatoon R, Ahmad S. A comparison of microscopy and enzyme linked immunosorbent assay for diagnosis of Giardia lamblia in human faecal specimens. J Clin Diagn Res. 2014;8(11): DC04-DC06.
2. Van den Bossche D, Cnops L, Verschueren J, et al. Comparison of four rapid diagnostic tests, ELISA, microscopy and PCR for the detection of Giardia lamblia, Cryptosporidium spp. and Entamoeba histolytica in feces. J Microbiol Methods. 2015; 110:78-84.
3. Lima AA, Soares AM, Lima NL, et al. Effects of vitamin A supplementation on intestinal barrier function, growth, total parasitic, and specific Giardia spp infections in Brazilian children: a prospective randomized, double-blind, placebo-controlled trial. J Pediatr Gastroenterol Nutr. 2010;50(3):309-315.
4. Hahn J, Seeber F, Kolodziej H, et al. High sensitivity of Giardia duodenalis to tetrahydolipstatin (orlistat) in vitro. PLoS One. 2013;8(8):e71597.
5. Tejman-Yarden N, Miyamoto Y, Leitsch D, et al. A reprofiled drug, auranofin, is effective against metronidazole-resistant Giardia lamblia. Antimicrob Agents Chemother. 2013;57(5):2029-2035.
6. Eissa MM, Amer EI. Giardia lamblia: a new target for miltefosine. Int J Parasitol. 2012;42(5):443-452.
7. Galkin A, Kulakova L, Lim K, et al. Structural basis for inactivation of Giardia lamblia carbamate kinase by disulfiram. J Biol Chem. 2014;289(15): 10502-10509.
8. Reyes-Vivas H, de la Mora-de la Mora I, Castillo-Villanueva A, et al. Giardial triosephosphate isomerase as possible target of the cytotoxic effect of omeprazole in Giardia lamblia. Antimicrob Agents Chemother. 2014;58(12):7072-7082.
Additional Reading
  • Almirall P, Escobedo AA, Ayala I, et al. Mebendazole compared with secnidazole in the treatment of adult giardiasis: a randomised, no-inferiority, open clinical trial. J Parasitol Res. 2011;2011:636857.
  • Cañete R, Rodríguez P, Mesa L, et al. Albendazole versus metronidazole in the treatment of adult giardiasis: a randomized, double-blind, clinical trial. Curr Med Res Opin. 2012;28(1):149-154.
  • Lal A, Hales S, French N, et al. Seasonality in human zoonotic enteric diseases: a systematic review. PLoS One. 2012;7(4):e31883.
  • Solaymani-Mohammadi S, Genkinger JM, Loffredo CA, et al. A meta-analysis of the effectiveness of albendazole compared with metronidazole as treatments for infections with Giardia duodenalis. PLoS Negl Trop Dis. 2010;4(5):e682.
  • Teles NS, Fechine FV, Viana FA, et al. Evaluation of the therapeutic efficacy of Mentha crispa in the treatment of giardiasis. Contemp Clin Trials. 2011; 32(6):809-813.
  • Yoder JS, Harral C, Beach MJ. Giardiasis surveillance— United States, 2006-2008. MMWR Surveill Summ. 2010;59(6):15-25.
See Also
Algorithm: Diarrhea, Chronic
A07.1 Giardiasis [lambliasis]
Clinical Pearls
  • Daycare facilities and public swimming pools are common sources of Giardia (don't assume camping or travel is required).
  • Metronidazole has high cure rates (but is often poorly tolerated).
  • Most treatment failures respond to a second course of antibiotics (with same or other drugs).
  • A single FA or ELISA is as sensitive as three stool samples for ova and parasites for detecting Giardia.