Giardiasis is a parasitic disease of the upper small intestine caused by the non-invasive protozoan Giardia duodenalis (synonyms G. lamblia and G. intestinalis) [1][3][2]. The parasite has a two-stage life cycle comprising an infectious cyst form and a trophozoite form that colonizes the small intestine, with cysts excreted in feces serving as the transmissible stage [2].
Disease overview
Parasitic Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026
Giardiasis is a parasitic diarrheal illness caused by Giardia duodenalis (also known as G. lamblia or G. intestinalis) and represents a leading cause of waterborne and foodborne diarrhea, daycare-associated outbreaks, and traveler's diarrhea worldwide [1][2]. The infection is especially common in children and travelers, with an estimated 280 million people affected annually, and asymptomatic infections are equally common [3][2]. Clinical presentation ranges from asymptomatic carriage to acute or chronic diarrhea with malabsorption, and treatment-refractory disease is increasingly reported, making giardiasis a persistent global public-health concern [1][4][3].
Read the full clinical and epidemiological profile 6
Clinical manifestations range from asymptomatic infection to severe diarrhea; approximately 50–75% of infected children are asymptomatic, while symptomatic cases may present with acute or chronic diarrhea, including steatorrhea characterized by greasy, foul-smelling, floating stools [1][2]. Accompanying features include abdominal pain, weight loss, bloating, weakness from dehydration and malabsorption, and less commonly skin rash, hives, and joint swelling [2]. Symptoms typically develop 1–3 weeks after exposure and, without treatment, may last two to six weeks or longer, with some infections progressing to chronic disease or post-infectious sequelae such as irritable bowel syndrome and food allergies [3][2].
Giardiasis is a globally distributed cause of diarrhea and intestinal enteropathy [4]. The disease is a recognized cause of waterborne and foodborne diarrhea, daycare-center outbreaks, and traveler's diarrhea [1]. Treatment-refractory giardiasis appears to be increasing, with reports that 5-nitroimidazole-refractory infection may occur in up to 50% of cases in some clinical series, underscoring the evolving therapeutic challenge [4].
Transmission occurs via the fecal-oral route when Giardia cysts excreted in feces contaminate food, drinking water, or recreational water that is subsequently ingested [1][2]. Person-to-person spread is well documented, and zoonotic transmission can also occur, particularly through contact with infected pets [1][2]. Cysts are environmentally resilient and may remain viable in cold water for nearly three months, and ingestion of only a small number of cysts is sufficient to establish infection in a new host [2].
Prevention centers on interrupting the fecal-oral route through proper personal hygiene, safe handling and thorough cooking of food, and adequate sanitation or treatment of drinking and recreational water [1][2]. In high-risk settings such as daycare centers and during travel to endemic regions, attention to hand hygiene, avoidance of untreated water, and care with food preparation are particularly important to reduce transmission [1][2].
- 1 Leung AKC et al. Giardiasis: An Overview. Recent Pat Inflamm Allergy Drug Discov. 2019. PMID: 31210116. doi: 10.2174/1872213X13666190618124901. PubMed: https://pubmed.ncbi.nlm.nih.gov/31210116/
- 2 Wikipedia contributors. Giardiasis - Wikipedia [Internet]. Wikipedia. cited 2 Sept 2026. Available from: https://en.wikipedia.org/wiki/Giardiasis
- 3 Einarsson E et al. An up-date on Giardia and giardiasis. Curr Opin Microbiol. 2016 Dec. PMID: 27501461. doi: 10.1016/j.mib.2016.07.019. PubMed: https://pubmed.ncbi.nlm.nih.gov/27501461/
- 4 Mørch K et al. Giardiasis treatment: an update with a focus on refractory disease. Curr Opin Infect Dis. 2020 Oct. PMID: 32773501. doi: 10.1097/QCO.0000000000000668. PubMed: https://pubmed.ncbi.nlm.nih.gov/32773501/
- 5 McFarland LV et al. Systematic review and meta-analysis of Saccharomyces boulardii in adult patients. World J Gastroenterol. 2010 May 14. PMID: 20458757. doi: 10.3748/wjg.v16.i18.2202. PubMed: https://pubmed.ncbi.nlm.nih.gov/20458757/
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Recent related research
A Mathematical Model for the Transmission of Giardiasis Incorporating Resistance Strain and Second Line of Treatment
International Journal of Development Mathematics (IJDM)
Nitroimidazole - albendazole combination therapy, quinacrine use, and risk factors in nitroimidazole-refractory giardiasis: a prospective multicentre observational study
BMC Infectious Diseases
Epidemiology and management of nitroimidazole-refractory giardiasis
Journal of Travel Medicine
Intestinal protozoan infections among children 0-168 months with diarrhea in Mozambique: June 2014 - January 2018
PLOS Neglected Tropical Diseases
Risk factors for sporadic Giardia infection in the USA: a case-control study in Colorado and Minnesota
Epidemiology and Infection
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