DurgicalDurgical
EN
Open the app

Conditions · Infectious and tropical diseases

Giardiasis !

Giardiasis is a gut infection by the parasite Giardia, spread by contaminated water, that causes greasy diarrhoea, bloating and weight loss.

Updated 2026-11-01

Structures involved

Tap one to see what it is and open it in 3D.

Microorganisms that cause it

Why it happens

What it is

An infection of the small intestine by the flagellated protozoan Giardia duodenalis (also called G. lamblia or G. intestinalis), causing acute or chronic non-bloody diarrhoea and malabsorption; many infections are asymptomatic.

Who gets it

One of the most common intestinal parasites in the world and in Latin America. In Colombia it is frequent in children, especially in rural areas and day-care settings without safe water; it also causes outbreaks from contaminated water supplies and illness in travellers and hikers.

Causes

  • Giardia duodenalis cysts, which are resistant to chlorine and survive in cold water
  • Faecal-oral spread through water, food, hands or surfaces; a few cysts are enough to infect
  • Zoonotic transmission from some animals is possible

Risk factors

  • Drinking untreated water (wells, streams, poorly treated supplies)
  • Young children, day-care centres and their caregivers
  • Poor sanitation and crowding
  • Travel and outdoor activities with untreated water
  • Humoral immunodeficiency (common variable immunodeficiency, X-linked agammaglobulinaemia) and IgA deficiency
  • Oral-anal sexual contact

Pathophysiology

Swallowed cysts release trophozoites in the duodenum, which attach to the epithelium with a ventral sucking disc but do not invade. They shorten the microvilli, reduce brush-border enzymes such as lactase and increase epithelial permeability, causing malabsorption of fat and sugars. Trophozoites encyst further down the bowel and cysts are passed in the stool.

Classification

  • Asymptomatic infection (carriage)
  • Acute giardiasis
  • Chronic giardiasis with malabsorption and weight loss

Symptoms and signs

  • Watery, then greasy, foul-smelling, floating stools without blood
  • Bloating, flatulence, abdominal cramps and sulphur-smelling belching
  • Nausea and loss of appetite
  • Fatigue and weight loss in chronic cases
  • Poor growth in children with long-standing infection

Diagnosis

Clinical
Suspected with prolonged non-bloody diarrhoea, bloating and malabsorption after exposure to untreated water, day care or travel. Treatment may start on history when testing is limited.
Tests
Stool antigen tests (immunoassay or immunofluorescence) or molecular panels are more sensitive than microscopy; microscopy for cysts or trophozoites needs several samples because shedding is intermittent. Small-bowel biopsy or duodenal aspirate is rarely needed.
Imaging
Not needed for diagnosis.

Differential diagnosis

  • Viral gastroenteritis
  • Cryptosporidiosis and other intestinal protozoa
  • Coeliac disease
  • Lactose intolerance
  • Irritable bowel syndrome
  • Small intestinal bacterial overgrowth

Goal of treatment

Eradicate the parasite in symptomatic people, correct dehydration and nutrition, and prevent spread to household and day-care contacts.

Treatment

Acute
Rehydration when needed, especially in infants and pregnant women.
Medical
Antiparasitic drugs: nitroimidazoles (tinidazole, metronidazole) or nitazoxanide; options in pregnancy are chosen carefully. Combination therapy is used for refractory cases.
Follow-up
Retest stool when symptoms persist, check for reinfection or incomplete treatment, and evaluate for immunodeficiency in recurrent cases; temporary lactose intolerance may last weeks after cure.
Lifestyle
Handwashing, safe or boiled water, and keeping ill children out of day care and swimming pools until diarrhoea resolves.

Complications

  • Dehydration
  • Malabsorption of fat, fat-soluble vitamins and vitamin B12
  • Acquired lactose intolerance after the infection
  • Growth faltering and malnutrition in children
  • Post-infectious irritable bowel syndrome and chronic fatigue

Prognosis

Usually cured with treatment; some infections resolve on their own. Reinfection is common in endemic areas, and symptoms such as lactose intolerance may persist for weeks.

Prevention

  • Safe, filtered or boiled drinking water (chlorine alone does not reliably kill cysts)
  • Handwashing, especially after nappy changes and before eating
  • Washing raw produce
  • Excluding children with diarrhoea from day care and pools

Test yourself

Think of the answer, then tap the question to see it.

Where does Giardia live and does it invade the mucosa?

In the duodenum and jejunum, attached by a ventral sucking disc; it does not invade, so stools are not bloody.

What type of stool is classic for giardiasis?

Greasy, foul-smelling, floating stools (steatorrhoea) with bloating and flatulence.

Which immune deficiency predisposes to chronic giardiasis?

Humoral deficiencies such as IgA deficiency, common variable immunodeficiency and X-linked agammaglobulinaemia.

Which drug classes treat giardiasis?

Nitroimidazoles (tinidazole, metronidazole) or nitazoxanide.

Add to my cards (4)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Giardia infection: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024); Patient Care for Giardia Infection | Giardia | CDC (Centers for Disease Control and Prevention, 2024).

← All conditions

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.

Duodenum highlighted on the Durgical 3D model