Giardiasis

Key facts

• Giardiasis is an intestinal infection caused by Giardia lamblia, a microscopic parasite spread through contaminated water and food.
• It causes persistent, greasy diarrhoea, bloating, cramps and excess wind that can drag on for weeks; some people carry the parasite with no noticeable symptoms.
• First-line treatment is an antiparasitic: tinidazole, often a single dose, or ornidazole over a short course; albendazole is a broader alternative.
• See a doctor if symptoms don't improve after treatment, or if you notice blood in the stool or a high fever.

What giardiasis is

Giardiasis is one of the most common gut parasite infections worldwide. It is caused by Giardia lamblia, a microscopic organism that gets into the body through water or food contaminated with infected faeces, including from unwashed hands or poorly treated water supplies.

Symptoms and what sets it apart

The infection typically causes persistent, greasy diarrhoea that floats, along with bloating, stomach cramps, nausea and excessive wind. Fatigue is common. Unlike bacterial food poisoning, giardiasis tends to drag on for weeks rather than days, and some people carry the parasite without noticeable symptoms.

How giardiasis is treated

Giardiasis responds well to antiparasitic medicines. The most commonly used agents are tinidazole, which is often given as a single dose, and ornidazole, taken over a short course. Albendazole is a broader antiparasitic that is sometimes used where tinidazole-class medicines aren't available. Staying well hydrated throughout treatment helps the gut recover, especially if diarrhoea has been prolonged.

When to see a doctor

Symptoms that don't improve after a full treatment course, or that include blood in the stool or a high fever, warrant prompt medical review.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.