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Causes
By Mayo Clinic staff
Giardia takes two forms
Giardia is caused by the parasite Giardia intestinalis (also called Giardia lamblia). The giardia parasite has two forms:
- Active. The active form of giardia lives in the intestines of an infected animal or human.
- Inactive cyst. An inactive cyst form can survive for months in the environment.
When you ingest the inactive cysts, their hard shells break down in your stomach, releasing the parasites. The parasites then attach to the wall of your small intestine, eventually reproducing by the millions and damaging the intestinal wall. This interferes with your ability to absorb food, leading to diarrhea and weight loss.
In time, the parasites detach from the small intestine, transform back into cysts and are shed in your feces. They can survive in soil or water for long periods until they're ingested by another host.
How you can get giardia infection
You're likely to pick up the parasites in one of three ways:
- In water. This is the main source of giardia infection. The parasites are found in lakes, ponds, rivers and streams worldwide, as well as in municipal water supplies, wells, cisterns, swimming pools, water parks and spas. Giardia parasites have even turned up in touch tanks in aquariums and museums. Ground and surface water can become contaminated from agricultural runoff and wastewater discharge. Because giardiasis affects beavers, muskrats, small rodents and a variety of birds, reptiles and fish, water can also become contaminated from animal feces. Children in diapers and people with diarrhea may accidentally contaminate pools and spas. You can become infected if you drink from streams or lakes that contain the parasites, drink contaminated tap water at home or abroad, or accidentally swallow water from a tainted pool or spa.
- In food. Giardia parasites can be transmitted through food — either because food handlers with giardiasis don't wash their hands or because raw produce is irrigated or washed with contaminated water. Because cooking food kills giardia, food is a less common source of infection than water is, especially in industrialized countries. However, outbreaks can occur through ice and infected food service workers.
- By direct contact. You can get giardiasis if your hands become contaminated with fecal matter — parents changing a child's diapers are especially at risk. So are child care workers and children in child care centers. The giardia parasite can also spread through anal sex.
