Giradiasis is an illness caused by a parasite called Giardia intestinalis . It lives in soil, food and water. It may also be on surfaces that have been contaminated with waste. You can become infected if you swallow the parasite. Diarrhea is the main symptom of giardia infection. Others include Passing gas Greasy stools Stomach cramps Upset stomach or nausea These symptoms may lead to weight loss and loss of body fluids. Some people have no symptoms at all. Symptoms of infection often last two to six weeks. Doctors use several drugs to treat it. The best way to prevent giardia infection is to practice good hygiene, including frequent hand washing. You should not drink water that may be contaminated. You should also peel or wash fresh fruit and vegetables before eating.