Giardia is a microscopic parasite that causes an illness called giardiasis. Giardia is one of the main causes of diarrhea in the United States. Infection occurs when the parasites are ingested in contaminated water or food or via person-to-person contact.
In addition to diarrhea, symptoms of giardiasis include nausea, vomiting, cramps, abdominal distension and copious amounts of intestinal gas. Loss of appetite and low-grade fever are other possible symptoms. People who develop this condition often get better within a few weeks without treatment, but for those with severe or persistent symptoms, antibiotics are prescribed. Those treated with medication normally recover within a week.