giardiasis

giardiasis A contagious form of diarrhea caused by the parasite Giardia lamblia. Transmission is most common by direct contact with infected feces or by eating food or drinking water contaminated by feces. Giardia is one of the most common intestinal parasites in the world, and the disease is most prevalent in developing countries. Giardia is also a major cause of waterborne outbreaks of diarrhea in the US. It particularly affects diapered children and toddlers being toilet-trained. Symptoms include a sudden explosive, watery, foul-smelling diarrhea; excessive gas; abdominal pain; bloating; nausea; tiredness; and loss of appetite. Fever is unusual. If not treated, giardiasis can last for months or even years. The diagnosis is made by microscopic identification of the parasite in stool. Tests that detect antigens (proteins) to Giardia in the feces are especially useful for screening children in day-care settings, and for testing adults after treatment. Treatment may be with metronidazole (Flagyl). See also Giardia lamblia.