Giardia lamblia is a binucleated flagellated protozoan parasite that infects the small intestine. Infection typically results in chronic debilitating diarrhea, weight loss and malabsorption. Giardiasis may occur after drinking contaminated water.
Transmission also occurs by direct contact, especially with asymptomatic carriers and by food contamination. High risk categories include young children, immunocompromised patients, and those without previous exposure. More recently, giardiasis has been recognized as a sexually transmitted disease.