Giardiasis is an infectious disease of the small bowel caused by a protozoan parasite of the genus Giardia. Symptoms range through diarrhoea, weakness, weight loss, abdominal cramps, nausea, greasy stools, abdominal distension, flatulence, vomiting, belching and fever. As well as intestinal disorders, there might be severe malnutrition and problems with the bile ducts and gall-bladder or even the pancreas.
As a faecal infection, giardiasis spreads from person to person, particularly in families and amongst those living in close-knit environments. It is also transmitted from animals to humans. Most strains of Giardia prefer one host, with one major exception, which enables cross-species infection.
Giardia are not affected by chlorination and remain viable in water for a long time.
Giardiasis has worldwide distribution. Persons of all ages are affected, but occurrence is especially high among children and among the poor. This parasitic infection is considered the most common intestinal syndrome in the United States and Europe. Giardiasis may affect two percent of the population in Europe and up to 20% in some tropical countries. It is a common cause of travellers' diarrhoea, especially when visiting St. Petersburg in Russia, the Middle East and India.