[Giardia] was first described in 1681 by a Dutch scientist, Antoni van Leeuwenhoek, and as such was the first pathogenic protozoan seen. It went unrecognized until 1859, when Dr. Vilem Dusan Fedorovic Lambl accidentally discovered the organism. Giardiasis was not effectively treated until 1937.
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.