what causes giardiasis
1 Giardiasis is the name of the disease caused by Giardia lamblia parasites that infect the small bowel.2  Giardiasis is caused by Giardialamblia parasites that damage the small intestine; Giardia lamblia forms cysts are transmitted to humans in contaminated water or food and by person-to-person contact. Giardiasis is the name of the disease caused by Giardia lamblia parasites that infect the small bowel.