Light microscopy of the parasitic protozoan Giardia lamblia, cause of giardiasis. Giardiasis is a form of gastroenteritis, causing diarrhoea, stomach cramps and excessive gas production. It is usually contracted through drinking contaminated water. Giardia lamblia is found in water throughout the world, surviving as a hardy cyst. When ingested by a human or other animal, the cyst travels to the small intestine, where it develops into the active form seen here. This form attaches to the intestinal wall, feeding and reproducing, and producing more cysts that are passed in faeces. The disease is usually self-limiting, but it can be treated with drugs such as metronidazole.