Giardiasis is an intestinal infection caused by the zoonotic protozoan parasite Giardia intestinalis (previously G. lamblia). Giardia cysts shed in animal or human feces may contaminate food or drinking water or be transferred on hands or fomites; recreational waters such as lakes and pools may also serve as vehicles of transmission. Incubation can range from 3–25 days or longer, but the median incubation time is 7–10 days. While usually asymptomatic, symptoms can include sulfurous burps, chronic diarrhea, frequent loose and pale greasy stools, bloating, cramps, fatigue, and weight loss. Complications are rare, but may include malabsorption of fats and fatsoluble vitamins. Children in day care represent a reservoir of disease in developed countries. There is no vaccine.
CDC: Giardia http://www.cdc.gov/parasites/giardia/
Giardia Fact Sheet http://www.cdph.ca.gov/HealthInfo/discond/Documents/GiardiasisFactSheet.pdf