Giardiasis is an infectious disease spread by the parasite Giardia that affects the stomach and bowels, and is a common cause of diarrhea. The disease is spread when people swallow food or water that has been contaminated by the parasite. Giardiasis is commonly spread when people do not wash their hands with soap and water or change a diaper and then later eat, smoke, or touch other things. Giardiasis can also be spread by animals. Symptoms of giardiasis include diarrhea, abdominal cramps, bloating, increased gas, weakness, loss of appetite, weight loss, and foul-smelling soft stools. These symptoms generally appear seven to ten days after infection. There are several medications available to treat giardiasis.