Symptoms of Giardia. Symptoms of Giardia: Introduction. The symptoms of Giardia infection can vary in intensity form person to person. Many people may have no symptoms at all. Giardia infection can result in the symptom of diarrhea that lasts ten days or more. Diarrhea may be explosive and very foul smelling. There may also be abdominal pain, nausea, vomiting, fever, chills, bloating, gas, and weight loss.