Some people with giardia infection never develop signs or symptoms but still carry the parasite and can spread it to others through their stool. For those who do get sick, signs and symptoms usually appear one to three weeks after exposure and may include: 1  Watery, sometimes foul-smelling diarrhea that may alternate with soft, greasy stools. 2  Fatigue or malaise. 3  Abdominal cramps and bloating.  Gas or 1  flatulence. Nausea.  Weight loss.