Profuse watery diarrhoea in an immune compromised child is due to

Giardiasis caused by Giardia lamblia is a major cause of diarrhoea in children and travellers. Individuals with malnutrition,humoral immunodefeciencies,and cystic fibrosis are particularly susceptible. Features: acute diarrhoea with sudden onset of explosive, watery foul smelling stools, along with nausea and anorexia,abdominal distension,flatulence,epigastric camps and mild fever.