The protozoan parasite Giardia intestinalis, also known as G. lamblia and G. duodenalis.
Infection usually occurs through ingestion of G. intestinalis cysts in water (including both unfiltered drinking-water and recreational waters) or food contaminated by the faeces of infected humans or animals.
Nature of the disease
Many infections are asymptomatic. When symptoms occur, they are mainly intestinal, characterized by chronic diarrhoea (watery initially, then loose greasy stools), abdominal cramps, bloating, fatigue and weight loss.
Risk for travellers
There is a significant risk for travellers in contact with recreational waters used by wildlife, with unfiltered water in swimming pools or with contaminated municipal water supplies.
Avoid eating uncooked food (especially raw fruit and vegetables) or ingesting any potentially contaminated (i.e. unfiltered) drinking-water or recreational water. Water can be purified by boiling for at least 5 min, or by filtration or chlorination, or by chemical treatment with hypochlorite or iodine (less reliable).