Giardia intestinalis (syn. lamblia, duodenalis) is the most common human protozoan enteropathogen and there is now compelling evidence to indicate that infection with this parasite can cause both acute and chronic diarrhoea.^[53] Intestinal malabsorption may be severe, such that chronic infection in children may be associated with retardation of growth and development. Molecular and genetic analysis of the parasite has shown that Giardia has a unique place in evolution as it is probably the first organism to emerge from the prokaryotic to the eukaryotic state.^[54]Our knowledge of this parasite has expanded rapidly since it was first cultured in the 1970s, but many aspects of its biology and interactions with its mammalian hosts remain unanswered. There is no unifying explanation for the diverse clinical spectrum seen in giardiasis, which ranges from asymptomatic carriage to persistent diarrhoea with malabsorption. As yet, no classical virulence …