Abstract

Giardia lamblia is a protozoan parasite that inhabits the upper small intestine of humans and several other vertebrates and one of the most frequent cause of intestinal disease worldwide. During its life cycle, G. lamblia undergoes significant biochemical and morphological changes that allow the parasite to survive under hostile environmental conditions. To survive outside the host's intestine, Giardia differentiates into resistant cysts, which are characterized by a rigid extracellular cyst wall that protect the parasite even to the action of the most common chemical disinfectants. Another adaptive mechanism of Giardia is the switching of its surface antigens, a mechanism that allows the trophozoites to evade the host's immune responses and produce acute, chronic and/or recurrent infections. During the last years, important advances in the knowledge of the molecular basis underlying the mechanisms of encystation and antigenic variation in Giardia suggest that novel chemotherapeutic and/or immunoprophylactic reagents against this important human pathogen could soon be available.