Interaction of Giardia with Host Cells

In the context of host-Giardia interaction, adhesion of parasites to epithelial cells is considered the initial event that allows establishment of the parasite in the host. During this contact trophozoites also interact with microenvironmental factors to indirectly promote pathophysiologic alterations in the infected host contributing to some extent to the variable clinical outcome of giardiasis. Giardia contains a unique key element, the adhesive disk which is involved in adhesion of Giardia to host cells. This structure together with other specialized parasite elements that include the ventrolateral flange, the flagella, and several parasite molecules located at the intracellular (contractile proteins), epicellular (i.e. cell surface molecules) levels or secreted participate in the colonization of the very hostile environment at the small intestine. Several observations have indicated that trophozoites secrete various molecules that upon interaction with epithelial cells may be responsible for the pathologic changes seen at the enterocyte during the course of giardiasis. Also due to this interaction, alterations related to the transport of a variety of solutes such as chloride and sodium ions as well as high sized proteins have been documented. Moreover changes occur in the arrangement of α-actinin, myosin light chain, F-actin related to cytoskeleton dynamics and of proteins that participate in the intercellular junctions such as claudins and ZO-1 which in turn may lead to the activation of apoptotic signaling. All these manifestations may be related to the parasite strain and are also influenced by the immune, clinical, and nutritional status of the host leading to the onset of giardiasis.