Giardia and Giardiasis

This chapter provides an overview of Giardia and giardiasis. General morphology of the trophozoite of Giardia duodenalis is shown diagrammatically. Scanning electron microscopy (SEM) has provided considerable information about the surface structure of Giardia, particularly in relation to the ventral (attachment) disc. The cytoskeleton, internal organization, and endosymbionts of Giardia are also reviewed. Considerable genetic variation occurs in Giardia, particularly in G. duodenalis. The nature of differences found between the isolates of G. duodenalis may have a significant influence on the epidemiology and control of giardiasis, particularly differences in host specificity, growth and development, virulence, drug sensitivity, and antigenicity. Much of this variation has a genetic basis and the extent of this variation indicates the existence of a number of species within the G. duodenalis morphological group. The life cycle and laboratory maintenance of Giardia is described. Giardia has a simple direct life cycle. Attachment is an essential feature of the relationship between Giardia and its host, and the ability to attach in vitro is an important indicator of viability.