Giardia lamblia

This chapter discusses several aspects of the biology of Giardia and the pathology associated with infection while highlighting the laboratory models currently used to study this parasite. Historically, Giardia lamblia was so common that it was once considered a commensal organism of the human intestine. The life cycle of Giardia lamblia includes an infectious cyst form and a noninfectious, rapidly multiplying trophozoite form. Diagnosis of infection in both humans and animals is predominately based on microscopic identification of Giardia cysts in fecal samples, although in recent years, enzyme-linked immunosorbent assay (ELISA)- and polymerase chain reaction (PCR)-based techniques have been developed. Giardia lamblia morphology is drawn from studies utilizing electron microscopy to visualize the surface, cytoskeletal, and intracellular components of the parasite. Much of the work on Giardia lamblia encystation has been done by in vitro manipulation of axenically cultured trophozoites.