ABSTRACT
The parasitic flagellate Giardia intestinalis is one of the most frequently identified intestinal protozoan in humans. The primitive organization of the cell and some molecular similarity to bacteria suggests that the organism branched very early in the evolution. The parasite is distributed worldwide. Giardiasis, endemic in developing countries, appears repeatedly as a water-borne epidemic in the industrialized world. Relatively harmless and self-limited disease in immunocompetent adults may present as persistent and devastating diarrhoea in malnourished children. Morphologically identical parasites exist in several wild and domestic animals. Their role in the transmission of human disease is not sufficiently proven. Despite the over 300-year-old medical history, the progress in the research and understanding of the biology of the parasite and the pathogenesis of the disease has been relatively slow. Giardia and giardiasis are still subjected to controversial opinions concerning the zoonotic nature, interspecies transmission, host specificity, and taxonomy of the parasite.
