Giardia taxonomy, phylogeny and epidemiology: Facts and open questions

Giardia duodenalis (synonymous Giardia lamblia and Giardia intestinalis) is a flagellated protozoan parasite that reproduces in the small intestine causing giardiasis. It is a cosmopolitan pathogen with a very wide host range, including domestic and wild animal species, as well as human beings. In this paper the current knowledge about the taxonomy and phylogeny of G. duodenalis is summarized from the international literature and data on the detection and epidemiology are also reviewed concentrating on the last 20 years. Authors highlighted the current knowledge and some aspects on G. duodenalis in particular, water transmission and in vitro cultivation. The review sheds light on the difficulties of the strain differentiation and multilocus molecular analysis of Giardia strains especially when applied to water samples containing low numbers of cysts and components complicating the problem of tracking sources of contamination. Genetic elements determining or conferring traits such as infectivity, pathogenicity, virulence, and immune interaction contributing to clearance are currently not well established, if at all. These should be useful and important topics for future research.