ABSTRACT
The protozoan agellate Giardia duodenalis is the etiological agent of giardiasis, one of the commonest gastrointestinal infections of mammals, including humans, with a worldwide distribution. The infection is transmitted by the fecal-oral route through ingestion of cysts, by both direct and indirect routes. In humans, infection is caused by two genetically distinct groups of G. duodenalis, namely, assemblages A and B, whereas the remaining six assemblages (C through H) described to date infect other mammals, with various degrees of host specicity. Humans acquire infections mostly by consumption of contaminated water, and the numerous outbreaks reported further underline the important role that water plays in the transmission of Giardia. In comparison, less is known about foodborne giardiasis, due to the difculties in investigation of cases and to the lack of standard methods for the detection of Giardia on foodstuffs. Clinical giardiasis occurs only in a percentage of infected individuals, whereas many cases are asymptomatic, but the reasons for this variability in clinical presentation are unknown. In recent years, important progress has been made in understanding the taxonomy, genetics, epidemiology, and pathogenesis of this organism. This chapter highlights relevant advances in these elds.
