ABSTRACT
Members of the genus Giardia are ubiquitous flagellated protozoa that infect the intestinal tracts of a wide range of vertebrates including mammals, amphibians, and birds. Among them, G. duodenalis is the etiological agent of giardiasis, a major cause of gastrointestinal illness estimated to affect about 200 million people each year only in developing countries. 1 Although not formally considered a neglected tropical disease, giardiasis belongs to the group of poverty-related infectious diseases that impair the development and socioeconomic potential of infected individuals in endemic areas. G. duodenalis is also a significant contributor to the burden of diarrheal disease in developed countries. 2 The infection is transmitted via the fecal-oral route after ingestion of cysts either indirectly through contaminated water, food, or fomites, or directly through contact with infected individuals or animals. Host (age, immune status, concomitant intestinal microbiota, and diet) and parasite (genotype, virulence, resistance to chemotherapy, and ability to evade immune response) determinants will define the outcome of the infection, whose clinical manifestations range from asymptomatic carriage, self-limited acute diarrhea, and chronic infection. 3 In recent years, molecular methods including polymerase chain reaction (PCR)–based assays, sequencing, and phylogenetic analyses have made a substantial contribution to our understanding not only of the epidemiology, but also the taxonomy, evolutionary history, diagnostics, and pathogenesis of G. duodenalis. In this chapter, we present a state-of-the-art review of recent advances, and remaining challenges in the field of human giardiasis under a public health perspective.
