infectious diseases
Giardiasis
Introduction
Giardiasis is infection with the flagellated protozoanGiardia duodenalis(G. lamblia,G. intestinalis). Infection can be asymptomatic or cause symptoms ranging from intermittent flatulence to chronic malabsorption. Diagnosis is by identifying the organism in fresh stool or duodenal contents, by assays forGiardiaantigen, or molecular testing for parasite DNA in stool. Treatment is withmetronidazole,tinidazole, ornitazoxanideor, during pregnancy,paromomycin. (See also Overview of Intestinal Protozoan and Microsporidia Infections .) Giardiatrophozoites firmly attach to the duodenal and proximal jejunal mucosa and multiply by binary fission. Some organisms transform into environmentally resistant cysts that are spread by the fecal-oral route. Giardia infection is prevalent throughout the world, particularly in areas with poor sanitation. Giardiasis is the most common intestinal parasitic disease in the US. Waterborne transmission is the major source of infection ( General reference ), but transmission can also occur by ingestion of contaminated food or by direct person-to-person contact. Giardiacysts remain viable in surface water and are resistant to routine levels of chlorination in drinking water. Thus, mountain streams as well as chlorinated but poorly filtered municipal water supply systems have been implicated in waterborne epidemics. Infections are also associated with childcare, especially involving diaper-aged children; close contact with family or household members who have giardiasis; ingestion of water or ice from untreated or improperly treated water from lakes, streams, or wells; backpackers, hikers, and campers who drink unsafe water or fail to practice good hand hygiene; ingesting water while swimming or playing in lakes, ponds, rivers, or streams; or exposure to feces through sexual contact. There are 8 genetic groups (assemblages) ofG. duodenalis. Two infect humans and animals; the others infect only animals. The clinical manifestations appear to vary with genotype. 