Giardia lamblia

Giardia duodenalis, also known as Giardia intestinalis and Giardia lamblia, is a flagellated parasitic protozoan microorganism of the genus Giardia that colonizes the small intestine, causing a diarrheal condition known as giardiasis. The parasite attaches to the intestinal epithelium by a ventral disc (syn. adhesive disc or sucker), and reproduces via binary fission. G. duodenalis is a non-invasive parasite, that does not spread to other parts of the gastrointestinal tract, but remains confined to the lumen of the small intestine. The parasite exists in two forms; trophozoites and cysts. The microorganism can undergo encystation, transforming into a dormant cyst that enables it to survive outside of its host. Giardia trophozoites are anaerobic, and absorb their nutrients from the intestinal lumen. If the organism is stained, its characteristic pattern resembles the familiar "smiley face" symbol. Chief pathways of human infection include ingestion of untreated drinking water (which is the most common method of transmission for this parasite), food, soil contaminated with human feces, and sewage, a phenomenon particularly common in many developing countries. Contamination of natural waters also occurs in watersheds where intensive grazing occurs. Giardia infections occur worldwide. It is the most commonly identified intestinal parasite among children in day-care centers, hikers and immunocompromised patients. About 20,000 cases per year in the United States are reported. Almost half of those infected with giardiasis remain asymptomatic. For those who do experience symptoms, they usually appear 1 to 2 weeks after infection. Common symptoms include abdominal pain, nausea, and bloating, along with large, watery, foul-smelling, and greasy stools. Due to frequent loose stools, individuals with giardiasis often experience dehydration. It has also been shown that G. intestinalis damages the intestinal epithelium, which directly affects nutrient absorption. In severe cases, giardiasis can lead to chronic diarrhea, chronic fatigue syndrome and cognitive impairment in children.