Definition
Giardia lamblia is a flagellated protozoan parasite that colonizes the small intestine of humans and other mammals, causing the gastrointestinal disease giardiasis. The organism is characterized by a pear-shaped trophozoite with two nuclei and a ventral adhesive disc.
Explanation
Giardia lamblia belongs to the diplomonad group of protozoa and has a simple life cycle consisting of two stages: a trophozoite that multiplies in the upper small intestine and a hardy cyst that is excreted in feces. Transmission occurs through ingestion of cysts in contaminated water, food or by direct fecal-oral contact. After excystation in the duodenum, trophozoites attach to the epithelium using their adhesive disc, interfering with nutrient absorption and causing symptoms such as diarrhea, abdominal cramps and weight loss. Giardia lacks mitochondria and many typical eukaryotic organelles, relying on anaerobic metabolism. Infection is common worldwide, particularly in areas with inadequate sanitation. Diagnosis is made by detecting cysts or trophozoites in stool samples or by antigen detection assays, and treatment typically involves nitroimidazole drugs such as metronidazole or tinidazole. Immunity to infection is not complete, and reinfection can occur.
Notable examples and facts
Giardia lamblia infections are particularly prevalent among travellers, campers and children in daycare settings who consume untreated water. The cysts are environmentally resistant and can survive for months in cold water, making chlorination alone insufficient for elimination. In addition to infecting humans, Giardia infects a wide range of mammals including dogs, beavers and livestock. Outbreaks have been linked to recreational water parks and municipal water systems that were not adequately filtered. Laboratory identification of cysts with characteristic four nuclei and internal fibrils provides a rapid diagnosis. Vaccine development is ongoing but none are currently available.
Giardia lamblia remains a significant cause of waterborne diarrhea worldwide. Control relies on improved sanitation, safe drinking water and appropriate chemotherapeutic regimens.
Related Terms: Protozoa, Trophozoite, Cyst, Giardiasis, Intestinal parasite