Giardia lamblia
- The trophozoite form of Giardia lamblia was first observed in 1681 by Antonie van Leeuwenhoek in his own diarrhea stools. The organism was again observed and described in greater detail by Vilém Du?an Lambl in 1859, who thought the organism belonged to the genus Cercomonas and proposed the name Cercomonas intestinalis. His name is still sometimes attached to the genus or the species infecting humans. Thereafter, some have named the genus after him while others have named the species of the human form after him Giardia lamblia.
- The names for the human parasite Giardia duodenalis, Giardia lamblia and Giardia intestinalis are all in common current use despite the potential for confusion that this has created.
-Giardia lamblia is a flagellated protozoan parasite that colonises and reproduces in the small intestine, causing giardiasis. The giardia parasite attaches to the epithelium by a ventral adhesive disc(sucking disc), and reproduces via binary fission. Giardiasis does not spread via the bloodstream, nor does it spread to other parts of the gastro-intestinal tract, but remains confined to the lumen of the small intestine. Giardia trophozoites absorb their nutrients from the lumen of the small intestine, and are anaerobes. If the organism is split and stained, it has a very characteristic pattern that resembles a familiar "smiley face" symbol.
-Giardia infects humans, but is also one of the most common parasites infecting cats, dogs and birds. Mammalian hosts also include cows, beavers, deer, and sheep.
-Giardiasis occurs where there is inadequate sanitation or inadequate treatment of drinking water. Giardiasis is one of the causes of "travelers diarrhea" that occurs during travel to less-developed countries
-Life cycle
Giardia infection can occur through ingestion of dormant cysts in contaminated water, food, or by the faecal-oral route (through poor hygiene practices). The Giardia cyst can survive for weeks to months in warm water, and therefore can be present in contaminated wells and water systems, especially stagnant water sources such as naturally occurring ponds, storm water storage systems, and even clean-looking mountain streams. They may also occur in city reservoirs and persist after water treatment, as the Giardia cysts are resistant to conventional water treatment methods such as chlorination and ozonolysis. Zoonotic transmission is also possible, and therefore Giardia infection is a concern for people camping in the wilderness or swimming in contaminated streams or lakes, especially the artificial lakes formed by beaver dams (hence the popular name for giardiasis, "Beaver Fever").
In addition to waterborne sources, faecal-oral transmission can also occur, Not all Giardia infections are symptomatic, and many people can unknowingly serve as carriers of the parasite.
The life cycle begins with a noninfective cyst being excreted with the faeces of an infected individual. The cyst is hardy, providing protection from various degrees of heat and cold, desiccation, and infection from other organisms. A distinguishing characteristic of the cyst is four nuclei and a retracted cytoplasm. Once ingested by a host, the trophozoite emerges to an active state of feeding and motility. After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission. The resulting trophozoites and cysts then pass through the digestive system in the faeces. While the trophozoites may be found in the faeces, only the cysts are capable of surviving outside of the host.
Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance. Cysts are distinguished by a retracted cytoplasm. This protozoan lacks mitochondria, although the discovery of the presence of mitochodrial remnants organelles .
life cycle of Giardia lamblia
-clinical symptoms
Symptoms of infection include diarrhea, malaise, excessive gas (often flatulence or a foul or sulphuric-tasting belch, which has been known to be so nauseating in taste that it can cause the infected person to vomit), steatorrhoea (pale, foul smelling, greasy stools), epigastric pain, bloating, nausea, diminished interest in food, possible (but rare) vomiting which is often violent, and weight loss. Pus, mucus and blood are not commonly present in the stool. It usually causes "explosive diarrhea" and while unpleasant, is not fatal. In healthy individuals, the condition is usually self-limiting, although the infection can be prolonged in patients who are immunocompromised, or who have decreased gastric acid secretion.People with recurring Giardia infections, particularly those with a lack of IgA, may develop chronic disease.Vitamin B12 deficiency,hypoproteinemia, hypogammaglobinemia, folic acid deficiency, stractural changes of the intestinal villi. Lactase deficiency may develop in an infection with Giardia,
Treatment and diagnosis
Giardia lamblia infection in humans is frequently misdiagnosed. Accurate diagnosis requires an antigen test or, if that is unavailable, an ova and parasite examination of stool. Multiple stool examinations are recommended, since the cysts and trophozoites are not shed consistently.,its important to note that giardia is often shed in the stool in (showres) ; meaning that many organisms may be passed and recoverd on one days sample and the following days sample may reveal no parasite at all. some patients should be treated on the basis of empirical evidence; treating based on symptoms. In addition duodenal contents obtained by aspiration, string test or enterotest technique is also used for diagnosis giardia and ELIZA test.
Human infection is conventionally treated with metronidazole, tinidazole or nitazoxanide. Although Metronidazole is the current first-line therapy,
Multiple protease activities in Giardia intestinalis trophozoites