Giardia

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Giardia or Giardiasis
What is the infectious agent (pathogen) that causes this infectious disease? For example, the name of the bacteria, virus, or parasite. Giardia is a flagellated (meaning to have whip-like appendages for movement) protozoan that attaches itself to the lining of the upper intestinal tract of a host animal. Giardia lamlia is the parasite also known as G. intestinalis or G. duodenalis and was first observed by Anton van Leeuwenhoek in 1681. Anton van Leeuwenhoek also invented the microscope. It was named in 1915 for the two scientists who studied it: Prof. A. Giard in Paris and Dr. F. Lambl in Prague. There are species of Giardia other than Giardia lamblia that infect small rodents, amphibians, birds, and fish, but are not passed on to humans. Once Giardia attaches itself to the lining of the intestine it begins to feed and reproduce, causing Giardiasis (the infection). Giardia is a trophozoite that reproduces by dividing itself, which is called binary fission, about every 12 hours. One single parasite can theoretically result in more than a million in 10 days and a billion in 15 days. At some time, it releases its hold on the intestine and travels in the fecal stream. The trophozoite then transforms into an egg-like structure called a cyst and eventually passed in the stool. This cyst excretion is called shedding and can last for months. Once outside the body the cyst is ingested by another animal. Stomach acid and digestive enzymes cause the cyst to “hatch” into trophozoites and the cycle repeats. How is this infectious agent transmitted through food or water? Infected people and animals pass Giardia cysts in their stool. The cysts can survive in the environment in water and food, and on surfaces and objects. People get Giardiasis by ingesting the infectious stage (cysts) of the parasite. This can happen by swallowing water from a swimming pool, lake, river, pond, or stream contaminated with sewage from Giardia-infected people or animals....
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