LYCOS RETRIEVER 
Giardia: Environments
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Giardia'[S] main food source, glucose, is obtained by a process of diffusion or by pinocytosis. Like amoebae, they are aerotolerant anaerobes and require a reducing environment. Food reserves are stored in the form of glycogen. Glucose catabolism via the glycolytic pathway results in production of the end products ethanol, acetate and carbon dioxide.
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Consumption of just one cyst can cause disease, though the level of infectivity will vary among infected individuals and Giardia strains. The organism may exist in an actively reproducing form (trophozoite) or in a resting state or cyst. The cyst form has the ability to infect humans from environmental sources.
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Because clinical signs induced by Giardia spp. can be intermittent and since some Giardia spp. may be zoonotic, treatment of subclinically infected animals should be considered. However, since natural infection does not result in protective immunity, reinfection from the same contaminated environment is likely. In resistant or recurrent cases, consider other underlying disorders such as inflammatory bowel diseases, bacterial overgrowth, exocrine pancreatic insufficiency, and immunodeficiency. Since cyst shedding can be intermittent, it is difficult to use fecal flotation results to predict a cure.
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The researchers believe that the susceptibility of attached Giardia to tonicity changes can be traced to an unusual cellular structure on the parasite called the ventral disk. They believe it acts as a suction cup of sorts but with the "suction" created by osmotic pressure from a concentration imbalance between the outside environment and the fluid trapped beneath the ventral disk.
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