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Excerpt:
Microbes are constantly on the move. Those present in animals occasionally breach the species barrier, infecting humans who are in close contact. Once microbes have successfully emerged in humans, the infection they cause may be asymptomatic or may show signs and symptoms of disease.
Influenza viruses are one such family of microbes. Most are thought to have their origin in water fowl. The influenza A (H5N1) virus (also know as the avian flu virus or simply H5N1) circulates among chickens, in some parts of the world and occasionally infects humans with a severe and fatal disease. At present, the H5N1 virus rarely passes from one human to another, thought a mutation at any time could result in a pandemic - an epidemic that occurs successively or simultaneously in all parts of the world.
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