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A 体裁 议论文 话题 禽流感的防治 词数 373 Tiredness, coughing, a runny nose and a sore throat—among all sicknesses there is probably none more common than the flu, which we all get now and then. However, bird flu is a completely different story. Ten years ago, the H5N1 bird flu swept across 15 countries, including China, with sufferers reporting chest pain, difficulty breathing, fever and severe coughing. More than 600 people were infected, and about 60 percent died. Now another type of bird flu hit Shanghai and three neighboring provinces, and this time the virus is called H7N9. By the afternoon of April 11, the new virus had taken nine lives out of 35 infected, according to Xinhua News Agency. The “H” and “N” in the virus’ name refers to two kinds of proteins on the surface of the virus. Any change of the numbers of the two proteins indicates a new mutation (变异) . Most of the mutations only affect birds, such as chickens and pigeons, and don’t normally spread to humans. But once they do, the results can be disastrous. “Any time an animal influenza virus crosses to humans, it is a cause for concern, ”Malik Peiris, virologist (病毒学家) at the University of Hong Kong, told Nature magazine. Take the SARS epidemic (传染病) 10 years ago as an example. The virus behind the disease is thought to have jumped to humans from animals. The virus was a complete “stranger” to human bodies, which hadn’t developed an immunity against it. | 
