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感冒易发的季节来临之际：我们需要了解什么是流感
译文：
流行感冒是一种常见的传染病，病变的部位在鼻子和咽喉，有时是肺。流感病毒在人与人之间传染。感染的人呼气时把病毒散布在空气之中。
病毒进入鼻子或口腔之后人就会患流感。症状表现在肌肉疼痛，突然高烧，呼吸困难和浑身乏力。通常情况下，大多数人会在一两周之后感觉好些，但是这种病能够致命。尤其是儿童和老年人，还有身体虚弱的人。
世界卫生组织表示，每年在全世界范围内有500万人感染流感病毒，每年死于流感的人数在250,000到500,000之间。
有时，医疗专家们能够在冬季诊断出流感，但是一直不清楚致病原因。
美国研究人员现在终于了解流感病毒为什么在冬季传播而不是夏季，那是因为这种病毒在寒冷而干燥的空气中生存的时间更长。
纽约的研究人员在动物身上进行了20次试验，目的是调查病毒是如何传播的。首先，他们找来可以感染并传播流感病毒的豚鼠。然后把它们放进空气中布满流感病毒的地方，改变空气的温度和温度。
人们发现在温度为5℃和湿度为20%时，流感病毒最为活跃。温度升高以后，只有少数几只豚鼠患了流感。温度在30℃和湿度在80%的时候病毒完全停止活动。同时发现温度很低的时候，病毒在动物们之间传播的时候长达两天之久。
研究成果发表在公共科学图书馆的出版物《病源杂志》上。
论文表示，寒冷的天气里人们在室外行走时，比在暖室里更易感染流感。冷空气是病毒生存的条件，而干燥的空气可以令其停留得更久。这是因为，病毒粒子粘附在悬浮在空中的极其微小的水滴上，当空气非常潮湿时，这些小水滴就会更加迅速落在地面上。
不过，研究人员说，人们不应该总是在寒冷的天气里呆在温暖的室内以避免患上流感。最好的预防是每年注射一次疫苗。
医学专家们已经确认出三类流行感冒，分别是A型，B型和C型。C型症状最轻，不易察觉。不过其他两种非常相似。病毒为了生存会发生变异，使得人体在识别并抵抗疾病时困难重重。
一个人在患了其中一种流感之后，不可能再次患上同类型的感冒。人体的免疫系统产生抗体。这种物质停留在血液里，破坏再次出现的病毒。不过，一旦病毒发生，哪怕是一个很小的变化之后，抗体可能失去作用。
每年，研究人员都要发明新的流感疫苗。世界卫生组织主持会议，专家们讨论下一种疫苗所要对抗的流感病毒的类型。
有关流感的历史记载可追溯到两千多年以前。罗马史学家李维记载过有类似的疾病突袭罗马军队。15世纪的意大利人以为这种病是星星的作用力（influence）所致，称它为“流行感冒”（influenza）.
1781年，流感从欧洲传到北美，西印度群岛和拉丁美洲。1829年这种感冒在亚洲流行，并在1836年再次流行。同时传播到东南亚，俄罗斯和美国。
1889年，流感再次出现在中亚，向北进入俄罗斯，向东进入中国，向西进入欧洲。后来，北美和非洲的人也感染流感。专家们认为在欧洲有250,000人死于这次流感大暴发，全世界范围内至少有一百万。
历史上最可怕的流感大爆发就是首先出现在西班牙的那次。1918年和1919年，西班牙流感在全世界夺去两千万到五千万人的生命。即使年轻力壮的人也不能幸免——染病后几天就死去。
流感传播期间为被为“大爆发”。世界卫生组织认为下一次流感大爆发可能会在工业国家里导致65万人丧生，但是更为严重的情况会出现在发展中国家。这些国家的医疗资源有限，人们因健康状况恶劣和饮食差而容易受到病毒攻击。
研究人员表示新型流感病毒的出现将无法预测。他们没有足够的时间辨别并生产相应的疫苗。正因为如此，人们正在寻找能够更快的生产疫苗的方法。
80年前，流感病毒散布到全世界需要花上几个月的时间。现在通过飞机只需要几天就够了。
世界卫生组织在去年表示，现在比1968年以来的任何时间都更易发生流感大爆发。病毒会以更快的速度在许多国家袭击大量的人群。H－5 N－1型流感病毒是造成大爆发的一个重要隐患，也就是俗称的“禽流感”。
野生和农场禽类经常携带病毒，不过通常没有感染。1997年，6个香港人死于H－5 N－1型禽流感。由于香港政府迅速下令扑杀所有农场禽类，避免了这种病毒向人类大规模传播。
但是，这种病毒已经传播到亚洲其他地区。2003年到2006年间，有16个国家发现了这种病毒。
WHO透露，截止12月12日，感染禽流感的总人数达到338人。其中208人死亡。不过，去年感染和死于禽流感的人数少于2006年。
这些数据说明致命的禽流感病毒在人类之间的传播并不容易。但是，这个情况可能会改变。研究人员担心病毒一旦变异就会在人与人之间传播。人们感染上之前从未接触过的病毒之后就会不堪一击。
研究人员正在尝试寻找预防禽流感的疫苗。不过，在一场大爆发到来之前，是不会有疫苗出现的。
一些英国研究人员提醒人们通过物体屏障预防流行性疾病，如口罩或手套。人们查看了51篇已发表的论文，这些论文的内容全是有关保护咽喉和肺部不受感染的简单方法的使用效果。人们发现勤洗手，戴口罩和手套都能够阻止传播病毒。如果几个物体屏障同时使用效果更明显。这些简易的，廉价的措施证明预防致命病毒的散布并非难事。
原文：
Influenza is a common infection of the nose and throat, and sometimes the lungs. The cause is a virus that passes from one person to another. The virus spreads through the air when an infected person expels air suddenly.
Influenza develops after the virus enters a person's nose or mouth. The flu causes muscle pain, sudden high body temperature, breathing problems and weakness. Generally, most people feel better after a week or two. But the flu can kill. It is especially dangerous to the very young, the very old and those with weakened defenses against disease.
The World Health Organization says the influenza virus infects up to five million people around the world each year. Between two hundred fifty thousand and five hundred thousand people die every year from influenza.
Medical experts have recognized for some time that people become infected with influenza during the winter months. But they did not really know why until recently.
American researchers say they now know why the influenza virus spreads in the winter and not in the summer. They say it is because the virus remains in the air longer when the air is cold and dry.
Researchers in New York carried out twenty experiments with guinea pigs to investigate how the virus spreads. First, they confirmed that the guinea pigs could develop the flu and pass it on to others. The researchers then placed the animals in areas where the virus was present in the air. Then they changed the temperature and humidity levels of their environments. Humidity is the amount of wetness in the air.
The researchers found the virus spread the most when the temperature was about five degrees Celsius and the humidity was twenty percent. Few of the guinea pigs developed influenza as the temperature increased. The virus stopped spreading completely at thirty degrees Celsius and eighty percent humidity. The researchers also found that the animals spread the virus among themselves nearly two days longer when the temperature was low.
Results of the study were reported in PLoS Pathogens, a publication of the Public Library of Science.
One of the researchers said the study shows that influenza virus is more likely to infect people during an outdoor walk on a cold day than in a warm room. He said cold air helps the virus survive in the air and low humidity helps it stay there longer. That is because particles of the virus ride on the extremely small drops of water floating in the air. When the air is very humid, water droplets fall to the ground more quickly.
The researchers say, however, that people should not stay in warm places all the time in cold weather to avoid the flu. They say the best way to prevent the sickness is to get yearly injections of a vaccine that prevents influenza.
Medical experts have identified three major kinds of influenza. They call them type A, B and C. Type C is the least serious. People may not even know they have it. But researchers study the other two kinds very closely. Viruses change to survive. This can make it difficult for the body to recognize and fight an infection.
A person who has suffered one kind of flu cannot develop that same kind again. The body's defense system produces antibodies. These substances stay in the blood and destroy the virus if it appears again. But the body may not recognize a flu virus that has even a small change.
Each year, researchers develop vaccines to prevent the spread of the flu virus. The World Health Organization holds meetings in which experts discuss what kinds of flu viruses to include in the next vaccine.
Historical records have described sicknesses believed to be influenza for more than two thousand years. The Roman historian Livy described such a disease attacking the Roman army. People in fifteenth century Italy thought sicknesses were caused by the influence of the stars. So they called it, "influenza."
In seventeen eighty-one, influenza moved from Europe to North America to the West Indies and Latin America. The flu spread in Asia in eighteen twenty-nine, then again in eighteen thirty-six. It also traveled to Southeast Asia, Russia and the United States.
In eighteen eighty-nine, the flu began in Central Asia, spread north into Russia, east to China and west to Europe. Later, it affected people in North America and Africa. Experts say two hundred fifty thousand people died in Europe in that flu pandemic. Around the world, the number was at least one million.
The deadliest spread of influenza ever reported involved a flu that first appeared in Spain. The Spanish flu killed between twenty million and fifty million people around the world in nineteen-eighteen and nineteen-nineteen. Even young, healthy people became sick and died in just a few days.
Periods when diseases spread around the world are called pandemics. The World Health Organization says the next flu pandemic is likely to kill as many as six hundred fifty thousand people in industrial countries. But it says the greatest effect will likely be in developing countries. The W.H.O. notes that health resources in those countries are limited, and people there are weakened by poor health and diet.
Researchers say the new kind of flu will appear unexpectedly. They will not have enough time to identify it and produce a vaccine. That is why they are developing faster ways to produce vaccines.
Eighty years ago, the flu virus took months to spread around the world. Today, airplane travel means a virus can spread to far around the world in just days.
Last year, the World Health Organization said the world is closer to a pandemic of the influenza virus than at any time since nineteen sixty-eight. The flu virus would spread quickly to large numbers of people in many countries. The pandemic threat is the h-five n-one influenza virus, also known as the bird flu.
Wild and farm birds often have a flu virus. Yet they usually are able to carry the virus without getting sick. In nineteen ninety-seven, six people in Hong Kong died of the h-five n-one virus. The Hong Kong government quickly ordered the killing of all farm birds there. That stopped the spread of h-five n-one to people in Hong Kong.
Yet the virus had already spread to other parts of Asia. It was found in sixteen countries between two thousand three and two thousand six.
The WHO says the bird flu virus had infected a total of three hundred thirty-eight people by December twelfth. Two hundred eight of them died. Yet fewer people were infected with bird flu or died of it last year than in two thousand six.
These numbers show that the deadly bird flu virus is not spreading among people very easily. But that could change. Researchers are worried about the virus changing so that it could spread from person to person. People would become infected with a virus their bodies have never before experienced. They would have no protection.
Researchers are attempting to develop a vaccine to protect against bird flu. Still, they know that any vaccine would not be ready until a pandemic had already begun.
Some British researchers say people should be told to wear physical barriers against infectious diseases, like masks on the face or gloves to protect the hands. The researchers examined fifty-one published studies on the effect of simple ways to prevent throat and lung infections. They found that hand-washing, wearing masks and using gloves each stopped the spread of viruses. The researchers also found that such physical barriers were even more effective when used together. They said these simple, low-cost measures could prove to be an easy way to prevent the spread of deadly viruses.
[精彩文摘]流感时期话流感