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  3. If you’ve kept up with the news lately, you’ve probably heard dire warnings about avian flu, or bird flu. It’s a highly infectio

If you’ve kept up with the news lately, you’ve probably heard dire warnings about avian flu, or bird flu. It’s a highly infectio

admin2010-10-14  34
问题     If you’ve kept up with the news lately, you’ve probably heard dire warnings about avian flu, or bird flu. It’s a highly infectious disease that has swept through the Asian bird population.  In October of 2005, the disease reached Eastern Europe, most likely through migratory birds. By January of 2006, several people in Turkey had contracted the disease. Although the virus does not infect humans easily, more than half of the people who have contracted it have died.
    But what exactly is bird flu? How is it different from the seasonal flu that people experience every year? How does it threaten people? What are governments doing to stop its spread?
Viruses and Influenza: An Overview
    A virus particle--or virion--is a microscopic packet that contains genetic material wrapped in a layer of protein. Some viruses also have a lipid membrane(脂质膜)around the protein coat. Unlike bacteria, they cannot reproduce on their own--they have to invade host cells. This process destroys cells and makes people sick.
    Viruses usually enter the bodies of animals and people through their mouths, mucus membranes or breaks in the skin. Then, they infect specific cells. For example, common cold viruses attack cells in the respiratory system. As they reproduce, they destroy their host cells, releasing copies of the virus to attack other cells. Some viruses are more stable than others, but in general they mutate frequently, sometimes making it difficult for doctors to treat them.
    Influenza is a specific type of virus that attacks the respiratory system. It can cause fevers, sore throats and congestion. If it attacks muscle cells, it can also cause muscle aches.
    There are three types of influenza virus--types A, B and C. Multiple subtypes exist within those types, and multiple strains(菌株)exist within each subtype. Like many viruses, influenza can mutate through antigenic drift(small changes that occur as it reproduces)or antigenic shift(major changes that create a new subtype of the virus).
Avian Flu
    According to the United States Center for Disease Control and Prevention( CDC), birds carry every known subtype of influenza A. When scientists talk about avian flu, however, they usually mean varieties that exist mostly or entirely in birds--not in people. Most of the time, birds can’t transmit the flu directly to people. They first infect pigs and other animals that can contract both human and avian flu strains. When the strains come into contact with one another, they create a new strain that infects humans.
    Many wild birds carry avian flu in their intestines(肠)and shed the virus in their droppings, but they don’t usually get sick from it. Domesticated birds, however, can get sick when they come into contact with contaminated(污染的)water, feed or soil. Birds spread the disease to each other through their saliva, respiratory secretions and droppings.
    Avian flu is either low pathogenic(致病的)or high pathogenic. Low pathogenic strains cause very mild symptoms, like ruffled feathers and reduced egg production. High pathogenic strains, however, can be deadly--they often have a mortality rate approaching 100%. Birds that survive can continue to shed the virus in their droppings for ten days after recovering, which helps the virus continue to spread.
Avian Flu H5N1
    In 1997, health officials in Hong Kong reported a virulent(致命的)strain of avian flu. For the first time, it appeared that the virus moved directly from birds to people instead of moving through a second species. The virus caused typical flu symptoms, and it also lead to eye infections, pneumonia and acute respiratory distress. Tests confirmed that this strain of the virus, influenza A H5N1, was completely new to humans.
    Eighteen people infected with the virus were hospitalized, and six of them died. The Hong Kong government, alarmed at the potential threat of a pandemic, took drastic steps. In about three days, the government destroyed about 1.5 million birds, Hong Kong’s entire poultry population. Although this measure sounds extreme, many health experts believe that Hong Kong’s actions prevented an influenza pandemic.
Avian Flu and a Global Pandemic
    Some people wonder whether scientists are overreacting to bird flu. After all, the virus has infected under 200 people, as compared to millions of birds. It also can’t easily move from birds to people, and it’s even less able to move from person to person. But public health officials have several concerns about avian flu:
    It has an extremely high mortality rate and kills previously healthy young adults.
    Since many wild, migrating birds carry it, controlling its spread is difficult.
    There’s no vaccine for the virus, which appears to be developing a resistance to the few drugs that can limit its severity.
    Right now, avian flu H5N1 is most threatening to birds, especially in Asia. The biggest threat to human health and potential for the spread of the disease is also in Asia, where many rural families have at least a few chickens that typically roam free instead of living in an enclosure.  But health officials report that the disease has gotten hardier and more infectious, and they worry that it may mutate and become a bigger threat to people.
    If the virus gained the ability to infect people more easily and to move from person to person, it could cause a pandemic--a global epidemic. Scientists warn that a flu pandemic is inevitable and that the world is unprepared for one. No one can predict when a pandemic might strike or whether influenza H5N1 will be the cause.
    Health officials in the United States, Europe and other Western countries are assisting Asian nations in managing avian flu. The steps that they’re taking to try to avoid a pandemic include:
    Containing or destroying any birds that appear to be infected.
    Advising people who handle poultry on proper hygiene and biosecurity practices. As more people contract the virus, it becomes more likely that disease will mutate into something more harmful to people.
    Administering seasonal flu vaccines to people who handle poultry. The flu shot doesn’t provide any protection against avian flu, but it does lower the likelihood that someone could be infected with both flu varieties at once, giving the viruses an opportunity to exchange genetic material.
    Monitoring wild and domestic birds for any signs of infection.
    Developing a vaccine for avian flu H5N1 , which German scientists say should be available in late 2005, and stockpiling antiviral drugs.
    Banning imports of birds and poultry and quarantining pets and performing animals when they return from countries with reported infections.
    Many countries also have plans in place for isolating infected travelers and quarantining anyone who has traveled with them. Response plans also outline how to limit the spread of the disease if a pandemic occurs.
According to CDC, birds carry every known subtype of influenza A and can transmit the flu directly to humans.
选项 A、Y
B、N
C、NG
答案B
解析 依据题干中的“CDC”，可将该题定位于第2副标题第1段。该段第1句提到“birds carry every known subtype of influenza A”，与题目的前半部分吻合；但后半部分“…can transmit the flu directly to humans”与第 3句“birds can’t transmit the flu directly to people”相悖。本题错误。
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