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  3. Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that

Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that

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问题     Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that have undergone no sig- nificant genetic change. In analyzing the latter, scientists have discovered the importance of social and ecological factors to epidemics. Poliomyelitis, for example, emerged as an epidemic in the United States in the twentieth century; by then, modern sanitation was able to delay exposure to polio until adolescence or adulthood, at which time polio infection produced paralysis. Previously, in- fection had occurred during infancy, when it typically provided lifelong immunity without paralysis. Thus, the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic po- lio epidemic. Another example is Lyme disease, which is caused by bacteria that are transmitted by deer ticks. It occurred only sporadically during the late nineteenth century but has recently be- come prevalent in parts of the United States, largely due to an increase in the deer population that occurred simultaneously with the growth of the suburbs and increased outdoor recreational activ- ities in the deer’s habitat. Similarly, an outbreak of dengue hemorrhagic fever became an epidemic in Asia in the 1950’s because of ecological changes that caused Aedes aegypti, the mosquito that transmits the dengue virus, to proliferate. The stage is now set in the United States for a dengue epidemic because of the inadvertent introduction and wide dissemination of another mosquito, Aedes albopictus.
Which of the following can most reasonably be concluded about the mosquito Aedes albopictus on the basis of information given in the passage?
选项 A、It is native to the United States.
B、It can proliferate only in Asia.
C、It transmits the dengue virus.
D、It caused an epidemic of dengue hemorrhagic fever in the 1950’s.
E、It replaced Aedes aegypti in Asia when ecological changes altered Aedes aegypti’s habitat.
答案C
解析 哪一个是文中给出的关于自纹伊蚊(Aedes albopictus)的信息?A．美国土生。说反了。L38，inadvertent introduction。B．只在亚洲繁殖。原文指出在美国“wide dissemination”。C．正确。传播登革热。原文最后指出它在美国传播登革热。D．造成50年代登革热流行。这是由另一种蚊子引起的。E．取代另一种蚊子在亚洲的影响。未提。
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