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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.
The passage suggests that a lack of modern sanitation would make which of the following most likely to occur?
选项 A、An outbreak of Lyme disease.
B、An outbreak of dengue hemorrhagic fever.
C、An epidemic of typhoid.
D、An epidemic of paralytic polio among infants.
E、An epidemic of paralytic polio among adolescents and adults.
答案C
解析 作者指出，缺乏现代卫生手段会使哪件事发生?原文L8—20，现代卫生手段反而促使脊髓灰质炎造成更多瘫痪，并明确指出：能抵御伤寒流行的卫生措施反而会造成瘫痪型脊髓灰质炎流行。取非得：C．正确，伤寒流行。A、B、D、E皆不符合上述推理。
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