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  3. Rabies is an ordinarily infectious disease of the central nervous system, caused by a virus and, as a rule, spread chiefly by do

Rabies is an ordinarily infectious disease of the central nervous system, caused by a virus and, as a rule, spread chiefly by do

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问题    Rabies is an ordinarily infectious disease of the central nervous system, caused by a virus and, as a rule, spread chiefly by domestic dogs and wild flesh-eating animals. Man and all warm-blooded animals are easily infected with rabies. The people of ancient Egypt, Greece and Rome ascribed rabies to evil spirits because ordinarily gentle and friendly animals suddenly be came, vicious and violent without evident cause and after a period of maniacal behaviour, be came paralyzed and died.
     Experiments carried out in Europe in the early nineteenth century of injecting saliva from arabid dog into a normal dog proved that the disease was infectious. Preventive steps, such as the destruction of stray dogs, were taken and by 1826 the disease was permanently eliminated in Norway, Sweden and Denmark. Though urban centers on the continent of Europe were cleared several times during the nineteenth century, they soon became  reinfected since rabies was uncontrolled among wild animals.
     During the early stages of the disease, a rabid animal is most dangerous because it appears normal and friendly, but it will bite at the slightest provocation. The virus is present in the salivary glands and passes into the saliva so that the bite of the infected animal introduces the vi ms into a fresh wound. If no action is taken, the virus may become established in the central nervous system and finally attack the brain. The incubation period varies from ten days to eight months or more, and the disease develops more quickly the nearer to the brain the wound is. Most infected dogs become restless, nervous, and irritable and vicious, then depressed and paralyzed. With this type of rabies, the dog’s death is inevitable and usually occurs within three to five days after the onset of the symptoms.
     In 1881 Pasteur discovered that the infective agent of rabies could be recovered from the brain of an animal that had died of rabies. He experimented on rabbits and developed a new variety of rabies which could safely be used for vaccination. A series of injections of this new virus made dogs resistant to the common natural virus. For the first time in 1885 the substance was used in a desperate attempt to save a badly bitten boy. The theory was that if dogs could protected in a two-week period, the longer incubation period of human beings would allow the development of a high degree of protection before the potential onset of the disease. The treatment proved successful and the boy remained well.
     Anti-rabies vaccine is widely used nowadays in two ways. Dogs may be given three-year protection against the disease by one powerful injection, while persons who have been bitten by rabies animals has dropped from 9% to 0.5%. In rare cases, the vaccine will not prevent rabies in human beings because the virus produces the disease before the person’s body has time to build up enough resistance. Because of this, immediate vaccination is essential for anyone bitten by an animal observed acting strangely and the animal should be captured cautiously, and examined professionally or destroyed.
A rabid animal is most dangerous during the early stage of the disease because______.
选项 A、it becomes restless, nervous and violent
B、its bite is fatal
C、the potential danger of the sick animal may be ignored
D、it will attack people at any time
答案C
解析 判断题。第三段的第一句提出疾病早期的动物最危险，因为它们看起来似乎正常友好，但却很容易被激怒而咬人。选项中只有C项的意思与原文最相近。
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