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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.
The successful attempt to save a badly bitten boy in 1885 was based on the theory that______.
选项 A、infective agent of rabies could be used for vaccination
B、a series of injections of new virus could make people resistant to rabies
C、the infective agent of rabies could be recovered from the infected body
D、the longer incubation period would enable human body to build up enough resistance
答案D
解析 推断判断题。第四段的倒数第二句提到疫苗应用的理论依据是：如果狗在两周内因注射疫苗而受到保护的话，那么人体更长的疾病潜伏期可使人通过疫苗在狂犬病发作之前在体内形成保护机制。只有选项D是对这一理论的概括。
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