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 susceptible to rabies. The people of ancient Egypt, Greece and Rome
ascribed rabies to evil spirits because ordinarily gently and friendly animals
suddenly became vicious and violent without evident cause and, after a period of
maniacal behaviour, became paralysed and died.
Experiments
carried out in Europe in the early nineteenth century of injecting saliva from a
rabid 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 centres
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(腺) and
passes into the saliva so that the bite of the infected animal introduces the
virus 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(潜伏期) 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 paralysed. 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.
Anti-rabies vaccine(疫苗) 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 rabid animals are
given a course of daily injections over a week or ten days. The mortality rate
from all types of bites from rabid 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
circumspectly, and examined professionally or
destroyed. |
