Читать книгу Basic Virology - Martinez J. Hewlett - Страница 76

Once the symptoms of disease become apparent, rabies virus infections are almost always fatal. The virus targets salivary tissue in the head and neck in order to provide itself with an efficient medium for transmission to other animals. Involvement of the CNS and brain is eventually widespread, with ensuing neuronal dysfunction. Prior to this, however, the involvement is only with specific cells that lead to alterations in the afflicted animal's behavior and ability to deal with sensory stimuli. During this period, which is often preceded by a prodromal period of altered behavioral patterns, the animal can be induced to an aggressive biting frenzy by loud sounds or by the appearance of other animals. This course is the “furious form” of the disease. This behavioral change is most marked for carnivores such as dogs, cats, and raccoons, but can be observed in other infected animals such as squirrels and porcupines. The behavioral changes obviously have a marked impact on transmission of the virus, as the frenzied animal bite is often the instrument of spread.

Despite its association with frenzy (the name rabies is derived from the Sanskrit term for doing violence), not all rabies infections lead to the furious form. There is another form of the disease (often termed “dumb”) in which the afflicted animal becomes progressively more torpid and withdrawn, eventually lapsing into a coma and death.

The disease's long incubation period between the time of initial inoculation and final death is a very important factor, both in spread of the virus and in its being able to persist in wild populations, but there is also evidence that some animals can be carriers of the disease for long periods with no obvious, overt symptoms. While there are (extremely) rare examples of apparent recovery from the disease even after symptoms appear, generally one can consider the development of the symptoms of rabies as tantamount to a death sentence.