Читать книгу Basic Virology - Martinez J. Hewlett - Страница 74

While all the organ systems of the vertebrate host have important or vital functions in the organism's life, several play such critical roles that their disruption leads to serious consequences or death. Among these are the CNS with its influence on all aspects of behavior both innate and learned, the circulatory system, the immune system, and the liver. Virus infections of these systems are often life‐threatening to the infected individual, and the tissue damage resulting from infection can lead to permanent illness or death. For example, destruction of CD4+ T cells of the immune system by HIV is the major symptom of AIDS and leads in >90% of untreated cases to death from opportunistic infections and neoplasms. Other viruses can cause as devastating a disease as HIV, but most viral infections are not as often fatal. A consideration of some CNS and liver virus infections provides some interesting examples of both destructive and limited disease courses.

The different patterns of sequelae following infection of a common target organ are also important demonstrations of several features of virus infection and pathogenesis.

First, specific tissue or cell tropism is a result of highly specific interactions between a given virus and the cell type it infects. Depending on the type of cell infected, the severity of symptoms, and the nature of the damage caused by the infection, different outcomes of infection are evident.

Second, persistent infection is a complex process. It is, in part, the result of virus interacting with and modulating the host's immune system. Often, persistence involves the virus adapting to a continuing association with the target cell itself.

Third, classifying viruses by the diseases they cause is not a particularly useful exercise when trying to understand relationships among viruses.

Fourth, and finally, viruses spread by very different routes can target the same organ. The movement of virus within the host is as important as the initial port of entry for the virus.