病毒学双语版课件Cha(1)

• At the simplest level there is the question, what is disease? An all-embracing definition would be that it is a departure from the normal physiological parameters of an organism.
• Most disease states are multi-factorial at one level or another.
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Chapter 7: Pathogenesis
Virus Diseases
Two components are involved: • the direct effects of virus replication • the effects of bodily responses to the infection
• It is sometimes said that viruses would disappear if they killed their hosts - this is not necessarily true.
• It is possible to imagine viruses with a hit-and-run strategy, moving quickly from one dying host to the next & relying on continuing circulation for their survival.
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Chapter 7: Pathogenesis
Pathogenicity
• Pathogenicity, the capacity of one organism to cause disease in another, is a complex & variable phenomenon.
• In some virus infections, most of the pathologic symptoms observed are attributable not to virus replication, but to the sideeffects of the immune response.
• Nevertheless, there is a clear tendency foቤተ መጻሕፍቲ ባይዱ viruses not to injure their hosts if possible.
Chapter 7: Pathogenesis
Pathogenesis
Learning Objectives: On completing this session, you should be able to:
• Explain the concept of pathogenesis in the context of virus infections.
• Inflammation, fever, headaches & skin rashes are not usually caused by viruses themselves, but by the cells of the immune system due to the release of potent chemicals such as interferons & interleukins.
• In the most extreme cases, none of the pathologic effects of certain diseases are caused directly by the virus, except that its presence stimulates the activation of the immune system.
• This could range from a transient & very minor condition such as a slightly elevated temperature or rather subjective feelings of lethargy to chronic pathologic conditions which eventually result in death.
• Discuss the molecular basis for virus-induced immunodeficiency (including AIDS) & cell transformation by viruses.
• Understand the ways in which virus infection may result in cellular injury.
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Chapter 7: Pathogenesis
Virus Pathogenesis
• Virus pathogenesis is an abnormal & fairly rare situation the majority of virus infections are silent & do not result in outward signs of disease.
• The course of any virus infection is determined by a delicate & dynamic balance between the host & the virus, as is the extent & severity of virus pathogenesis.
• Any of these conditions may result from a large number of internal or external sources.
• However, there is rarely one single factor which 'causes' a disease.