# Test 2, Lecture 11 Definition of viral disease Symptoms of ill health as a result of viral infection Infection presence and/or growth of a virus in an organism; not all infections result in disease (most do not). Pathogenicity capacity to cause disease True/False: Most viruses are pathogenic True True/False: All infections result in disease False; not all infections result in disease (most do not) Virulence Efficiency with which a virus causes disease Disease is likely to result from a... infection by a virulent pathogenic virus How to viruses cause disease? Cytopathic effect Cytopathic effect At the cellular level, disease is the result of the cytopathic effect (and cell damage leads to tissue damage). Morphological, structural, and molecular changes in the cell that disrupt function Cell death Called cytocidal effect; sometimes from immune response, sometimes from apoptosis Steps of cytopathic effect Viral infection --> interrupt cell function --> cell damage (promotes release of lysosomes) --> cell death Patterns of infection acute (most recognizable); inapparent; persistent; transforming Most recognizable pattern of infection acute Stages of acute infection incubation (extremely variable in time period; asymptomatic, detectable only by molecular tests); prodromal (general symptoms, can't identify cause); disease (specific symptoms, can identify virus by symptoms); death or recovery (asymptomatic). Most important result of Fenner experiment By the time disease is detected, the virus has infected all tissues that can be infected. Examples of acute infections cold, flu Inapparent infections viral infections without disease; low virulence, defense system wins; important as carriers of pathogenic viruses Persistent infections Isolate virus over long period of time; symtoms occur or reoccur long after initial infection. Types of persistent infections latent (intermittent acute episodes of disease: herpes simplex); chronic (constant viral multiplication; may or may not show disease); slow (long incubation period followed by slow progressive disease). Transforming infections Some viruses transform cells, causing malignant tumors.