Chapter 4 : Overview of the Viral Pathogens

Abstract:

There are at least four practical reasons for immunologists to have a good working knowledge of virology. The first is that viruses remain a major cause of human morbidity and mortality and pose a constant potential for causing devastating plagues. Second, viruses are important vectors for vaccines against viral pathogens and nonviral pathogens. Third, viruses are evolution’s gift to gene therapists. Finally, viruses are extremely useful experimental tools and probes for understanding the biology of cells and organisms. The requirement of viral genomes to reach the cytosol provides an early opportunity for recognition by the adaptive immune system in the absence of viral gene expression. Viral penetration of cells has four potential outcomes. First, the cell may be completely inhospitable and the viral proteins and nucleic acids are disposed of with minimal perturbation of the host cells. Second, viral replication initiates but fails to produce infectious progeny, with consequences for the cell ranging from minimal transient perturbations to death. Third, viral replication results in the generation of infectious progeny and cells either are killed immediately or remain persistently infected and continue to function as they produce progeny viruses. Fourth, the virus enters a latent state and essentially disappears until it is triggered to reactivate, with the production of infectious progeny. The chapter focuses on genetic instability of viruses, species specificity, pathogenicity, and vulnerability to immune attack.