ABSTRACT
This chapter introduces the basic viral structures and modes of replication and presents the consequences of these properties for the different virus families. Human viruses range in size and complexity from the tiny Norwalk virus, which causes outbreaks of diarrhea, to the poxviruses, which are almost visible under a light microscope. Every virus must replicate and produce more viral progeny or disappear. The mechanism of virus entry into the cell depends on the virion structure. Most RNA viruses replicate in the cytoplasm, which provides easy access to the ribosome for protein synthesis. Most capsid viruses accumulate in the cytoplasm and must cause the cell to lyse in order to be released. Most viral diseases are caused by a combination of viral pathogenesis and immunopathogenesis. Viral pathogenesis is caused by changes in the cell that are induced by viral replication and viral replication-induced cell death.
