ques for the electrophoresis of nucleic acids and proteins, set the stage for improved understanding of viral structure and for a detailed biochemical analysis of purified virion components and their biologic properties. The use of x-ray crystallography has allowed structural definition of viruses and their components at a near-atomic level. By using the techniques of molecular biology, the entire genomes of many viruses have been sequenced. Monoclonal antibodies have enabled specific domains on viral proteins to be defined with great precision. For example, the polymerase chain reaction (PCR) technique allows small amounts of nucleic acid. Techniques such as this may prove to be greatly superior to conventional serologic approaches to diagnosis of viral diseases. Among the challenges for the future will be the application of new techniques to understand at the molecular level of how viruses interact with target cells to alter function, how the interaction of viruses and cells within a living host produce disease, and how events in the infected host result in the transmission disease and the maintenance of infectious viruses in the environment. Improved understanding of these aspects of viral infection should lead to new approaches to the diagnosis, prevention, and cure of viral diseases (10:1124).
The first classification of viruses as a group distinct from other microorganisms was based almost exclusively on their ability to pass through filters of a small pore size. Initial subdivisions were based primarily on pathologic properties such as specific organ tropism (enteroviruses) or on common epidemiologic features such as transmission by arthropod vectors (arboviruses). Since the 1950s, classification has depended predominantly on morphologic and physicochemical criteria. More recently, the availability of an increasing body of knowledge concerning the nucleic acid properties of many viral genomes has led to attempt to re...