Viral diseases have the distinction of being among the oldest recorded human diseases (such as rabies and polio) as well as some of the most recently described (such as AIDS). The advancement of virology accelerated during the nineteenth century. First, careful clinical observations led to the identification and differentiation of a number of viral illnesses (such as smallpox from chickenpox and measles from rubella). Second, this improved clinical definition of illnesses combined with improvements in pathologic techniques and methods allowed the pathologic substrate of many viral diseases to be identified. Finally, the work of Pasteur started the systematic use of laboratory animals to study the pathogenesis of disease (10:1124).
With the beginning of the twentieth century, the first viruses were identified. Beijerinck identified tobacco mosaic virus and Loeffler and Frosch discovered foot and mouth disease virus. Then yellow fever, the first human disease-causing virus was discovered, and the seminal work on the pathogenesis of yellow fever by Walter Reed and the Army Yellow Fever Commission was begun.
In the 1940s, using bacteriophages as a model, Delbruck, Luria, and others established many of the basic principles of microbial genetics and molecular biology and identified the major events in the viral growth cycle. The experiments of Avery and associates on the transformation of pneumococcal types, which established that DNA was the genetic material, set the stage for the experiments by Hershey and Chase showing that the genetic material of bacteriophages was also DNA. In the late 1940s, Enders and colleagues grew poliovirus in tissue culture. This work led to the subsequent development of both formalin-inactivated (Salk) and live attenuated (Sabin) vaccines for polio--and the modern era of virology began (10:1124).
Technical advances, such as the development of electron microscopy, ultracentrifugation, and techni...