ABSTRACT
Infectious diseases have assumed an important role in the evolution of the human race and the history of mankind. Survival of man during the prehistoric era depended on avoiding predators. Subsequently, the ushering in of civilization brought new threats for survival. Infectious diseases became the major cause of death and disability until the mid-20th century. Outbreaks such as smallpox, plague, cholera, typhoid fever, diphtheria, tuberculosis, and typhus fever have been responsible for the deaths of millions of people (1). As recently as 1918, an international epidemic of "Spanish flu" (strain of influenza virus) accounted for 21 million deaths in all parts of the world, including approximately 550,000 deaths in the United States (2). In addition, certain infections resulted in death and often caused severe disabilities, deformities, and functional incapacities, such as mumps, measles, scarlet fever, rheumatic fever, pertussis, poliomyelitis, and syphilis (1). Not surprisingly, childhood mortality was very high. It is for this reason that, up until the mid-1900s, life expectancy was relatively limited (approximately 47 years in the United States) (3).
