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Despite decades of dramatic progress in their treatment and prevention, infectious diseases remain a major cause of death and debility and are responsible for worsening the living conditions of many millions of people around the world. Infections frequently challenge the physician's diagnostic skill and must be considered in the differential diagnoses of syndromes affecting every organ system. | Chapter 113. Introduction to Infectious Diseases Host-Pathogen Interactions Despite decades of dramatic progress in their treatment and prevention infectious diseases remain a major cause of death and debility and are responsible for worsening the living conditions of many millions of people around the world. Infections frequently challenge the physician s diagnostic skill and must be considered in the differential diagnoses of syndromes affecting every organ system. Changing Epidemiology of Infectious Diseases With the advent of antimicrobial agents some medical leaders believed that infectious diseases would soon be eliminated and become of historic interest only. Indeed the hundreds of chemotherapeutic agents developed since World War II most of which are potent and safe include drugs effective not only against bacteria but also against viruses fungi and parasites. Nevertheless we now realize that as we developed antimicrobial agents microbes developed the ability to elude our best weapons and to counterattack with new survival strategies. Antibiotic resistance occurs at an alarming rate among all classes of mammalian pathogens. Pneumococci resistant to penicillin and enterococci resistant to vancomycin have become commonplace. Even Staphylococcus aureus strains resistant to vancomycin have appeared. Such pathogens present real clinical problems in managing infections that were easily treatable just a few years ago. Diseases once thought to have been nearly eradicated from the developed world tuberculosis cholera and rheumatic fever for example have rebounded with renewed ferocity. Newly discovered and emerging infectious agents appear to have been brought into contact with humans by changes in the environment and by movements of human and animal populations. An example of the propensity for pathogens to escape from their usual niche is the alarming 1999 outbreak in New York of encephalitis due to West Nile virus which had never previously been isolated in the .
