Abstract
Infectious diseases are one of the leading causes of human deaths worldwide. They have devastated human life for a very long time; however, with advancements in diagnostics, prevention, and therapeutic approaches, they were controlled to a manageable extent during the second half of the 20th century. It was assumed that humankind has successfully defeated the threat of infectious diseases. However, many infectious diseases have undergone re-emergence and are now a major cause of concern. Besides, there is the emergence of several new infectious diseases. These diseases are termed re-emerging and emerging infectious diseases, and collectively account for more than 20 infectious diseases. World Health Organization has identified these diseases as the predominant health hazard faced by human beings. Owing to this situation, there is an urgent need to revisit infectious diseases and make efforts towards the development of anti-microbial drugs for emerging and reemerging microbial diseases. The present book chapter aims to provide a comprehensive account of re-emerging and newly emerging infectious diseases and the paradigm shift of antimicrobial drugs in the 21st century. It is expected to provide useful insight into this important research and development area.