Factors contributing to the occurrence of emerging infectious diseases.

Emerging infectious diseases (EIDs) have been receiving increasing attention for more than two decades. Such attention has resulted from observations of increasing resistance of microorganisms to the usual antibiotics, the identification of formerly unknown disease agents and the diseases they cause, and the realization that the concept of globalization includes global exposure to disease agents formerly confined to small, endemic, or remote areas. Sadly, in the fall of 2001, the potential for using microbial agents as instruments of terror and destruction became obvious with the incidents of anthrax spread in the United States, mainly through the mail, although chemical and biological agents had already been used in this way in the past century. The relationship between infectious diseases and social, political, and economic change from the earliest times to the present has been well documented. Emerging infectious diseases and their basic causes present a threat to the stability of nations and indeed the world. Reasons for the emergence/reemergence of infectious diseases are complex and interrelated. The global village provides global economic and social opportunities but also opportunities for disease emergence and transmission. Although characteristics of microorganisms such as genetic adaptive changes are important in the emergence of infectious diseases, factors under human control play a large role. Behavioral and lifestyle choices are also a major influence on the emergence and spread of many EIDs and require attention. Factors contributing to the appearance of emerging and reemerging infectious diseases are discussed.