"Infectious diseases are responsible for 15 million (26%) of 57 million annual deaths in a global population of 6.2 billion, a proportion that could rise substantially as chronic diseases continue to be reclassified as infectious--eg, cervical cancer (human papillomavirus), Kaposi's sarcoma (human herpesvirus 8), and Helicobacter pylori ulcers, among others. In recent years, the terms 'emerging' (ie, newly recognized) and 're-emerging' (previously recognized) infectious diseases have entered the vocabulary of medical science. These infections also include 'deliberately emerging diseases'--eg, bioterrorism. Concern about emerging infections has grown following the appearance of new diseases, such as HIV/AIDS, and the re-emergence of others, such as dengue, and from appreciation of the complex determinants of their emergence--eg, microbial adaptation to new hosts (HIV infection, severe acute respiratory syndrome [SARS]), population immunity pressures (influenza A), travel (acute haemorrhagic conjunctivitis), animal migration and movement (West Nile virus infection, H5N1 avian influenza), microbial escape from antibiotic pressures (multidrug-resistant and extensively drug-resistant tuberculosis), mechanical dispersal (Legionnaires' disease), and others (panel, figure 1)."
National Institute of Allergy and Infectious Diseases: http://www3.niaid.nih.gov/
The Lancet Infectious Diseases (November 2008), v.8, p.710-19