Emerging infections: a perpetual challenge

Emerging and re-emerging infectious diseases, and their determinants, have recently attracted substantial scientifi c and popular attention. HIV/AIDS, severe acute respiratory syndrome, H5N1 avian influenza, and many other emerging diseases have either proved fatal or caused international alarm. Common and interactive co-determinants of disease emergence, including population growth, travel, and environmental disruption, have been increasingly documented and studied. Are emerging infections a new phenomenon related to modern life, or do more basic determinants, transcending time, place, and human progress, govern disease generation? By examining a number of historically notable epidemics, we suggest that emerging diseases, similar in their novelty, impact, and elicitation of control responses, have occurred throughout recorded history. Fundamental determinants, typically acting in concert, seem to underlie their emergence, and infections such as these are likely to continue to remain challenges to human survival. Introduction 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 avia