AIDS, SARS, influenza, West Nile fever, cholera, tuberculosis, ebola -- these diseases represent only some of the threats to public health that have exploded over the past decades. Today, we live in one microbial world, since the global spread of any disease could take only the hours required for an airliner to travel from even the most remote area to major population centers.
A classic case of such stunningly rapid spread was the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2002. The epidemic apparently began with a single "super-infector" -- a man in a remote Chinese province. In only months the epidemic expanded and spread to other provinces in China, to Hong Kong, to other Asian countries, and through a single Canadian couple, to Canada. Eventually the disease appeared in dozens of countries, killing hundreds of people before it was contained.
The SARS outbreak also exemplifies the fact that poor public health practices in even the remotest region can have global effects. The SARS virus was likely an animal virus that jumped to humans due to the Chinese fondness for meat from exotic animals and to unsanitary handling practices.
Given the increasing intrusion of humans into formerly inaccessible regions of the globe, even the most isolated reservoirs of disease now have the potential to trigger unchecked worldwide spread. The AIDS virus apparently originated as humans in Africa came into contact with chimpanzees, which harbored the virus as a benign infection.
The economic impact of such diseases is immense. According to the World Health Organization, the cost of influenza alone, for example, is estimated at between $71 billion and $167 billion a year in the U.S., due to hospital and other health care costs and lost productivity.* Such human and economic costs occur even in a "normal" year for influenza, and they will certainly skyrocket in the event of the inevitable worldwide flu pandemic that is predicted by public health experts. The pandemic of 1918-1919, the most devastating epidemic in recorded history, killed as many as 40 million people.
The tracking and treatment of such emerging diseases has been enormously aided by new genomic technologies, vaccines, drugs and international cooperation and communications. Nevertheless, the confluence of poverty, war and poor public health practices in developing countries guarantees that existing diseases remain profound global threats, and the rise of new diseases is inevitable.