When smallpox was eradicated from the globe in the late 1970s, many health experts assumed that infectious and parasitic diseases (IPDs) could at long last be conquered. Death rates from infectious and parasitic diseases had declined during the late 19th century and throughout the 20th century thanks to better public health and sanitation as well as medical advances made possible by economic development. During this period, scientists discovered the germ theory of disease, identified the epidemiology and natural history of many infectious diseases, and created a host of potent antibiotic drugs that helped save millions of lives. Medical researchers learned to identify and cultivate viruses, which led to vaccines for increasing numbers of diseases.
Since the 1970s, genetic engineering has opened the door to new and more powerful weapons to use in the war against IPDs. These scientific advances in the battle against diseases that had long plagued humans, along with public health campaigns and improved living conditions around the world, appeared to set the stage for the eradication of most, if not all, infectious and parasitic diseases in Europe, the United States, and other industrialized countries. And, although many of the most deadly IPDs were still rampant in low-income countries, many scientists and public health officials expected death rates from infectious and parasitic diseases to wane as countries developed economically and as international health campaigns reached greater proportions of the world's population.
Public health workers and the general public were rudely awakened in the early 1980s with the discovery of the human immunodeficiency virus (HIV), the virus that causes acquired immune deficiency syndrome (AIDS). Medical knowledge and public health systems in the world's wealthiest countries were unable to control or cure this new lethal disease. The shock of the HIV epidemic alerted the public and the scientific community to a phenomenon that had been occurring for a quarter of a century. When scientists reviewed the epidemiologic evidence of the previous 25 years, they were able to document the emergence of new forms of old diseases and some apparently "new" diseases that threaten public health in wealthy as well as low-income countries.
More than 28 "new" or previously unrecognized disease-causing microbes have been identified since 1973.Just since 1995, a new strain of cholera (number 0139) has surfaced in Africa and Asia-killing thousands of people. In addition, there have been outbreaks of diphtheria in Laos, Thailand, and the United States; dengue, and the more serious dengue hemorrhagic fever, in India, Malaysia, and Venezuela; various forms of meningitis in parts of Europe, North America, and West Africa; and Ebola in sub-Saharan Africa. At the same time, multidrug-resistant forms of tuberculosis (TB), meningitis, and other bacterial infections have appeared, making these infections much harder to treat.
As health officials and scientists from various disciplines examined the forces responsible for these unexpected developments, they realized that the hope that IPDs would soon be conquered was premature. They linked the rise in infectious and parasitic diseases to a breakdown in public health measures in many countries. They also uncovered ominous signs that new global health and environmental conditions make the world ripe for the re-emergence of IPDs as major causes of death and disability.
Increasing urbanization, for example, brings more people into contact with infectious microbes, especially under the crowded and unsanitary living conditions prevalent in the world's largest cities. Human activity in remote rain forests and sparsely populated savannas exposes people to microbes, such as Ebola, the deadly Hantaan virus, and possibly HIV, that previously existed only in plants and animals. Global climate change, including the depletion of the ozone layer because of increased consumption of fossil fuels, has shifted and expanded the habitats of mosquitoes and other arthropods that transmit IPDs to humans. …