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Infectious Diseases � New and Ancient Threats to World Health
Population Bulletin, Vol. 52, No. 2, July 1997
by S. Jay Olshansky, Bruce Carnes, Richard G. Rogers, and Len Smith
Introduction
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 HIV, the virus that causes
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.
Migration within and among countries brings new strains of measles, influenza, and
sexually transmitted diseases to destination areas, and exposes the newcomers to strains
of these diseases that did not exist in their home communities. With cheaper and faster
transportation, international business and pleasure travel can spread infectious and
parasitic diseases around the world in a matter of hours. Modern medical and agricultural
practices-especially the overuse of antibiotics and pesticides � also unwittingly promote
the rise of drug-resistant strains of infectious diseases and pesticide-resistant insects
and other disease carriers. The epidemic of illegal drug use that began in the 1980s also
contributed to the rise and spread of HIV, hepatitis, and other IPDs.
The emergence of new IPDs, and the re-emergence of old ones, have already affected the
growth and age structure of the world's population. The HIV epidemic has produced
some of the most rapid and dramatic demographic effects of IPDs in this century. HIV/AIDS
has slowed population growth in sub-Saharan Africa and has the potential to halve the
average life expectancy at birth in some African countries by 2010.
Outbreaks of cholera or Ebola virus tend to have more concentrated and short-term
demographic effects, but they exact social, psychological, and economic costs that can
disrupt economic development and perpetuate the poverty and squalid living conditions that
foster the spread of infectious diseases.
In this Population Bulletin we use an interdisciplinary approach, interweaving
scientific expertise from the fields of demography, epidemiology, ecology, and evolution
biology to examine the forces responsible for the re-emergence of infectious and parasitic
diseases, explore the various responses available to the medical and scientific community,
and identify some demographic consequences of this new and important development in the
health and living conditions of people throughout the developed and developing world.
The full text of this Population Bulletin is available in print only. Please visit our online store to order. Listed below are all the sections of this Bulletin.
Introduction
Health Burden of Infectious and Parasitic Diseases
Signs of Emergence and Re-Emergence
The Ecology of IPDs
Demographic Change
Social, Economic, Political, and Cultural Factors
Changes to the Natural Environment
Medical Technology and Evolving Risk Factors
Slowing the Rise of IPDs
Conclusion
Discussion
References
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