Throughout human history, infectious diseases have caused debilitation and premature death to large portions of the human population, limited human activities, and shaped the course of history. But in the twentieth century modern antibiotics, vaccines, and sanitation methods seemed to have conquered infectious disease, and in the late 1960's, U.S. Surgeon General William H. Stewart state that we could "close the book on infectious disease."1 Even as late as 1988, infectious disease didn't even make the Top Ten List of causes of death in the United States.
But by the 1990's the supposedly defeated foe reemerged with a vengeance, including killer infectious diseases such as AIDS, Lyme disease, Legionnaire's disease, Ebola, Hantavirus, West Nile virus, tuberculosis, BSE, and SARS. These "emerging diseases" are either new pathogens that have appeared and quickly spread through populations or already known pathogens that have become resurgent, once again threatening wider and wider populations.
Infectious diseases are now the world's number one killer. In the US, deaths from infections in jumped 22% from 1980-1992, and as of 1995 infectious diseases were the third leading cause of death and still climbing.2 One-third of the world's population has tuberculosis, and 1 in 10 tuberculosis cases is resistant to antibiotics3. The HIV/AIDS pandemic is devastating many countries, with Sub-Saharan Africa being hardest hit. In Botswana and Swaziland, HIV/AIDS has reduced life expectancy by more than 20 years4, and HIV prevalence is at 39%5.
Biology 189L - Emerging Infectious Diseases will focus on the biology of emerging diseases, the causes of their emergence or reemergence of infectious diseases, and strategies for coping with them. As stated by Joshua Lederberg, the Nobel prize winner who coined the term "emerging disease" and who co-chaired the Institute of Medicine Committee on Emerging Microbial Threats, "If we were to rely strictly on biologic selection to respond to the selective factors of infectious disease, the population would fluctuate from billions down to perhaps millions before slowly rising again. Therefore, our evolutionary capability may be dismissed as almost totally inconsequential. In the race against microbial genes, our best weapon is our wits, not natural selection on our genes."6
What is an "emerging infectious disease"?
Here are some definitions from the Emerging Infectious Diseases journal (Centers for Disease Control and Prevention), the Institute of Medicine (National Academy of Sciences), and the National Institute of Allergy and Infectious Diseases (National Institutes of Health):
"Emerging" infectious diseases can be defined as infections that have newly appeared in a population or have existed but are rapidly increasing in incidence or geographic range.7
Emerging infections are those whose incidence in humans has increased within the past two decades or threatens to increase in the near future. Emergence may be due to the spread of a new agent, to the recognition of an infection that has been present in the population but has gone undetected, or to the realization that an established disease has an infectious origin. Emergence may also be used to describe the reappearance (or "reemergence") of a known infection after a decline in incidence.8
Emerging infectious diseases are diseases that (1) have not occurred in humans before (this type of emergence is difficult to establish and is probably rare); (2) have occurred previously but affected only small numbers of people in isolated places (AIDS and Ebola hemorrhagic fever are examples); or (3) have occurred throughout human history but have only recently been recognized as distinct diseases due to an infectious agent (Lyme disease and gastric ulcers are examples).9
References:
Stewart, William H. 1967. "A Mandate for State Action," presented at the Association of State and Territorial Health Officers, Washington, DC, Dec. 4, 1967. (This quote is often cited as a report or testimony to Congress in 1969, but I have been unable to find such testimony in the Congressional record.)
Pinner, R. W. et al. 1996. Trends in infectious disease mortality in the United States. JAMA - Journal of the American Medical Association 275: 189-193.
World Health Organization. "Tuberculosis," Fact Sheet No 104. Revised August 2002. [html]
World Health Organization. "The world health report 2003 - shaping the future." [html | pdf]
Lederberg, J. 1997. Infectious Disease as an Evolutionary Paradigm. Emerging Infectious Diseases 3: 417-423. [html | pdf]
Stephen S. Morse. 1995. "Factors in the Emergence of Infectious Diseases." Emerg. Infect. Dis. Vol.1 No.1. [html | pdf]
Institute of Medicine. "Emerging Infections: Microbial Threats to Health in the United States." National Academy Press, Washington, D.C. 1992. [html]
National Institute of Allergy and Infectious Diseases. "Understanding Emerging and Re-emerging Infectious Diseases." October 1999. [pdf]
Sources for images:
Collage of hantavirus headlines from "All About Hantavirus", and Prevention (http://www.cdc.gov/ncidod/diseases/hanta/hps/noframes/outbreak.htm)
False color electron micrograph of Ebola virus from the World Health Organization (http://www.who.int/emc/diseases/ebola/ebolapic.html)
Lyme disease risk map from "Lyme Disease Fact Sheet", Centers for Disease Control and Prevention (http://www.cdc.gov/od/oc/media/fact/images/riskmap_ld.gif)
