Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 17 Introduction Humanity shares a common ancestry with all living things on Earth. We often share especially close intimacies with the microbial world. In fact, only a small percentage of the cells in the human body are human at all. ‘‘We’’ are vastly outnumbered, even within our bodies, by microbial life that can only be counted on the same scale as the vast numbers of stars in the universe. This is also an essential relationship, because humanity could not survive without an array of microflora that both nourish us and that provide needed enzymes for life processes. Yet, the common biology and biochemistry that unites us also makes us susceptible to contracting and transmitting infectious disease. Throughout history, microorganisms have spread deadly diseases and caused widespread epidemics that have threatened and altered human civilization. In the modern era, civic sanitation, water purification, immunization, and antibiotics have dramatically reduced the overall morbidity and the mortality rates of infectious disease in more developed nations. Yet, much of the world is still ravaged by disease and epidemics; new threats constantly appear to challenge the most advanced medical and public health systems. Although specific diseases may be statistically associated with particular regions or other demographics, disease does not recognize social class or political boundary. In our intimately connected global village, an outbreak of disease in a remote area may quickly transform into a global threat. Given the opportunity, the agents of disease may spread across the globe at the speed of modern travel, and also leap from animals to humans. The articles presented in these volumes, written by some of the world’s leading experts, are designed to be readable and to instruct, challenge, and excite a range of student and reader interests while, at the same time, providing a solid foundation and reference for more advanced students and readers. It speaks both to the seriousness of their dedication to combating infectious disease and to the authors’ great credit that the interests of younger students and lay readers were put forefront in preparation of these entries. The editors are especially pleased to have contributions and original primary source essays within the volumes by experts that are currently in the forefront of international infectious disease research and policy. Jack Woodall, Ph.D., recounts memories of belonging to a team that identified and determined the cause of Machupo hemorrhagic fever in ‘‘Virus Hunters’’ and of his association with the developer of the yellow fever vaccine in ‘‘Yellow Fever.’’ He also explains ‘‘ProMED,’’ a disease-reporting system (of which Woodall is a founder) that allows scientists around the world, whether in the hospital, laboratory, or the field, to share real-time information about outbreaks of emerging infectious diseases. Jack Woodall now serves as the director of the Nucleus for the Investigation of Emerging Infectious Diseases at the Federal University of Rio de Janeiro in Brazil. xvii Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 18 Introduction Stephen A. Berger, M.D., Ph.D., Director of Geographic Medicine at Tel Aviv Medical Center in Tel Aviv, Israel, served as a contributing advisor for Infectious Diseases: In Context and was the developer of GIDEON (Global Infectious Disease and Epidemiology Network), the world’s premier global infectious diseases database. Dr. Berger explains the Web-based tool that helps physicians worldwide diagnose infectious diseases. Dr. Berger also contributes ‘‘Travel and Infectious Disease’’ and a special introduction. Dr. Berger’s contributions reflect a dedication to teaching that has five times earned him the New York Medical College Teaching Award. Dr. Berger, author of numerous articles and books, including Introduction to Infectious Diseases, The Healthy Tourist, and Exotic Viral Diseases: A Global Guide, was gracious with his time, writing, and advice. The editors are indebted to both of these distinguished scientists for their generous contributions of time and compelling material. Readers interests were are also well-served by Anthony S. Fauci, M.D., Director of the National Institutes of Allergy and Infectious Diseases, for what was, at the time Infectious Diseases: In Context went to press, a preview of his latest version of the map of emerging and re-emerging infectious diseases, and also by L. Scott Clements, M.D., Ph.D., for his advice and articles, including ‘‘Childhood Infectious Diseases: Immunization Impacts.’’ Space limitations of this volume force the editors to include only those infectious diseases that directly affect human health. It is important to note, however, that diseases affecting plants and animals can have a significant indirect impact on the lives of humans. The 2001 outbreak of foot and mouth disease in the United Kingdom, for example, resulted in the slaughter of over six million pigs, sheep, and cattle, crippling farmers, tourism, and other commerce, and ultimately costing an estimated four billion dollars to the U.K. economy. At press time, the cocoa industry in Ghana is threatened by the Cocoa Swollen Shoot Virus, where farmers are reluctant to cut down their infected mature cocoa trees and plant healthy seedlings. Ghana is among the leading exporters worldwide of cocoa for chocolate. Scientists are also concerned about a lack of forthcoming information from the Chinese government concerning an epidemic virus among pigs in China that is contributing to a pork shortage and the strongest inflation in China in a decade. Although these diseases cannot inflict illness in humans, they can ultimately affect the nutritional, social, economic, and political status of a nation and its people. Despite the profound and fundamental advances in science and medicine during the last fifty years, there has never been a greater need for a book that explains the wideranging impacts of infectious disease. It is hubris to assume that science alone will conquer infectious diseases. Globally, deaths due to malaria alone may double over the next twenty years and ominous social and political implications cannot be ignored when death continues to cast a longer shadow over the poorest nations. The fight against infectious disease depends on far more than advances in science and public health. The hope that threats and devastation of infectious diseases could be eliminated for all humankind have long since been dashed upon the hard realities that health care is disproportionately available, and cavernous gaps still exist between health care in wealthier nations as opposed to poorer nations. Victory in the ‘‘war’’ against infectious disease will require advances in science and advances in our understanding of our fragile environment and common humanity. K. Lee Lerner & Brenda Wilmoth Lerner, editors DUBLIN, IRELAND, JULY 2007 Brenda Wilmoth Lerner and K. Lee Lerner were members of the International Society for Infectious Disease and delegates to the 12th International Congress on Infectious Disease in Lisbon, Portugal, in June 2006. Primarily based in London and Paris, the Lerner & Lerner portfolio includes more than two dozen books and films that focus on science and science-related issues. ‘‘. . .any man’s death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bells tolls; it tolls for thee.’’ —John Donne, 1624 (published) Devotions upon Emergent Occasions, no. 17 (Meditation) The book is respectfully dedicated to Dr. Carlo Urbani and those who risk—and far too often sacrifice—their lives in an attempt to lessen the toll of infectious diseases. xviii INFECTIOUS DISEASES: IN CONTEXT Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 19 A Special Introduction by Stephen A. Berger, M.D. The Burden of Infectious Disease in Our Changing, Globalizing World As we move into the twenty-first century, we continue to exist in a sea of ancient, hostile adversaries that threaten our very existence—both as individuals, and as a race of mediumsized mammals. The good news is that modern technology allows us to understand, diagnose, and treat an expanding number of infectious diseases. The bad news is that this same modern technology increasingly places us at risk for those same diseases. For the purpose of clarity, I will classify the infectious diseases of humans into six broad categories: traditional, new, emerging, re-emerging, disappearing, and extinct. The latter category is depressingly small, and in fact contains only a single disease. The last case of smallpox was reported in Somalia in 1977, and the viral agent hibernates (as far as we know) in secure freezers located in the United States and Russian Federation. The few disappearing diseases include measles, leprosy, guinea worm, and poliomyelitis— conditions whose numbers have decreased in recent years, but which could suddenly blossom into outbreaks when the political and social climate permits. One must distinguish between ‘‘new diseases’’ and ‘‘newly discovered’’ diseases. The former category includes conditions that had never before affected mankind: AIDS, SARS, Ebola. In contrast, Legionnaire’s disease, Chlamydial infection, and Lyme disease appear to have affected man for many centuries, but were only ‘‘discovered’’ when appropriate technology permitted. Emerging diseases such as West Nile fever and Dengue are certainly not new, but expand both geographically and numerically with the advent of mass tourism and the dispersal of mosquitoes in suitable animals or other vehicles. As the term implies, ‘‘reemerging’’ diseases such as malaria repopulate areas from which they had been eliminated, often as the result of man-made alteration of the environment, elimination of natural predators, global warming, deforestation, and crowding. The best-known disease in this category is influenza, which is caused by a virus that seems to evolve and mutate continually into agents that are not recognized by the human host. Even this phenomenon is largely driven by the practice of some human populations to raise swine and ducks in crowded, unsanitary conditions that promote interchange of viral material. The vast majority of infectious diseases might be classified as ‘‘traditional,’’ forever with us and largely unchanged: the common cold, chickenpox, urinary tract infection, pneumonia, typhoid, gonorrhea, meningitis, and hundreds of others. In some cases, vaccines have altered the incidence of some traditional diseases among select populations. In other cases, increasing life span and advances in medical and surgical intervention have actually created a favorable ecological niche for heretofore non-pathogenic microbes. xix Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 20 A Special Introduction by Stephen A. Berger, M.D. Sadly, several new and distressing disease patterns have been the direct result of advances in managing the infection itself. Tuberculosis has been a largely treatable disease since the 1940’s; but as of 2007, strains of the causative agent are increasingly resistant to all known drugs. Highly resistant microbes are now commonplace in cases of AIDS, malaria, and gonorrhea, as well as many of the traditional bacteria for which antibiotics were primarily developed: staphylococci, pneumococci and E. coli. Hopefully, the seemingly self-destructive aspect of mankind will be overtaken by continued advances in the treatment, prevention, and understanding of the microbes that share our world. Stephen A. Berger, M.D. Director of Geographic Medicine Tel Aviv Medical Center Tel Aviv, Israel xx INFECTIOUS DISEASES: IN CONTEXT Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 21 About the In Context Series Written by a global array of experts yet aimed primarily at high school students and an interested general readership, the In Context series serves as an authoritative reference guide to essential concepts of science, the impacts of recent changes in scientific consensus, and the effects of science on social, political, and legal issues. Cross-curricular in nature, In Context books align with, and support, national science standards and high school science curriculums across subjects in science and the humanities, and facilitate science understanding important to higher achievement in the No Child Left Behind (NCLB) science testing. Inclusion of original essays written by leading experts and primary source documents serve the requirements of an increasing number of high school and international baccalaureate programs, and are designed to provide additional insights on leading social issues, as well as spur critical thinking about the profound cultural connections of science. In Context books also give special coverage to the impact of science on daily life, commerce, travel, and the future of industrialized and impoverished nations. Each book in the series features entries with extensively developed words-to-know sections designed to facilitate understanding and increase both reading retention and the ability of students to understand reading in context without being overwhelmed by scientific terminology. Entries are further designed to include standardized subheads that are specifically designed to present information related to the main focus of the book. Entries also include a listing of further resources (books, periodicals, Web sites, audio and visual media) and references to related entries. In addition to maps, charts, tables and graphs, each In Context title has approximately 300 topic-related images that visually enrich the content. Each In Context title will also contain topic-specific timelines (a chronology of major events), a topic-specific glossary, a bibliography, and an index especially prepared to coordinate with the volume topic. xxi Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 23 About This Book The goal of Infectious Diseases: In Context is to help high-school and early college-age students understand the essential facts and deeper cultural connections of topics and issues related to the scientific study of infectious disease. The relationship of science to complex ethical and social considerations is evident, for example, when considering the general rise of infectious diseases that sometimes occurs as an unintended side effect of the otherwise beneficial use of medications. Nearly half the world’s population is infected with the bacterium causing tuberculosis (TB); although for most people the infection is inactive, yet the organism causing some new cases of TB is evolving toward a greater resistance to the antibiotics that were once effective in treating TB. Such statistics also take on added social dimension when considering that TB disproportionately impacts certain social groups (the elderly, minority groups, and people infected with HIV). In an attempt to enrich the reader’s understanding of the mutually impacting relationship between science and culture, as space allows we have included primary sources that enhance the content of In Context entries. In keeping with the philosophy that much of the benefit from using primary sources derives from the reader’s own process of inquiry, the contextual material introducing each primary source provides an unobtrusive introduction and springboard to critical thought. General Structure Infectious Diseases: In Context is a collection of 250 entries that provide insight into increasingly important and urgent topics associated with the study of infectious disease. The articles in the book are meant to be understandable by anyone with a curiosity about topics related to infectious disease, and the first edition of Infectious Diseases: In Context has been designed with ready reference in mind: • Entries are arranged alphabetically, rather than by chronology or scientific subfield. • The chronology (timeline) includes many of the most significant events in the history of infectious disease and advances of science. Where appropriate, related scientific advances are included to offer additional context. • An extensive glossary section provides readers with a ready reference for contentrelated terminology. In addition to defining terms within entries, specific Words-toKnow sidebars are placed within each entry. • A bibliography section (citations of books, periodicals, websites, and audio and visual material) offers additional resources to those resources cited within each entry. • A comprehensive general index guides the reader to topics and persons mentioned in the book. xxiii Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 24 About This Book Entry Structure In Context entries are designed so that readers may navigate entries with ease. Toward that goal, entries are divided into easy-to-access sections: • Introduction: A opening section designed to clearly identify the topic. • Words-to-know sidebar: Essential terms that enhance readability and critical understanding of entry content. • Established but flexible rubrics customize content presentation and identify each section, enabling the reader to navigate entries with ease. Inside Infectious Diseases: In Context entries readers will find two key schemes of organization. Most entries contain internal discussions of Disease History, Characteristics, and Transmission, followed by Scope and Distribution, then a summary of Treatment and Prevention. General social or science topics may have a simpler structure discussing, for example, History and Scientific Foundations. Regardless, the goal of In Context entries is a consistent, content-appropriate, and easy-to-follow presentation. • Impacts and Issues: Key scientific, political, or social considerations related to the entry topic. • Bibliography: Citations of books, periodicals, web sites, and audio and visual material used in preparation of the entry or that provide a stepping stone to further study. • ‘‘See also’’ references clearly identify other content-related entries. Infectious Diseases: In Context special style notes Please note the following with regard to topics and entries included in Infectious Diseases: In Context: • Primary source selection and the composition of sidebars are not attributed to authors of signed entries to which the sidebars may be associated. In all cases, the sources for sidebars containing external content (e.g., a CDC policy position or medical recommendation) are clearly indicated. • The Centers for Disease Control and Prevention (CDC) includes parasitic diseases with infectious diseases, and the editors have adopted this scheme. • Equations are, of course, often the most accurate and preferred language of science, and are essential to epidemiologists and medical statisticians. To better serve the intended audience of Infectious Diseases: In Context, however, the editors attempted to minimize the inclusion of equations in favor of describing the elegance of thought or essential results such equations yield. • A detailed understanding of biology and chemistry is neither assumed nor required for Infectious Diseases: In Context. Accordingly, students and other readers should not be intimidated or deterred by the sometimes complex names of chemical molecules or biological classification. Where necessary, sufficient information regarding chemical structure or species classification is provided. If desired, more information can easily be obtained from any basic chemistry or biology reference. Bibliography citation formats (How to cite articles and sources) In Context titles adopt the following citation format: Books Magill, Gerard, ed. Genetics and Ethics: An Interdisciplinary Study. New York: Fordham University Press, 2003. Verlinsky, Yury, and Anver Kuliev. Practical Preimplantation Genetic Diagnosis. New York: Springer, 2005. xxiv INFECTIOUS DISEASES: IN CONTEXT Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 25 About This Book Web Sites ADEAR. Alzheimer’s Disease Education and Referral Center. National Institute on Aging. <http://www.alzheimers.org/generalinfo.htm> (accessed January 23, 2006). Genetics and Public Policy Center. <http://dnapolicy.org/index.jhtml.html> (accessed January 23, 2006). Human Genetics in the Public Interest. The Center for Genetics and Society. <http:// www.genetics-and-society.org> (accessed January 26, 2006). PGD: Preimplantation Genetic Diagnosis. ‘‘Discussion by the Genetics and Public Policy Center.’’ <http://dnapolicy.org/downloads/pdfs/policy_pgd.pdf> (accessed January 23, 2006). Alternative citation formats There are, however, alternative citation formats that may be useful to readers and examples of how to cite articles in often used alternative formats are shown below. APA Style Books: Kübler-Ross, Elizabeth. (1969) On Death and Dying. New York: Macmillan. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. (2006) Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale. Periodicals: Venter, J. Craig, et al. (2001, February 16). ‘‘The Sequence of the Human Genome.’’ Science, vol. 291, no. 5507, pp. 1304–51. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. (2006) Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale. Web Sites: Johns Hopkins Hospital and Health System. ‘‘Patient Rights and Responsibilities.’’ Retrieved January 14, 2006 from Http://www.hopkinsmedicine. org/patients/JHH/patient_rights.html. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. (2006) Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale. Chicago Style Books: Kübler-Ross, Elizabeth. On Death and Dying. New York: Macmillan, 1969. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, MI: Thomson Gale, 2006. Periodicals: Venter, J. Craig, et al. ‘‘The Sequence of the Human Genome.’’ Science (2001): 291, 5507, 1304–1351. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, MI: Thomson Gale, 2006. Web Sites: Johns Hopkins Hospital and Health System. ‘‘Patient Rights and Responsibilities.’’ <http://www.hopkinsmedicine.org/patients/JHH/patient_ rights.html.> (accessed January 14, 2006). Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, MI: Thomson Gale, 2006. MLA Style Books: Kübler-Ross, Elizabeth. On Death and Dying, New York: Macmillan, 1969. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale, 2006. Periodicals: Venter, J. Craig, et al. ‘‘The Sequence of the Human Genome.’’ Science, 291 (16 February 2001): 5507, 1304–51. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Terrorism: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale, 2006. INFECTIOUS DISEASES: IN CONTEXT xxv Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 26 About This Book Web Sites: ‘‘Patient’s Rights and Responsibilities.’’ Johns Hopkins Hospital and Health System. 14 January 2006. <http://www.hopkinsmedicine.org/patients/JHH/ patient_rights.html.> Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Terrorism: Essential Primary Sources, Farmington Hills, Mich.: Thomson Gale, 2006. Turabian Style (Natural and Social Sciences) Books: Kübler-Ross, Elizabeth. On Death and Dying, (New York: Macmillan, 1969). Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, (Farmington Hills, Mich.: Thomson Gale, 2006). Periodicals: Venter, J. Craig, et al. ‘‘The Sequence of the Human Genome.’’ Science, 291 (16 February 2001): 5507, 1304–1351. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, (Farmington Hills, Mich.: Thomson Gale, 2006). Web Sites: Johns Hopkins Hospital and Health System.‘‘Patient’s Rights and Responsibilities.’’ available from http://www.hopkinsmedicine.org/patients/JHH/ patient_rights.html; accessed14 January 2006. Excerpted in K. Lee Lerner and Brenda Wilmoth Lerner, eds. Medicine, Health, and Bioethics: Essential Primary Sources, (Farmington Hills, Mich.: Thomson Gale, 2006). xxvi INFECTIOUS DISEASES: IN CONTEXT Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 27 Using Primary Sources The definition of what constitutes a primary source is often the subject of scholarly debate and interpretation. Although primary sources come from a wide spectrum of resources, they are united by the fact that they individually provide insight into the historical milieu (context and environment) during which they were produced. Primary sources include materials such as newspaper articles, press dispatches, autobiographies, essays, letters, diaries, speeches, song lyrics, posters, works of art—and in the twenty-first century, web logs—that offer direct, first-hand insight or witness to events of their day. Categories of primary sources include: • Documents containing firsthand accounts of historic events by witnesses and participants. This category includes diary or journal entries, letters, email, newspaper articles, interviews, memoirs, and testimony in legal proceedings. • Documents or works representing the official views of both government leaders and leaders of other organizations. These include primary sources such as policy statements, speeches, interviews, press releases, government reports, and legislation. • Works of art, including (but certainly not limited to) photographs, poems, and songs, including advertisements and reviews of those works that help establish an understanding of the cultural milieu (the cultural environment with regard to attitudes and perceptions of events). • Secondary sources. In some cases, secondary sources or tertiary sources may be treated as primary sources. For example, if an entry written many years after an event, or to summarize an event, includes quotes, recollections, or retrospectives (accounts of the past) written by participants in the earlier event, the source can be considered a primary source. Analysis of primary sources The primary material collected in this volume is not intended to provide a comprehensive or balanced overview of a topic or event. Rather, the primary sources are intended to generate interest and lay a foundation for further inquiry and study. In order to properly analyze a primary source, readers should remain skeptical and develop probing questions about the source. Using historical documents requires that readers analyze them carefully and extract specific information. However, readers must also read ‘‘beyond the text’’ to garner larger clues about the social impact of the primary source. In addition to providing information about their topics, primary sources may also supply a wealth of insight into their creator’s viewpoint. For example, when reading a xxvii Infectious Diseases: In Context – Finals/ 9/25/2007 11:15 Page 28 Using Primary Sources news article about an outbreak of disease, consider whether the reporter’s words also indicate something about his or her origin, bias (an irrational disposition in favor of someone or something), prejudices (an irrational disposition against someone or something), or intended audience. Students should remember that primary sources often contain information later proven to be false, or contain viewpoints and terms unacceptable to future generations. It is important to view the primary source within the historical and social context existing at its creation. If for example, a newspaper article is written within hours or days of an event, later developments may reveal some assertions in the original article as false or misleading. Test new conclusions and ideas Whatever opinion or working hypothesis the reader forms, it is critical that they then test that hypothesis against other facts and sources related to the incident. For example, it might be wrong to conclude that factual mistakes are deliberate unless evidence can be produced of a pattern and practice of such mistakes with an intent to promote a false idea. The difference between sound reasoning and preposterous conspiracy theories (or the birth of urban legends) lies in the willingness to test new ideas against other sources, rather than rest on one piece of evidence such as a single primary source that may contain errors. Sound reasoning requires that arguments and assertions guard against argument fallacies that utilize the following: • false dilemmas (only two choices are given when in fact there are three or more options); • arguments from ignorance (argumentum ad ignorantiam; because something is not known to be true, it is assumed to be false); • possibilist fallacies (a favorite among conspiracy theorists who attempt to demonstrate that a factual statement is true or false by establishing the possibility of its truth or falsity. An argument where ‘‘it could be’’ is usually followed by an unearned ‘‘therefore, it is.’’); • slippery slope arguments or fallacies (a series of increasingly dramatic consequences is drawn from an initial fact or idea); • begging the question (the truth of the conclusion is assumed by the premises); • straw man arguments (the arguer mischaracterizes an argument or theory and then attacks the merits of their own false representations); • appeals to pity or force (the argument attempts to persuade people to agree by sympathy or force); • prejudicial language (values or moral goodness, good and bad, are attached to certain arguments or facts); • personal attacks (ad hominem; an attack on a person’s character or circumstances); • anecdotal or testimonial evidence (stories that are unsupported by impartial observation or data that is not reproducible); • post hoc (after the fact) fallacies (because one thing follows another, it is held to cause the other); • the fallacy of the appeal to authority (the argument rests upon the credentials of a person, not the evidence). Despite the fact that some primary sources can contain false information or lead readers to false conclusions based on the ‘‘facts’’ presented, they remain an invaluable resource regarding past events. Primary sources allow readers and researchers to come as close as possible to understanding the perceptions and context of events and thus to more fully appreciate how and why misconceptions occur. xxviii INFECTIOUS DISEASES: IN CONTEXT