THE TWENTY-FIRST CENTURY

The twenty-first century reveals new horizons, but also new problems. In greater numbers than ever, goods and people travel the world. There is unprecedented physical mobility—travel and migration from villages to cities and country to country—and interconnectedness. However, the benefits of physical mobility and interconnectedness 

are accompanied by risks. Diseases such as AIDS remind us that nothing is regional, local, or limited in its reach: con­tagious illness has a worldwide arena.

The challenges of maintaining health and well-being in this global community are increasingly apparent. The in­advertent introduction of pathogens poses an unrelenting threat to public health, as does the deliberate use of micro­organisms as weapons (see Chapter 18 for a discussion of bioterrorism and emerging global infectious diseases). In February 2003, the viral respiratory illness named severe acute respiratory syndrome (SARS) by the World Health Organiza­tion was first recognized in China.⁸ In the next few months, the illness swept through parts of Asia and spread to more than two dozen countries in North America, South America, and Europe. The disease was characterized by rapid onset and variable severity, ranging from mild illness to death. The prevention of SARS was a particular challenge because pre­ventive interventions (e.g., vaccines and antibiotics) were unavailable. Containment became a global collaboration, with public health authorities utilizing isolation and quar­antine to focus delivery of health care to people who were ill and to protect healthy people from getting sick. During the February to July outbreak, more than 8000 people world­wide became infected, and more than 900 died.

Commerce also is an integral part of the growing world community, bringing goods and services once un­obtainable into the global marketplace. Expanded inter­national trade also provides the vehicle for the unwitting introduction or transmission of disease. One such instance occurred in the spring of 2003 in the United States.⁹ A multistate outbreak of human monkeypox, first identified in the Democratic Republic of the Congo in 1970, was traced by investigators to pet prairie dogs. The prairie dogs became infected when they were housed or transported along with infected Gambian giant rats, dormice, and rope squirrels that were part of a shipment of small mammals from Ghana. Spread of nonindigenous zoonotic patho­gens to indigenous susceptible animal populations can be rapid and deadly. With such outbreaks lurks an additional danger—the potential for interspecies exchange, includ­ing between humans and animals such as pets.

The widespread distribution of infected and potentially infected animals allowed epizootic spread of monkeypox through several states before effective interventions could be put into place. One of the challenges to the world health community will be to study the role of international travel and commerce in the emergence of infectious diseases through the dissemination of pathogens and their vectors throughout the world and then to develop long-term strate­gies of surveillance and intervention with the ultimate goal of curtailing their occurrence.

In 1976, the World Health Organization (WHO) actu­ally succeeded in eliminating smallpox from the face of the earth.¹⁰ This triumph gave substance to the idea that other infections, like measles, also might disappear if suf­ficient efforts were directed at worldwide campaigns to isolate and cure them. However, new infectious diseases, such as Lyme disease and Legionnaire's disease, and new forms of old diseases, such as resistant strains of tubercu­losis and malaria, have emerged and are readily spread

worldwide. The powerful interventions used to fight these infections have had the unexpected effect of accelerating their biologic evolution and making them impervious to one after another form of chemical attack.

Pathogens also can be introduced into the food chain and travel worldwide. The discovery that beef from cattle infected with bovine spongiform encephalopathy (BSE) may be the source of Creutzfeldt-Jakob disease led many countries to ban beef products from the United Kingdom when BSE was found to be prevalent in English herds. The introduction of such pathogens can be the result of igno­rance, carelessness, or greed. Tobacco is a product that serves as a pathogen. In a quest for ever-increasing profits, the tobacco industry created a demand for its product by artificially raising the nicotine content of cigarettes so as to increase their addictive potential. This was done with the knowledge of the health risks of tobacco products, thanks to experiments conducted by the tobacco companies' own medical scientists, but kept secret.

If there is a blueprint for future advances, it is in the genes. The twenty-first century is destined to be dominated by advances in genetics. With the mapping of the human genome comes hope of cure for some of the most dreaded crippling and fatal diseases. The mapping of the human genome also has posed new ethical dilemmas, for with it comes the potential to predict the future health of persons based on their genes. It soon may be possible to differenti­ate between persons who will develop certain debilitating diseases and those who will not.

Although advances in science and technology will continue to provide new treatments for many diseases, it has become apparent that there are more impressive re­wards to be had by preventing diseases from becoming es­tablished in the first place. Ultimately, maintaining health is more resource conservative and cost effective than re­lying on the treatment of disease. Many decades ago, we learned that even though the "magic bullets" such as anti­biotics had the ability to cure what was once considered incurable, much of our freedom from communicable dis­ease is due to clean water, efficient sanitation, and good nutrition. We have become increasingly aware of the im­portance of preventive measures against noninfectious conditions, especially cancer and coronary heart disease. There is no better way to prevent disease and maintain health than by leading a healthy life, and increasingly, it will be the individual who is responsible for ensuring a healthy passage through life.

In summary, Greek scholars were responsible for establish­ing the fundamentals of anatomy, physiology, and pathology that served as the earliest knowledge base for understanding health and disease. It was Hippocrates (460-377 BC) and his followers who laid the foundations of the clinical principles and ethics that grew into modern science. Although his belief that disease occurred when the four humors-blood, yellow and black bile, and phlegm-became out of balance was dis­proved, his approach to health that dictated plenty of healthy exercise, rest in illness, and a moderate, sober diet remains valid. Galen (ad 129-199) took the next major step, expand-

ing on Hippocratic doctrines and introducing experimentation into the study of healing. His work, gleaned through his role as physician to the emperors and gladiators of Rome and an­imal dissections, came to be regarded as the encyclopedia of anatomy and physiology and was considered infallible for almost 1400 years.

Significant challenges to long-held beliefs began with the work of Andreas Vesalius (1514-1564), professor of anatomy and surgery at Padua, Italy. His published work, On the Fabric [Structure] of the Human Body, showing how the parts of the body looked and worked, set a new standard for the under­standing of human anatomy. Other significant early contri­butions were made by scholars such as William Harvey (1578-1657), the English physician and physiologist, who in his book, On the Motion of the Heart and Blood in Animals, provided a physiologic framework for the circulation of blood; Anton van Leeuwenhoek (1632-1723), the Dutch lens maker who refined the microscope and set the stage for the era of cellular biology; and Edward Jenner (1749-1823), the English country physician who conducted the first suc­cessful vaccination.

The nineteenth century was a time of major discoveries that paved the way for understanding infectious diseases. Sig­nificant contributions were made by such scientists as Joseph Lister, the English surgeon who concluded that microbes caused wound infections; German bacteriologist Robert Koch, who discovered the anthrax bacillus, thus identifying for the first time a microorganism and the illness it caused; and French chemist and microbiologist Louis Pasteur, who developed the technique of pasteurization. Perhaps the most notable techni­cal innovation of the century was the discovery of X rays by German physicist Wilhelm Röntgen.

The scientific undertakings and discoveries of the twentieth century were revolutionary. In 1910, Paul Ehrlich introduced chemotherapy, and in 1928, Sir Alexander Fleming discovered the first antibiotic as he studied the relationship between bac­teria and the mold Penicillium. Diseases that had once been fatal or crippling were managed or prevented by new ad­vances, such as the discovery of insulin by Sir Frederick Banting and Charles Best in 1922 and the development of the polio vaccine by Jonas Salk in 1953. Technical innovations set the stage for new surgical techniques. The creation of the heart-lung machine by American surgeon John Gibbon paved the way for coronary bypass surgery and the first successful heart transplantation in 1967, which was performed by Christiaan Barnard, a South African surgeon. Other important advances included kidney dialysis, oral contraceptives, the CAT scanner, and coronary angioplasty. Public health programs also were re­sponsible for greatly affecting the health of populations, such as those dedicated to increasing vaccination, improving sani­tation of water and waste disposal, and identifying health risks.

Knowledge about the influence of heredity on health and disease originated with Charles Darwin's (1809-1882) evolu­tionary theories about inherited traits and with Gregor Mendel's (1822-1884) theories on the segregation of traits, which laid the groundwork for establishing the chromosome as the struc­tural unit of heredity. In the early 1950s, geneticist James Watson of the United States and British biophysicists Francis Crick and Maurice Wilkins presented their findings on the double-helical structure of DNA.

The twenty-first century is predicted to be a time of great advances in the field of genetics, already evidenced by the substantial mapping of the human genome that has taken place. Scientists look to genetic research to provide advances that not only will predict who may develop disease but also will provide new treatments for those diseases. However pro­mising future advances may appear, it is readily apparent that prevention is an equally important tool in maintaining health.