|
|
|
|
CIAO DATE: 07/06
D.A. Henderson, M.D., is a professor of medicine and public health at the University of Pittsburgh. He is resident scholar at the Center for Biosecurity, an adviser to the U.S. Department of Health and Human Services on public health emergency preparedness, and formerly chief medical officer for smallpox eradication of the World Health Organization (WHO).
During the past 20 years, a surprising number of new infectious diseases have been discovered, some afflicting only one or a few countries, while AIDS has spread inexorably to eventually become a global epidemic and the fourth leading cause of death in the world. Others have also appeared—in all, at least 30 new diseases. Many more may be anticipated because over recent decades, there have been dramatic demographic, technological, and social changes that have markedly altered the potential for disease transmission, and these changes are progressing exponentially.
Of special concern today is the global threat of pandemic avian influenza, a new type of influenza virus that poses a serious threat to every country. The avian influenza threat clearly shows how advances in global technology may help spread diseases, but it also demonstrates how global cooperation may lead to effective countermeasures. Influenza outbreaks normally recur every year throughout the world. Although these are capable of causing severe illness and death in the elderly and those with chronic lung or heart disease, most persons experience little more than fever and respiratory symptoms for a week or so. About every 30 years, however, a new and different strain of influenza has emerged and spread across the world, causing widespread epidemics, known collectively as a pandemic.
The Bird Flu Threat
One of the most serious pandemics occurred in 1918, when a new type of influenza virus arose that proved to be much more lethal than ever before. It resulted in the deaths of at least 50 million persons worldwide. Concerns about the possibility of an equally serious pandemic were reawakened in 1997 when a new, more threatening strain of influenza (now identified as the H5N1 strain of avian influenza) was discovered in Hong Kong. It was exceptionally lethal for poultry, especially chickens, but it also claimed 18 human victims, of whom six died. Never before had an influenza strain caused such a high human death rate. The cases all occurred among those working with sick chickens.
Fortunately, at that time, the disease did not spread from human to human. Public health authorities quickly destroyed millions of chickens, and the virus seemed to have disappeared. Unfortunately, six years later it reemerged once again in chickens and soon began to spread throughout Southeast Asia. Tens of millions of chickens have died from the disease or have been killed in attempts to control the further spread of the virus. Close to 150 human cases have occurred, almost half of which were fatal. Almost all patients had been in close contact with the sick birds or provided health care to one of the patients.
Wild fowl are now infected and, as a result of migration, the virus has spread to western Asia, Eastern Europe, and Africa. As the disease continues to spread, there is justifiable concern that, at any time, the virus might change its character and begin to spread from person to person. Because of today's volume of air passenger traffic, it is certain that it would spread worldwide within weeks.
A vaccine will be needed to protect humans against the disease. However, the vaccine, to be effective, must closely resemble the virus that is capable of spreading from person to person, though that viral strain does not yet exist, as far as scientists know. Thus, an intensive international effort involving laboratories, public health staff, and industry is under way to obtain, as quickly as possible, the virus as soon as it begins to spread from person to person, and to use new approaches in vaccine production that will permit large quantities of vaccine to be produced rapidly.
The Need for Global Cooperation
The influenza threat aptly illustrates the need for greater international cooperation to discover and counter disease threats, wherever they may occur. Such cooperation is needed more urgently today than at any time in history. In the microbial world, countless species are continually multiplying at astronomical rates, each species mutating, adapting, and changing to assure its own survival. Inevitably, from time to time, microbes with different characteristics arise, some highly lethal to humans and some with a capacity to grow and to spread readily. In agrarian societies with scattered populations and small towns or villages, new agents had much less of a chance of being transmitted from person to person, and soon they would die out. Even if significant spread of a new disease did occur in one area or country, further dissemination often was curtailed because of the limitations of travel. The ease with which we travel the globe may spread the most threatening diseases, but advances in communications may also serve to facilitate cooperation to find cures—a global health connection.
Today, cases and outbreaks of disease, whatever their cause and wherever they may occur, pose a threat to the health of people throughout the world. No major city in the world is more than 36 hours distant from any other. In 2003, some 642 million international air travelers disembarked at 750 different airports in 135 countries. Once-common border controls and inspections have proved to be of no value in the prevention of disease, as was clearly shown during the 2003 SARS epidemic. More than 35 million passengers were screened with the intent of quarantining those with fever. No cases were found. If travelers had been infected, they were most likely in the silent, incubation phase of illness and could not have been identified, whatever screening measures had been employed. We are now experiencing population movement of a magnitude and speed such as has never before been witnessed.
The likelihood of new microbial agents gaining a foothold is greatly enhanced by the rapid growth of urban populations. As recently as 50 years ago, there were only two cities with populations of more than 7 million persons (New York and London); only 20 percent of the world's population lived in urban areas. Today, there are 30 cities with populations of more than 7 million, and seven of these, in fact, have populations larger than 15 million. Many such cities are in tropical and subtropical areas where crowding, malnutrition, poor sanitation, and environmental pollution are predominant features. This is fertile soil indeed for establishing a new disease.
Another major influence in disease dissemination is the industrialization and internationalization of food supplies. Only a few decades ago, most foodstuffs were grown locally on small farms and preserved or prepared for commercial use in small establishments, few of which engaged in international trade. If contamination occurred at any point, few persons were affected. With larger-scale food production and processing and the potential for refrigerated and air shipment of food, contamination at any point in the food production chain can result in massive epidemics extending across many countries. A small illustration of this was a severe diarrhea epidemic caused by an organism called shigellosis in August 2004. It resulted from contamination in a United States airline food preparation kitchen. In all, 241 cases were specifically identified, but it was estimated that 9,000 cases had actually occurred on 219 different flights going to 24 states and four foreign countries.
A seldom considered but major factor facilitating the spread of disease is the extensive proliferation of hospitals, especially in countries and areas where economic resources are taxed and professionally trained personnel are sparse. Many such hospitals have no provision for the isolation of contagious patients and little or no equipment to permit adequate sterilization of needles and syringes as well as surgical instruments. Blood-borne diseases may result, and, indeed, this factor has been an important contributor to the spread of AIDS in some nations. At the same time, it is customary in such medical care settings for large numbers of family and friends from villages and towns scattered over a very wide area to visit the patient. In consequence, sudden explosive epidemics of disease extending over a wide area are not uncommon. Recent experience has shown that hospitals have been the primary site for epidemic transmission of measles and hemorrhagic diseases such as those caused by the Lassa, Ebola, and Marburg viruses.
In this global age, the health of every human being on the planet has become relevant to the health of every other. We have yet to fully grasp the implications of this fact, although both AIDS and avian influenza are proving to be important in communicating this message. There is a need to attack infectious disease problems wherever they occur. An epidemic today in the most remote areas of Africa or the Americas, for example, can tomorrow result in cases and perhaps outbreaks almost anywhere else in the world. In practical terms, the May 2005 adoption of updated WHO International Health Regulations is a positive step toward undertaking the shared research and development necessary to deal with disease problems wherever they occur, and in fashioning effective international networks for research and education such that important findings and observations can be more rapidly and effectively transmitted and applied.
The opinions expressed in this article do not necessarily reflect the views or policies of the U.S. government.