Global Microbial Threats in the 1990s
Thirty years ago, the threat of infectious diseases appeared to be receding. Modern scientific advances, including antibiotic drugs, vaccines against childhood diseases, and improved technology for sanitation, had facilitated the control or prevention of many infectious diseases, particularly in industrialized nations. The incidence of childhood diseases such as polio, whooping cough, and diphtheria was declining due to the use of vaccines. In addition, American physicians had fast-acting, effective antibiotics to combat often fatal bacterial diseases such as meningitis and pneumonia. Deaths from infection, commonplace at the beginning of the twentieth century, were no longer a frequent occurrence in the United States. Meanwhile, in other parts of the world, chemical pesticides like DDT were lowering the incidence of malaria, a major killer of children, by controlling populations of parasite-carrying mosquitoes.
As it turned out, our understandable euphoria was premature. It did not take into account the extraordinary resilience of infectious microbes, which have a remarkable ability to evolve, adapt, and develop resistance to drugs in an unpredictable and dynamic fashion. It also did not take into account the accelerating spread of human populations into tropical forests and overcrowded mega-cities where people are exposed to a variety of emerging infectious agents.
Today, most health professionals agree that new microbial threats are appearing in significant numbers, while well-known illnesses thought to be under control are re-emerging. Most Americans are aware of the epidemic of the acquired immunodeficiency syndrome (AIDS) and the related increase in tuberculosis (TB) cases in the United States. In fact, there has been a general resurgence of infectious diseases throughout the world, including significant outbreaks of cholera, malaria, yellow fever, and diphtheria. In addition, bacterial resistance to antibiotic drugs is an increasingly serious worldwide problem. Furthermore, the number of people infected with the human immunodeficiency virus (HIV) that causes AIDS is increasing in many countries and may reach 40 million by the year 2000. Most recently, Ebola virus, which causes an often fatal hemorrhagic illness, has appeared again in Africa, and a formerly unknown virus of the measles family that killed several horses in Australia also infected two men, one of whom died.
New diseases have also appeared within the United States, including Lyme disease, Legionnaires' disease, and most recently hantavirus pulmonary syndrome (HPS). HPS was first recognized in the southwestern United States in 1993 and has since been detected in more than 20 states and in several other countries in the Americas. Other new or re-emerging threats in the United States include multidrug-resistant TB; antibiotic-resistant bacteria causing ear infections; pneumonia; meningitis; rabies; and diarrheal diseases caused by the parasite Cryptosporidium parvum and by certain toxigenic strains of Escherichia coli bacteria.
The reasons for the sharp increase in incidence of many infectious diseases - once thought to be under control - are complex and not fully understood. Population shifts and population growth; changes in human behavior; urbanization, poverty, and crowding; changes in ecology and climate; the evolution of microbes; inadequacy of public health infrastructures; and modern travel and trade have all contributed. For example, the ease of modern travel creates many opportunities for a disease outbreak in remote areas to spread to a crowded urban area. Human behavioral factors, such as dietary habits and food handling, personal hygiene, risky sexual behavior, and intravenous drug use can contribute to disease emergence. In several parts of the world, human encroachment on tropical forests has brought populations with little or no disease resistance into close proximity with insects that carry malaria and yellow fever and other, sometimes unknown, infectious diseases. In addition, local fluctuations in temperature and rainfall affect the number of microbe-carrying rodents in some areas. Finally, in many parts of the world there has been a deterioration in the local public health infrastructures that monitor and respond to disease outbreaks.
The costs of infectious diseases at home and abroad are staggering, and the cost-effectiveness of disease prevention has been demonstrated again and again. Every year, billions of dollars are lost in the United States in direct medical costs and lost productivity, due to intestinal infections, sexually transmitted diseases, influenza, and other viral, bacterial, or parasitic diseases. When diseases are controlled or prevented, tremendous savings can be achieved. For instance, a timely epidemiologic investigation in Washington State in 1993 led to the prompt recall of 250,000 hamburgers contaminated with E. coli O157, saving millions of dollars as well as preventing human suffering and death. Since smallpox was eradicated in 1977, the total investment of $32 million has been returned to the United States every 26 days. Based on the current rate of progress towards eradication of poliomyelitis, the World Health Organization predicts "global savings of half a billion dollars by the year 2000, increasing to $3 billion annually by the year 2015." Furthermore, every dollar spent on the vaccine against measles, mumps, and rubella, saves $21, while every dollar spent on the vaccine against diphtheria, tetanus, and pertussis saves $29. Clearly, public health measures that prevent or control infectious diseases are extremely cost-effective.
Today, two of the largest U.S. infectious disease health-care expenses are for the treatment of TB and AIDS. When the first cases of AIDS and drug-resistant TB were detected in the United States control measures were delayed, partly due to a lack of surveillance information. TB is an ancient disease, known throughout human history, that re-emerged in the United States in the late 1980s, sometimes in a drug-resistant or multidrug-resistant form. Government spending on infectious disease control had declined during the 1980s, and in 1986 the surveillance system for drug-resistant TB was discontinued. By 1993, multidrug-resistant TB had became a public health crisis and millions of federal dollars were necessary to control the emergency.
Unlike TB, AIDS is a newly emergent disease, unrecognized before the 1980s. AIDS might have been identified before it became established in the United States if a global surveillance system with the capacity to identify new diseases had been in place in the 1970s. As early as 1962, African doctors apparently witnessed cases of what was then known as "slim disease." Had the international community taken notice, epidemiologists might have gained a head start in learning how AIDS is transmitted and prevented, and many lives might have been saved.
Disease prevention is an investment in the young people of the world and in our collective future. Every year, an estimated four million infant and child deaths are prevented by vaccination and other preventive health measures, due to multilateral efforts. At the same time, many countries have dramatically strengthened their health-care delivery systems, even in the face of economic stagnation. On the other hand, the AIDS pandemic and the resurgence of malaria and TB are impeding economic development in many of the world's poorest countries.
The modern world is a very small place; any city in the world is only a plane ride away from any other. Infectious microbes can easily travel across borders with their human or animal hosts. In fact, diseases that arise in other parts of the world are repeatedly introduced into the United States, where they may threaten our national health and security. Thus, controlling disease outbreaks in other countries is important not only for humanitarian reasons. It also prevents those diseases from entering the United States, at great savings of U.S. lives and dollars. Moreover, U.S. support for disease investigations in other countries provides U.S. scientists with opportunities to bring U.S. capacity to focus on new pathogens like Ebola virus and consider how best to control, prevent, and treat them internationally before they arrive on our shores. Thus, U.S. interests are served while providing support to other nations.
Actively promoting the effort to develop an international partnership to address emerging infectious diseases is a natural role for the United States. American business leaders and scientists are in the forefront of the computer communications and biomedical research communities that must provide the technical and scientific underpinning for disease surveillance. The United States maintains more medical facilities and personnel abroad than any other country, in terms of both civilian and military, and public and private sector institutions. Furthermore, American scientists and public health professionals have been among the most important contributors to the international efforts to eradicate smallpox and polio. This position of leadership should be fostered.
Our earlier successes in controlling infections have bred complacency. Consequently, the component of the public health system that protects the public from infectious microbes has been neglected, both here and abroad, and its focus has narrowed. In the United States, federal, state, and local efforts to control communicable diseases are concentrated on a few targeted illnesses, with few resources allocated to address new or re-emerging diseases. This limits the ability of the U.S. medical community to detect and respond to outbreaks of newly emerging diseases, whether here or in foreign countries.
The challenge ahead outstrips the means available to any one country or to international organizations. The elimination of smallpox would not have been possible without a truly global effort. Similarly, multilateral leadership and resources propel the international program to eradicate polio. Both examples demonstrate the value to American citizens of resources invested in global disease prevention.
In addition, an effective global disease surveillance and response network will enable the United States to respond quickly and effectively in the event of terrorist incidents involving biological or chemical agents. The experience gained in controlling naturally occurring microbes will enhance our ability to cope with a biological warfare agent, should the need arise. The release of nerve gas in the Tokyo subway system in March 1995 has underscored our need to be well prepared to counteract deliberate attempts to undermine human health.
To address the growing threat of emerging infectious diseases the U.S. Government must not only improve its public health infrastructure, but also work in concert with other nations and international bodies, particularly WHO. The work and cost of protecting the world's people from infectious diseases must be shared by all nations. Some industrialized countries have already decided to devote substantial resources to a surveillance effort, and some less developed nations may also be ready to engage in an international effort that is so clearly in their own interests. President Clinton and the other leaders of the G7 nations recently endorsed 11 pilot projects of the Global Information Infrastructure at the Halifax Summit, including a project entitled, "Toward a Global Health Network." This project is designed to help public health institutions in their fight against infectious diseases and major health hazards. In addition, the World Health Assembly recently passed a resolution that focuses on national capacity building related to detecting and controlling emerging infectious diseases. The U.S. Agency for International Development (USAID), other donors, and the WHO, are continuing to assist developing countries in establishing disease prevention and control programs and to encourage the development of disease reporting systems.
Although international efforts must be coordinated to prevent global pandemics, disease surveillance is first of all the responsibility of each sovereign nation. However, individual governments may not only lack the means to respond but may also be reluctant to share national disease surveillance information, fearing losses in trade, tourism, and national prestige. Nevertheless, because the United States is widely respected as the world's foremost authority on infectious disease recognition and control, we do learn about most major disease outbreaks in other countries, although not always in an official or timely fashion. Individual doctors, laboratories, or ministries of health often seek United States assistance when they are confronted with a disease problem that they cannot solve. To ensure that we continue to be notified when an unusual outbreak occurs, we must encourage and support other countries' efforts in national disease surveillance and respond when asked for assistance. We must strive to develop a sense of shared responsibility and mutual confidence in the global effort to combat infectious diseases.
The effort to build a global surveillance and response system supports other foreign policy goals of the United States. Obviously, such a system will help protect the health of American citizens and of people throughout the world. In the post-Cold War period, a major objective of U.S. foreign policy is the promotion of political stability through sustainable economic development around the globe. Helping other countries to help themselves _ to improve the lives of their citizens, develop their economies, and find niches in the global economy _ is a major goal for U.S. foreign assistance. Healthy people are more productive and better able to contribute to their country's welfare.
Surveillance
At the present time, a formal system for infectious disease surveillance does not exist on a global scale. When a cluster of cases of a new disease occurs in a remote part of Africa, Eastern Europe, Asia, or the Americas, the international community may or may not learn about it. If a new disease of unknown cause occurs in a part of the world that lacks modern communications, it may spread far and wide before it is recognized and brought under control. In most cases, however, news of a major outbreak spreads informally. When international resources are successfully mobilized, assistance in diagnosis, disease control and prevention can be made available to local health authorities. Clinical specimens can be sent to a diagnostic "reference" laboratory to rule out known disease agents. Epidemiologists can be sent into the field to help investigate the source of the new infection and determine how it is transmitted. Public health officials can use this information to implement appropriate control measures. Once the infectious agent has been identified, which is often a difficult task, experimental scientists can start to develop diagnostic tools and treatments if the disease is carried by a previously unknown agent.
The elements of a global network for disease surveillance already exist but need to be strengthened, linked, and coordinated. For instance, many U.S. Government departments and agencies maintain or support field stations and laboratories in Africa, Asia, and the Americas that may be electronically linked to provide an initial framework for a network for global infectious disease reporting. In partnership with other countries and with WHO, this skeletal surveillance network could be expanded over time to include many international resources, including national health ministries, WHO Collaborating Centers, hospitals, and laboratories operated by other nations, and American and foreign private voluntary organizations.
Information technology is revolutionizing communications worldwide; this technology needs to be applied to disease control programs, not only to effectively monitor program performance and progress, but also to detect and report emerging problems.
Response
The process of response encompasses a multitude of activities, including diagnosis of the disease; investigation to understand its source and modes of transmission; implementation of control strategies and programs; research to develop adequate means to treat it and prevent its spread; and production and dissemination of the necessary drugs and vaccines.
The international community does not always have adequate resources to respond to localized disease outbreaks and control them before they can spread across borders. If an "old" disease re-emerges, there may be a need for epidemiologic investigations and/or for emergency procurement or production of medical supplies. If the disease is new, efforts will be needed to identify the causative microbe and determine how to stop its transmission. To make the best possible use of U.S. expertise and resources, it is necessary to establish clear lines of authority and communication among U.S. Government agencies.
Response to infectious disease outbreaks, whenever and wherever they occur requires international preparation and planning. A goal of the WHO is to assist each country to develop its ability to provide laboratory diagnosis of diseases endemic to its area and to refer specimens from suspected newly emergent or re-emergent diseases to an appropriate regional reference laboratory. To reach this goal, each country must train medical workers and laboratory technicians and supply them with appropriate equipment and diagnostic resources.
In addition, several international elements must be in place to provide the wherewithal for effective and timely disease control and prevention efforts. First, regional reference laboratories must be maintained to provide diagnostic expertise and distribute diagnostic tests. Second, an international communications mechanism must be made available to receive and analyze global disease surveillance information. Third, regional procedures should be instituted to facilitate the production, procurement, and distribution of medical supplies, including vaccines for disease eradication programs. Fourth, enhanced public education in simple health measures in both industrialized and developing countries is very important.
Through programs administered by USAID and other agencies, the United States has invested in assisting developing countries to establish disease prevention and control programs, trained thousands of individuals, and strengthened scores of institutions. As a consequence, developing country researchers are better prepared to solve their own disease problems and contribute to solving global ones. Strengthening this foundation will be critical to facilitating timely and effective responses to disease outbreaks and minimizing the impact of emerging disease threats.
Research
An effective system for disease surveillance and control is critically dependent on a strong and stable research infrastructure. Scientific studies of infectious agents and the diseases they cause provide the fundamental knowledge base used to develop diagnostic tests to identify diseases, drugs to treat them, and vaccines to prevent them. Traditionally, this has been an area of U.S. strength and international leadership. To meet the new challenges represented by emerging diseases, a strong research and training effort must be sustained and strengthened. The current level of support for research and training in laboratory and field work on infectious diseases, other than AIDS and TB, is very limited. To combat new diseases for which no treatments are available, it is essential to maintain an active community of well-trained epidemiologists, laboratory scientists, clinical investigators, behavioral scientists, entomologists, and public health experts ready and able to seek new solutions for disease threats. At the present time, many of the brightest young microbiologists in the United States are leaving the field, discouraged by the lack of jobs and research funds.
USAID, National Institutes of Health (NIH), and Centers for Disease Control and Prevention (CDC) support has fostered the capacity of less developed countries to identify and solve their infectious disease problems. Applied research in these countries is aimed at preventing disease transmission through control of insect and animal vectors, environmental factors, and behavior, and at evaluating new or improved therapeutic and preventive measures. In addition, the National Oceanic and Atmospheric Administration is developing tools to predict local changes in weather that effect the incidence of vector-borne diseases.
Training
Many research programs routinely incorporate training opportunities for graduate students and postdoctoral fellows. In addition, there is an urgent need to augment specialized training programs in such areas as the handling of hazardous microbes, public health management, and field epidemiology.
Work in partnership with other countries, with WHO, and with other international organizations to improve worldwide disease surveillance, reporting, and response by
Strengthen the U.S. capacity to combat emerging infectious diseases by
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