Emerging and Re-emerging Infectious Diseases: An Update

Emerging and Re-emerging Infectious Diseases: An Update

By Michelle Gardner

At the dawn of the 20th century, cancer, heart disease, kidney disease, cirrhosis, pneumonia, cholera, diphtheria, tuberculosis (TB) and influenza were relentless killers. Survival was purely a crapshoot.1

By the end of the 20th century, vaccines had conquered many of man's most dreaded plagues, eliminating smallpox and all but wiping out mumps, measles, rubella, whooping cough, diphtheria and polio, at least in the developed world.2

But the public health system that had become the envy of the world has fallen into disrepair. The drive to lower healthcare costs and the reforms of managed care have taken their toll. Government laboratories are running out of funding and equipment; emergency rooms are running out of staff and beds; emergency preparedness plans have become moldy and outdated. Many of the labs at the Centers for Disease Control and Prevention (CDC) are crumbling.3

An Executive Summary

Emerging diseases are those whose incidence in humans has increased in the past two decades, and re-emergence is the reappearance of a known disease after a significant decline in incidence.4 The magnitude of the problem is illustrated by the appearance of several new pathogens causing disease of marked severity, such as the human immunodeficiency virus (HIV) and other retroviruses, arenaviruses, Hantaviruses and the Ebola virus. Old pathogens such as cholera, plague, dengue hemorrhagic fever and yellow fever have re-emerged and are having considerable impact in the Americas.

Just 50 years ago, many people believed the battle between humans and infectious disease was over, with humankind the winner. But globally, infectious diseases remain the leading cause of death, and they are the third leading cause of death in the United States.5 Understanding the infectious cycle is critical in order to identify accessible targets for control strategies. For example, person-to-person transmission may be inhibited by proper hygiene and sanitary conditions and education. Vector borne diseases may be prevented by control measures that either kill the vector or prevent its contact with humans. Infection by a pathogen or development of a pathogen within a host may be prevented by vaccination. Finally, drugs may be used to prevent infection or suppress the disease process.

Six major factors that contribute to the emergence of infectious disease are: human demographics and behaviors; advances in technology and industry; economic development and changes in land use patterns; dramatic increases in international travel and commerce; microbial adaptation and change; and the breakdown of public health measures.9

The Pan American Health Organization (PAHO)'s regional plan of action provides guidance in addressing specific problems and in implementing regional and subregional measures for the prevention and control of infectious diseases.4 The plan's four goals are:

1. Strengthening regional surveillance networks for infectious diseases in the Americas.

2. Establishing national and regional infrastructures for early warning of and rapid response to infectious disease threats through laboratory enhancement and multidisciplinary training programs.

3. Promoting the further development of applied research in the areas of rapid diagnosis, epidemiology and prevention.

4. Strengthening the regional capacity for effective implementation of prevention and control strategies.

With programs, best practices and guidelines in place to defend against emerging and re-emerging infectious diseases, those wanting to get a handle on emerging infectious diseases (EIDs) ask a valid question: Where do you start?

"The traditional approach has been biomedical," says David Fidler, professor of law and Ira C. Batman Faculty Fellow, Indiana University School of Law, Bloomington, Ind. "You get, 'Here is the disease, here is the microbe that causes it, here is the antibiotic we have. Go get 'em!' To a large extent, that worked for a number of decades, but chronic diseases and infectious diseases have moved back up to the No. 3 cause of death in America."

As Fidler observes, the microbes aren't going to sit still. "If we do not continue to spend money on innovation, the arsenal we believe we have is going to dwindle in effectiveness. It is the way of the microbial world -- there will eventually be resistance to outside intervention."

Keeping a Close Watch

The ability to spot new disease outbreaks, diagnose them properly and get word out on the medical wires is central to managing crises like anthrax and more routine problems like Lyme disease, tuberculosis and influenza. The most important step toward improvement is upgrading the public health system's surveillance powers. The CDC relies on a national network of sentinel doctors to do this kind of monitoring during flu season and uses a similar system of local labs and DNA fingerprinting to track food-borne illnesses. Cities and states have physician-alert programs that do the same job.3

Public health surveillance is the ongoing, systematic collection, analysis, interpretation and dissemination of health data, including information on clinical diagnoses, laboratory-based diagnoses, specific syndromes, health-related behaviors and other indicators related to health outcomes.7 The first goal of the CDC's Preventing Emerging Infectious Diseases plan is surveillance and response, for which the objectives call for strengthening infectious disease surveillance and response in the United States and internationally, and improving methods for gathering and evaluating surveillance data.

"Surveillance is a long process," says Rana A. Hajjeh, M.D., chief of the epidemiology unit at the CDC in Atlanta. "You need to be sure there is a basic infrastructure in the state where you are doing the surveillance. Traditionally, we have relied on passive reporting in which physicians should know what is to be reported to the health department. Unfortunately, physicians don't have time, unless it is TB or sexually transmitted diseases (STDs), where tracing of contacts needs to be done by the health department."

Implementation of the CDC's plan is expected to produce (in part) a nationwide network for surveillance and response to ensure the prompt identification of EIDs; intensive population-based surveillance and research programs in at least 10 areas of the United States; and a global system for surveillance and response to infectious agents that are resistant to antimicrobial drugs.7

Look at it This Way

Fidler's 1997 article, "The Globalization of Public Health: Emerging Infectious Diseases and International Relations," explains how the processes of globalization have altered traditional distinctions between national and international public health. Most public health experts agree that the distinction between national and international public health is no longer relevant because globalization has enabled pathogenic microbes to spread illness and death globally, with unprecedented speed. The blurring distinction between national and international health suggests that the forces of globalization are undermining the sovereign state's ability to prevent and control infectious diseases.6

"When I looked into this issue from an international lawyer's perspective, it seemed that the public health community already had a conception of public health in a global sense, but it tended to focus on things biomedically rather than politically," says Fidler.

As Fidler researched the role of international law in global public health, three things became apparent: international lawyers historically had not been interested in public health; public health professionals had not been interested in international law; and international relations specialists were not interested in international law or public health. Why the concern over this interdisciplinary gap?

"People are starting to talk about the political, socioeconomic and legal issues surrounding public health," says Fidler. "As we come to grips with HIV/AIDS and other emerging infections, people have realized that you have to have this multidisciplinary perspective. It allows a more comprehensive perspective when you use the three frameworks, or tweak traditional biomedical approaches to deal with today's global problems."

The World Health Organization (WHO) asserts that infectious diseases represent a global crisis that requires a coordinated international approach. The strategies crafted to date by the WHO and the United States to deal with emerging infectious diseases are predominantly blueprints for cooperation among states and represent a call for the internationalization of responses to a problem caused by globalization.6

International travel and trade are often cited as factors in the problem of emerging infectious diseases. "The CDC is working with travel medicine clinics to increase awareness about infections," says Hajjeh. "Research projects monitor infections that could come from outside the country." Adds Fidler, "You don't react out of fear or irrationality, you react out of science and public health principles when responding to travelers or trade that come from countries suffering from outbreaks."

Money Talks, But in What Language?

Hajjeh emphasizes that, as a whole, officials need to devote more funds and research to improve the diagnostic methods for infectious diseases. "We need to look into more sensitive methods, especially molecular techniques, to identify these organisms and do a better job diagnosing them," she says. "Our tests are not good enough to diagnose things we know, so what about things we don't know? Only 30 percent of our unexplained cases became explained. We need to do more work with the surveillance infrastructure in the state health department, and there is progress being made in improving diagnostics."

With four deaths and 12 people sick from anthrax, President Bush is proposing to fund bioterrorism preparedness in the United States with $5.9 billion in fiscal year 2003 alone. "What is going on in the rest of the world?" asks Fidler. "Millions of deaths occur each year from TB, malaria and HIV/AIDS, not to count (the other EIDs). Our contribution to the global fund is a total of $200 million. That's not even on a fiscal year basis. The United States should spend resources on bioterrorism because it is a serious threat. But compare that with the United States' interest in infectious diseases in largely poor countries and you see that we don't buy the argument that HIV/AIDS in sub-Saharan Africa is a national security threat. Where are we going to spend money for new scientific research? It is on a vaccine for anthrax or smallpox, neither of which is a public health concern in the general sense of the word. What are we doing about new antibiotics for Staphaureus or enterococci? That's what is killing people in hospitals. Where is the big money for that?"

Defense against EID threats

Developed countries have regulations that help protect the general public from infectious diseases.5 Public health measures typically involve eliminating the pathogen from its reservoir or from its route of transmission. Those measures include ensuring a safe water supply, effectively managing sewage treatment and disposal, and initiating food safety, animal control and vaccination programs.

As a preventable social burden, suffering from infectious diseases -- and the social consequences -- should not be happening.8 We are the first generation ever to have the means of protecting the world from the most deadly and common infectious diseases. We possess the knowledge, drugs, vaccines and commodities to prevent or cure tuberculosis, malaria, HIV, diarrhoeal diseases, pneumonia and measles practically anywhere on our planet. Immunization campaigns have eradicated smallpox, are on the verge of eradicating polio, and are rapidly decreasing deaths caused by measles. Vaccines have greatly reduced illness and death during the last 30 years, but the highest burden diseases remaining among the poor (such as TB, malaria and HIV) cannot currently be prevented with vaccines. Fortunately, other low-cost treatments and preventive measures are available for fighting these diseases.

Still, money for research tends to be based on politics, not epidemiology. "It is raw fear," says Fidler. "Fear and terror have revolutionized the landscape of public health. What are the long-term implications of dealing with this, even on the infectious disease side? Public health professionals hope for gigantic spillover effects so the public health system can be put back together after it has been incrementally dismantled and not funded for decades. Before the anthrax attacks, we would talk about the public health infrastructure and nobody knew what we were talking about. Now these obscure discussions are politically important. The Commission on Macroeconomics and Health's appeal for billions of dollars from developed countries is overshadowed by the bioterrorism fear at home. The rest of the world's infectious diseases have become even less important and that is frightening."

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