Threat

Threats to the public health have captured the attention of a broad community including writers of fiction, centers of academic research, and the distinguished members of the Institute of Medicine. Episodes of illness due to food-borne pathogens and the re-emergence of tuberculosis are representative of threats to the public health in which the ability to detect and identify pathogenic organisms more quickly, accurately, and routinely are desperately needed.

In addition to specific emerging diseases, four aspects of the evolution of modern disease warrant particular attention:

• emergence of long-latency disease, particularly Human Immunodeficiency Virus (HIV)
• eruption of epizootic and zoonotic disease as a result of environmental encroachment
• global transmission of disease into virgin populations by international travel
• development of antibiotic-resistant or antibiotic-dependent variants of heretofore common pathogens.

Long Latency Disease

In their report on emerging diseases, the Committee on Emerging Microbial Threats to Health of the Institute of Medicine emphasizes the importance of global disease surveillance as a critical tool in anticipating the threat to U.S. public health from emerging—and re-emerging—disease. In some cases, particularly in cases of highly lethal but long-latency, asymptomatic disease such as HIV, clinical diagnostic surveillance may not be possible until a global crisis is in full bloom. In cases such as these, new technologies for the surveillance of the pathogen organisms themselves may be required to avert catastrophe. Such technologies, and the protocols for their effective use, are beyond the reach of policy makers and health care providers today, but should be on the whiteboards of research planners.

Zoonoses from Environmental Encroachment

Completion of the Aswan dam in Egypt in the late 1970s and the Diama dam in Senegal in the 1980s created breeding sites for mosquitoes carrying Rift Valley fever, causing epidemics where the disease had not occurred before. Occurrence of Lyme disease in the United States and Europe follows reforestation and the resultant repopulation with tick-infested deer. The ultimate reservoir for the filovirus, Ebola, has not yet been identified, but epizootic or zoonotic transmission are almost certainly responsible for outbreaks of the disease.

As was the case for long-latency disease, clinical surveillance is critical to determining when a microbial population has migrated to a previously uninfected region. However, such surveillance may not allow sufficient opportunity between discovery of a threatening pathogen and formulation and execution of a response. Boundaries between man and nature are relatively well-defined in time and geography. Environmental survey technologies are needed. These could be used to detect pathogens when boundaries shift, releasing pathogens into a virgin population. These technologies would signal the need for intervention or mitigation.

International Travel

International travel offers an efficient mechanism for importation of disease from well beyond local populations. Patients can acquire disease in remote parts of the globe. Within hours or days, patients present an array of symptoms that are unfamiliar to local physicians or that can be confused with pathogens that are more common. Failure of physicians to accurately diagnose highly contagious, exotic diseases will put others at risk with whom the patient comes in contact. Under the worst circumstances, diagnostic failure could result in epidemic catastrophe. Limited resources ranging from public health infrastructure in the United States to epidemiologists familiar with "exotic" infectious diseases in the field make the challenge of successful diagnosis even greater.

Antibiotic Resistance and Dependence

One of the factors that contribute to the emergence and re-emergence of disease is the ability of organisms to evolve resistance to the antibiotics used to treat them. Some organisms have developed resistance to a suite of the most commonly prescribed antibiotics, making antibiotic therapy difficult to administer effectively. Among the common pathogens that have developed resistant strains are tuberculosis, streptococcus A and C, pneumococcus, staphylococcus, and enterococcus bacteria. For some of these pathogens, only the antibiotic vancomycin continues to prove effective. Mutation and adaptation of disease organisms are limiting the effectiveness of one of our most powerful disease fighting tools. Increased attention to prudent use of antibiotics--such as emphasis on the delivery of the full regime of antibiotic prescriptions and evaluation of the use of antibiotics in agriculture--is crucial, but may be too late in coming.

Response

The first and most powerful step to mitigating the threat to public health from these developments is information. Clinical diagnostic surveillance of disease occurrence is critical to limit the potential for catastrophe. However, clinical surveillance identifies the spread of disease in process. Therefore, even if a perfect system of international clinical surveillance were formulated and implemented, it would not be enough. If the technology and protocols could be developed, environmental pathogen surveys could supplement clinical surveillance to provide an opportunity for preemptive intervention.

Beyond recognizing the phenomenon and intervening where possible before widespread outbreak of disease, responding to the occurrence of infectious disease on a large scale requires attention of policy makers, health care providers, scientists, and industry.

References and Links

• Emerging Infections: Microbial Threats to Health in the United States , Joshua Lederberg, Robert E. Shope, and Stanley C. Oaks, Jr., Editors; Committee on Emerging Microbial Threats to Health, Institute of Medicine.
• "Superbug that eats antibiotics turns cure into killer," Jeremy Laurance, The Times of London, December 6, 1996.

• Vancomycin-dependent Enterococcus faecalis, The Lancet, Volume 348, Number 9041, 12/7/96.