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Emerging and Re-emerging Infectious Diseases

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Introduction and Goals

Introduction

Despite remarkable advances in medical research and treatments during the 20th century, infectious diseases remain among the leading causes of death worldwide for three reasons: 1) emergence of new infectious diseases; 2) re-emergence of old infectious diseases; and 3) persistence of intractable infectious diseases. Emerging diseases include outbreaks of previously unknown diseases or known diseases whose incidence in humans has significantly increased in the past two decades. Re-emerging diseases are known diseases that have reappeared after a significant decline in incidence. Within the past two decades, innovative research and improved diagnostic and detection methods have revealed a number of previously unknown human pathogens. For example, within the last decade, chronic gastric ulcers, which were formerly thought to be caused by stress or diet, were found to be the result of infection by the bacterium Helicobacter pylori.

New infectious diseases continue to evolve and "emerge." Changes in human demographics, behavior, land use, etc., are contributing to new disease emergence by changing transmission dynamics to bring people into closer and more frequent contact with pathogens. This may involve exposure to animal or arthropod carriers of disease. Increasing trade in exotic animals for pets and as food sources has contributed to the rise in opportunity for pathogens to jump from animal reservoirs to humans. For example, close contact with exotic rodents imported to the United States as pets was found to be the origin of the recent U.S. outbreak of monkeypox, and use of exotic civet cats for meat in China was found to be the route by which the SARS coronavirus made the transition from animal to human hosts.

In addition to the continual discovery of new human pathogens, old infectious disease enemies are "re-emerging." Natural genetic variations, recombinations, and adaptations allow new strains of known pathogens to appear to which the immune system has not been previously exposed and is therefore not primed to recognize (e.g., influenza). Furthermore, human behavior plays an important role in re-emergence. Increased and sometimes imprudent use of antimicrobial drugs and pesticides has led to the development of resistant pathogens, allowing many diseases that were formerly treatable with drugs to make a comeback (e.g., tuberculosis, malaria, nosocomial, and foodborne infections). Recently, decreased compliance with vaccination policy has also led to re-emergence of diseases such as measles and pertussis, which were previously under control. The use of deadly pathogens, such as smallpox or anthrax, as agents of bioterrorism is an increasingly acknowledged threat to the civilian population. Moreover, many important infectious diseases have never been adequately controlled on either the national or international level. Infectious diseases that have posed ongoing health problems in developing countries are re-emerging in the United States (e.g., food- and waterborne infections, dengue, West Nile virus).

Research Plans and Priorities

In response to the threat of emerging and re-emerging infectious diseases, NIAID has developed a strategy for addressing these issues through targeted research and training. That strategy, which was initially outlined in the Institute's 1996 document, "A Research Agenda for Emerging Infectious Diseases," was updated in the 2008 NIAID strategic plan, "NIAID: Planning for the 21st Century." In May 2001, NIAID released the "NIAID Global Health Research Plan for HIV/AIDS, Malaria, and Tuberculosis." This document outlined the Institute’s plans for the next decade for diagnosing, treating, and preventing these three infections and also laid out a plan for enhancing research capacity in-country.

NIAID research plans and priorities include

  • Strengthening basic and applied research on the pathogen, host, and environmental factors that influence disease emergence
  • Using knowledge of pathogen, host, and environmental interactions to enhance our ability to predict and prevent conditions that lead to human disease
  • Supporting development of diagnostics, vaccines, and therapies necessary to detect and control infectious diseases
  • Supporting sequencing and post-genomics research of emerging infectious disease agents and animal vectors to reveal genetic basis for microbial/vector evolution, adaptation, and pathogenicity
  • Developing new strategies to control diseases that are re-emerging due to drug or insecticide resistance
  • Identifying better control strategies for intractable infectious diseases that continue to challenge global health
  • Maintaining and developing the national and international scientific expertise required to respond to future health threats by supporting research and training programs

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Last Updated March 10, 2010