Current Status of the Field
Microorganisms are everywhere and are essential to the existence of life on our planet, although only a few are known to cause disease in humans. Several selected viruses and bacteria have become useful models for laboratory investigations.
Infectious diseases continue to constitute a serious global threat to human health and well-being, representing the leading cause of death worldwide and the third leading cause in the United States. Due to dramatic changes in society, technology, and the environment, plus the reduced effectiveness of previous approaches to disease control, the spectrum of infectious diseases is expanding.
Diseases once believed to be conquered are increasing, as pathogens evolve and spread and new agents are recognized. Surprisingly, some diseases not previously recognized as being infectious have been found to have a microbial etiology. The term "emerging infectious diseases" refers to these phenomena.
Major pathogens identified
Researchers have identified various major microbial pathogens in the last 20 years, including:
- E. coli O157 (hemorrhagic colitis)
- Human T-cell lymphotropic virus (HTLV, T-cell leukemia)
- Borrelia burgdorferi (Lyme disease)
- Staphylococcus toxin (toxic shock syndrome)
- Human immunodeficiency virus (HIV, AIDS)
- Helicobacter pylori (peptic ulcers, gastric cancer)
- Hepatitis C virus (HCV, hepatitis, liver cancer)
- Vibrio cholerae O139 (epidemic cholera)
- Sin Nombre hantavirus (pulmonary syndrome)
- HHV-8 (Kaposi's sarcoma).
Identifying these agents and their mechanisms of pathogenesis has highlighted the continuing importance of infectious diseases to the public health and the need to reassess old concepts of microbial disease causation. In addition, we must assume that additional agents remain to be identified.
There are numerous new challenges confronting microbiologists, virologists, and infectious disease experts. The widespread use and misuse of antimicrobial drugs has produced drug-resistant organisms, notably tuberculosis. Public water supplies and food products have been contaminated by infectious agents (e.g., Cryptosporidium, E. coli, hepatitis A virus), putting entire communities at risk. Travel and commerce have fostered the worldwide spread of pathogens, such as HIV, cholera, influenza, and West Nile virus.
We now recognize that emerging infections can affect persons in geographically dispersed areas, regardless of cultural or ethnic background or socioeconomic status. Concern over the possible use of infectious agents by bioterrorists also lurks in the background
The future holds many opportunities in the area of microbial pathogenesis. The genomic era is providing a growing number of complete microbial genome sequences. The next phase is to translate nucleic acid sequences into microbial functional activities. This knowledge will help us understand virulence genes, the basis of drug resistance, microbial effects on host cell functions, and the unique interactions of specific pathogens with their hosts. Such developments will eventually lead to the design and testing of new therapeutic and preventive strategies for human disease.
Novel, Safe Vaccines
Vaccines are the safest, most cost-effective and powerful tools for preventing infectious diseases. They have probably prevented more disease than any other modern medical intervention except sanitation. Effective vaccines have allowed us to eliminate smallpox from the earth, with the elimination of poliovirus soon to be achieved. Recent advances in molecular biology and immunology have created opportunities for the development of novel, safe vaccines. A current challenge is that the targets of contemporary vaccine efforts, such as HIV, may display considerable (and changing) antigenic diversity.
The variety of microbial agents, their complex life cycle strategies, and their often rapid evolution confront microbiologists with fascinating and challenging diversity. The fundamental nature of viruses dictates their obligatory interactions with host cells and seizure of host cell functions. These inherent properties have made viruses extraordinary tools with which to probe the molecular basis of cellular processes, ranging from transcriptional regulation and tumor suppressor genes to signal transduction pathways and cell cycle control.
Both viral and bacterial pathogens have mechanisms designed to modulate or evade host immune responses. Molecular pathogenesis, encompassing the molecular and genetic basis of host-pathogen interactions from the perspective of both the host and the pathogen, represents a major opportunity area for virologists and bacteriologists alike. It has been suggested that the 21st century will be the "biological century," reflecting the giant leaps being made in our understanding of biological systems. It will also be the "microbiological century," as viruses and bacteria are central to that progress and remain responsible for much of humanity's suffering.