It is also essential in discovering the emergence of

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It is also essential in discovering the emergence of "new" diseases, whether they are truly new (AIDS) or just recently discovered (Legionnaires disease). Solving mysterious outbreaks or recognizing new epidemiologic patterns have usually pointed the way to the isolation of new agents.
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Epidemic spread and disease are facilitated by malnutrition, poor socioeconomic conditions, natural disasters, and hygienic inadequacy. In previous centuries, epidemics, sometimes caused by the introduction of new organisms of unusual virulence, often resulted in high morbidity and mortality rates. The possibility of recurrence of old pandemic infections remains, and, as with AIDS, we are currently witnessing a new and extended pandemic infection. Modern times and technology have introduced new wrinkles to epidemiologic spread. Intercontinental air travel has allowed diseases to leap continents even when they have very short incubation periods (cholera). The efficiency of the food industry has sometimes backfired when the distributed products are contaminated with infectious agents. The well- publicized outbreaks of hamburger-associated Escherichia coli O157:H7 infection constitute an example. The nature of massive meat-packing facilities allowed organisms from infected cattle on isolated farms to be mixed with other meat and distributed rapidly and widely. By the time outbreaks were recognized, cases of disease were widespread, and tons of meat had to be recalled. In simpler times, local outbreaks from the same source would have been detected and contained more quickly. Of course, the most ominous and uncertain epidemiologic threat of these times is not amplification of natural transmission but the specter of unnatural, deliberate spread. Anthrax is a disease uncommonly transmitted by direct contact of animals or animal products with humans. Under natural conditions, it produces a nasty but usually not life-threatening ulcer. The inhalation of human-produced aerosols of anthrax spores could produce a lethal pneumonia on a massive scale. Smallpox is the only disease officially eradicated from the world. It took place so long ago that most of the population has never been exposed or immunized and are thus vulnerable to its reintroduction. We do not know whether infectious bioterrorism will work on the scale contemplated by its perpetrators, but in the case of anthrax we do know that sophisticated systems have been designed to attempt it. We hope never to learn whether bioterrorism will work on a large scale. Pathogenesis Once a potential pathogen reaches its host, features of the organism determine whether or not disease ensues. The primary reason why pathogens are so few in relation to the microbial world is that being a successful pathogen is very complicated. Multiple features, called virulence factors, are required to persist, cause disease, and escape to repeat the cycle. The variations are many, but the mechanisms used by many pathogens are now being dissected at the molecular level.
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