Chapter 1 Infection

Immunization follows two major strategieslive

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Immunization follows two major strategies—live vaccines and inactivated vaccines. The former uses live but attenuated organisms that have been modified so they do not produce disease, but still stimulate a protective immune response. Such vaccines have been effective but carry the risk that the vaccine strain itself may cause disease. This event has been observed with the live oral polio vaccine. Although this rarely occurs, it has caused a shift back to the original Salk inactivated vaccine. This issue has reemerged with a debate over strategies for the use of smallpox immunization to protect against bioterrorism. This vaccine uses vaccinia virus, a cousin of smallpox, and its potential to produce disease on its own has been recognized since its original use by Jenner in 1798. Serious disease would be expected primarily in immunocompromised individuals (eg, from cancer chemotherapy or AIDS), who represent a significantly larger part of the population than when smallpox immunization was stopped in the 1970s. Could immunization cause more disease than it prevents? The question is difficult to answer. The safest immunization strategy is the use of organisms that have been killed or, better yet, killed and purified to contain only the immunizing component. This approach requires much better knowledge of pathogenesis and immune mechanisms. Vaccines for meningitis use only the polysaccharide capsule of the bacterium, and vaccines for diphtheria and tetanus use only a formalin-inactivated protein toxin. Pertussis (whooping cough) immunization has undergone a transition in this regard. The original killed whole-cell vaccine was effective but caused a significant incidence of side effects. A purified vaccine containing pertussis toxin and a few surface components has reduced side effects while retaining efficacy. The newest approaches for vaccines require neither live organisms nor killed, purified ones. As the entire genomes of more and more pathogens are being reported, an entirely genetic strategy is emerging. Armed with knowledge of molecular pathogenesis and immunity and the tools of genomics and proteomics, scientists can now synthesize an immunogenic protein without ever growing the organism itself. Such an idea would have astonished even the great microbiologists of the last two centuries. Summary Infectious diseases remain as important and fascinating as ever. Where else do we find the emergence of
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new diseases, together with improved understanding of the old ones? At a time when the revolution in molecular biology and genetics has brought us to the threshold of new and novel means of infection control, the perpetrators of bioterrorism threaten us with diseases we have already conquered. Meeting this challenge requires a secure knowledge of the pathogenic organisms and how they produce disease, as well as an understanding of the clinical aspects of these diseases. In the collective judgment of the authors, this book presents the principles and facts required for students of medicine to understand the most important infectious diseases.
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Immunization follows two major strategieslive vaccines and...

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