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Volume 2, Number 4—October 1996

Volume 2, Number 4—October 1996   PDF Version [PDF - 1.07 MB - 124 pages]


  • Guarding Against the Most Dangerous Emerging Pathogens: Insights from Evolutionary Biology PDF Version [PDF - 98 KB - 13 pages]
    P. W. Ewald
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    Control of emerging infectious diseases will be difficult because of the large number of disease-causing organisms that are emerging or could emerge and the great diversity of geographic areas in which emergence can occur. The modern view of the evolution of pathogen virulence—specifically its focus on the tradeoff between costs and benefits to the pathogen from increased host exploitation—allows control programs to identify and focus on the most dangerous pathogens (those that can be established with high virulence in human populations).

  • Social Inequalities and Emerging Infectious Diseases PDF Version [PDF - 85 KB - 11 pages]
    P. Farmer
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    Although many who study emerging infections subscribe to social-production-of-disease theories, few have examined the contribution of social inequalities to disease emergence. Yet such inequalities have powerfully sculpted not only the distribution of infectious diseases, but also the course of disease in those affected. Outbreaks of Ebola, AIDS, and tuberculosis suggest that models of disease emergence need to be dynamic, systemic, and critical. Such models—which strive to incorporate change and complexity, and are global yet alive to local variation—are critical of facile claims of causality, particularly those that scant the pathogenic roles of social inequalities. Critical perspectives on emerging infections ask how large-scale social forces influence unequally positioned individuals in increasingly interconnected populations; a critical epistemology of emerging infectious diseases asks what features of disease emergence are obscured by dominant analytic frameworks. Research questions stemming from such a reexamination of disease emergence would demand close collaboration between basic scientists, clinicians, and the social scientists and epidemiologists who adopt such perspectives.


  • Molecular Mechanisms of Bacterial Virulence: Type III Secretion and Pathogenicity Islands PDF Version [PDF - 315 KB - 18 pages]
    J. Mecsas and E. J. Strauss
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    Recently, two novel but widespread themes have emerged in the field of bacterial virulence: type III secretion systems and pathogenicity islands. Type III secretion systems, which are found in various gram-negative organisms, are specialized for the export of virulence factors delivered directly to host cells. These factors subvert normal host cell functions in ways that seem beneficial to invading bacteria. The genes encoding several type III secretion systems reside on pathogenicity islands, which are inserted DNA segments within the chromosome that confer upon the host bacterium a variety of virulence traits, such as the ability to acquire iron and to adhere to or enter host cells. Many of these segments of DNA appear to have been acquired in a single step from a foreign source. The ability to obtain complex virulence traits in one genetic event, rather than by undergoing natural selection for many generations, provides a mechanism for sudden radical changes in bacterial-host interactions. Type III secretion systems and pathogenicity islands must have played critical roles in the evolution of known pathogens and are likely to lead to the emergence of novel infectious diseases in the future.

  • New Vaccines for the Prevention of Pneumococcal Infections PDF Version [PDF - 68 KB - 10 pages]
    H. Käyhty and J. Eskola
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    Streptococcus pneumoniae is a major cause of acute otitis media, pneumonia, bacteremia, and meningitis. Because in recent years antibiotic-resistant pneumococcal strains have been emerging throughout the world, vaccination against pneumococcal infections has become more urgent. The capsular polysaccharide vaccine that has been available is neither immunogenic nor protective in young children and other immunocompromised patients. Several pneumococcal proteins have been proposed as candidate vaccines, but no human studies associated with them have been reported. Clinical trials of first-generation pneumococcal conjugate vaccines have shown that covalent coupling of pneumococcal capsular polysaccharides to protein carriers improves the immunogenicity of the polysaccharides. The protective efficacy of the conjugate vaccines against carriage, acute otitis media, and invasive infections is being studied.

  • A Mathematical Model and CD4+ Lymphocyte Dynamics in HIV Infection PDF Version [PDF - 147 KB - 7 pages]
    T. Hraba and J. Dolezal
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    The paper presents a model of CD4+ lymphocyte dynamics in HIV-infected persons. The model incorporates a feedback mechanism regulating the production of T lymphocytes and simulates the dynamics of CD8+ lymphocytes, whose production is assumed to be closely linked to that of CD4+ cells. Because CD4+ lymphocyte counts are a good prognostic indicator of HIV infection, the model was used to simulate such therapeutic interventions as chemotherapy and active and passive immunization. The model also simulated the therapeutic administration of anti-CD8 antibodies; this intervention was assumed to activate T-cell production by activating a feedback mechanism blocked by the high numbers of CD8+ lymphocytes present in HIV-infected persons. The character and implications of the model are discussed in the context of other mathematical models used in HIV infection.

  • Chlamydiae as Pathogens: New Species and New Issues PDF Version [PDF - 92 KB - 13 pages]
    R. W. Peeling and R. C. Brunham
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    The recognition of genital chlamydial infection as an important public health problem was made first by the recognition of its role in acute clinical syndromes, as well as in serious reproductive and ocular complications, and secondly by our awareness of its prevalence when diagnostic tests became widely accessible. The recent availability of effective single dose oral antimicrobial therapy and sensitive molecular amplification tests that allow the use of noninvasive specimens for diagnosis and screening is expected to have a major impact in reducing the prevalence of disease in the next decade. Clinical manifestations associated with Chlamydia pneumoniae infection continue to emerge beyond respiratory illness. In particular, its association with atherosclerosis deserves further investigation. Chlamydia pecorum, a pathogen of ruminants, was recently recognized as a new species. The continued application of molecular techniques will likely elucidate an expanding role for chlamydiae in human and animal diseases, delineate the phylogenetic relationships among chlamydial species and within the eubacteria domain, and provide tools for detection and control of chlamydial infections.




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