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Geographical processes and disease emergence

Geographical processes and disease emergence

Scientific concern over the global threat of emerging and re-emerging infections has escalated during the last quarter century. In addition to the raft of diseases and disease agents which were newly described from the late 1960s (including Marburg, Lassa and Ebola fevers, Legionnaires' and Lyme disease, HTLV-related leukaemias, toxic shock syndrome, AIDS and hepatitis C), recent years have seen the identification of such potentially lethal conditions as Hantavirus pulmonary syndrome, new-variant Creutzfeldt-Jacob disease (vCJD) and related encephalopathies, Brazilian haemorrhagic fever associated with Sabía virus, and epidemic cholera due to the variant Vibrio cholerae 0139. The discovery of these apparently 'new' conditions has been accompanied by an upsurge in the virulence, drug resistance, incidence and/or geographical range of such classical infections as diphtheria, influenza, malaria and tuberculosis. Two institutional responses -- the imminent publication of the strategic policy document Preventing Emerging Infectious Diseases: A Strategy for the 21st Century by the US Centers for Disease Control and Prevention (CDC)[1] and the recent establishment of the rapid-response Division of Emerging Viral and Bacterial Diseases Surveillance and Control by the World Health Organization (WHO)[2] -- are illustrative of the importance which now attaches to the problem.

These developments are the most recent in a human history that is replete with instances of the emergence and re-emergence of infectious diseases. In the first half of the present century, for example, Hans Zinsser (Rats, Lice and History, 1935; Boston: Little, Brown & Co.) provides a classic account of how typhus fever re-emerged from its 'quiet bourgeois existence' to achieve 'mediaeval ascendancy' in Revolutionary Russia. At about the same time, the pandemic of Spanish influenza (1918-19) provides a devastating example of an event associated with the cyclically re-emerging influenza A virus, whilst, in the years that followed, poliomyelitis was to reconfigure itself as one of the great epidemic diseases of the inter- and post-war periods. In earlier centuries, the appearance of smallpox associated with the mild and dispersed variola minor virus (late nineteenth century), the initial pandemic eruptions of Vibrio cholerae (early- and mid-nineteenth century), and the appearance and spread of venereal syphilis in Western Europe (sixteenth and seventeenth centuries) are further historical examples of disease emergence and re-emergence. Numerous other instances, including infamous outbreaks of mysterious diseases in antiquity, can also be cited.

This project aims to understand the processes which appear to have underpinned disease emergence and re-emergence down the ages, and to examine the operation of these factors in particular regional and temporal settings. Case studies drawn from the reports of the field officers of the United States Centers for Disease Control will be used to illustrate the principles involved. These will be supported where appropriate by examples drawn from the wider literature of emerging infections. Finally, the project will look forward, and examine the geographical factors that may have an influence on disease emergence and re-emergence in the twenty-first century. Future patterns of population movement, urbanization, demographic and ecological change are considered, and the problem of the spatial control of future epidemics through quarantine systems is assessed.

Illustrative painting

[1] For an overview of the planned document, see Centers for Disease Control and Prevention (1998). 'Preventing emerging infectious diseases: a strategy for the 21st century. Overview of the updated CDC plan.' Morbidity and Mortality Weekly Report, 47(RR-15), i-ii, 1-14.

[2] Established in 1996, the goals of EMC include: (i) the strengthening of local disease surveillance to serve as an early warning system for emergent and re-emergent diseases; (ii) the development of a network of public health laboratories to strengthen collaboration in outbreak detection and control.