Anthony J McMichael and Rosalie E Woodruff

In recent decades there has been a well-recognized and widespread upturn in the rate of emergence, incidence, and spread of infectious diseases in all regions of the world. Many long-established infectious diseases have increased their geographic range and incidence. Antimicrobial resistance is becoming more prevalent. Of particular significance, over the past three decades there has been a succession of apparently new (mostly viral) infectious diseases. These include HIV/AIDS, Ebola virus, legionellosis, hepatitis C, hantavirus pulmonary syndrome, Nipah virus, Severe Acute Respiratory Syndrome (SARS), and, most recently, H5N1 avian influenza.

This changing tempo and pattern of infectious disease is, via diverse pathways, a consequence of the increases in intensity and scale of the human enterprise. The main influences arising from this unprecedented profile of changes in human demography, ecology and environmental impact are summarized in Box 14.1. They include increased physical mobility, extended trading, other forms of inter-population contact, changes in social relations (including changes in sexual networks and drug practices), newer commercial technologies and the scale of agriculture, intensified land clearance, biodiversity losses and other environmental disturbances, and global climate change (Weiss and McMichael, 2004).

Of particular background relevance to this chapter are the various large-scale environmental changes that human societies are now causing. Frequently these entail changes to complex natural systems and processes, which then exert influences on infectious disease patterns and risks. For example, deforestation and habitat fragmentation can facilitate the mobilization of microbes that were not previously agents of human infection, and thereby prompt the emergence of new infectious diseases in humans (see Chapter 5). Changes to ecosystems often alter the profile of species, and may thus disturb the natural constraints on vector species (e.g. mosquitoes and ticks) and intermediate host species

Swine Influenza

Swine Influenza

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