Changes in the human population and its behaviors, including intensifying means of food production and transport systems, more rapid travel and transport of people and animals across borders and continents, and changing patterns of land use have contributed to this upsurge. Other environmental changes and a host of additional factors have also contributed to conditions that favor the transmission of pathogens that develop in animal populations, then make the jump into human populations. Researchers and human and animal health advocates have focused on disease surveillance3 as a particularly critical tool for detecting, monitoring, and facilitating response to control outbreaks of zoonotic diseases in humans, but questions remain as to how to make zoonotic disease surveillance more comprehensive and timely in animal populations in order to prevent or minimize the potential for outbreaks to occur in human populations.

THE CONVERGENCE OF FORCES RESPONSIBLE FOR ZOONOSES IN HUMANS

These newly identified diseases have emerged4 primarily as a result of significant changes in human activity: population growth, changing patterns of human–animal contact, increased demand for animal protein, increased wealth and mobility, environmental changes, and human encroachment on farm land and previously undisturbed wildlife habitat. Other pathogens could follow a similar pathway.

Human factors that influence the development of pathogens include genetic and biological factors; social, political, and economic factors; human health, behavior, and attitudes; and activities such as transport and trade. Perhaps the most obvious change has been the growth in human population. At less than 3.5 billion in 1950, the world’s population reached approximately 6.5 billion in 2005 and is projected to top 11 billion by 2100 (Kern, 2008). The largest proportion of human population growth is

3

The World Health Organization defines surveillance as “the systematic ongoing collection, collation, and analysis of data for public health purposes, and the timely dissemination of public health information for assessment and public health response as necessary”; surveillance may be conducted by institutions of various kinds (WHO, 2008a).

4

For purposes of this workshop summary, a human disease is considered emerging if it meets one or more of these characteristics: has nearly appeared or is newly recognized, is more difficult to treat, has an increased incidence, is widely distributed geographically or demographically, is severe or lethal, presents new complications, has a new mode of transmission, has substantial epidemic potential, or threatens regional of global health (Breiman, 2008). The National Institute of Allergy and Infectious Diseases, however, defines emerging and re-emerging diseases as the following: “emerging diseases includes outbreaks of previously known diseases whose incidence in humans has significantly increased in the past two decades. Conversely, remerging diseases are known diseases that have reappeared after a significant decline in incidence” (NIAID, 2008).



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