of inspection and testing data generated by industry or other “third parties” to increase the breadth and depth of their surveillance.


Mary E. Wilson, M.D., F.A.C.P., F.I.S.D.A.1

Harvard University

Humans travel in numbers and at speeds unprecedented in history (IOM, 2003; Wilson and Chen, 2008). Travelers visit remote areas as well as major population centers. Humans may be displaced because of social, economic, or political upheavals or extreme events and environmental disasters (IOM, 2008). The elimination of spatial and temporal barriers, especially by long-distance air transport, means that humans can reach almost any part of the Earth today within the incubation period for most microbes that cause disease in humans. Travel is also discontinuous, often including many stops and layovers along the way. This means that travelers are part of the dynamic global process of moving biota, along with trade, which moves plants, animals, and other materials (Wilson, 1995b). Natural movement of animals via migration, and transport of seeds, microbes, and other materials via water and air currents, is the backdrop against which massive travel and trade are occurring in today’s world (Wilson, 1995a). One consequence of this movement is the juxtaposition of species that have never before had physical proximity. The contact between microbes, humans, and animals may result in infection, which may or may not be expressed in disease or death.

Another potential consequence of the movement of species, such as arthropods, mammals and other animals, and plants, whether intentional or inadvertent, is the establishment of species in new geographic areas (Tatem et al., 2006). These introductions may cause major changes in the existing ecosystem, including marine ecosystems. Many examples exist of the harmful effects of invasive species, though many species of well-regarded plants and animals in the Americas were not native to the Americas (Crosby, 1972).

Characteristics of Global Travel

Global travel has increased as reflected in Figure 2-1, showing numbers of international tourist arrivals from 1950 though 2005 and the projections until 2020. In addition to the marked increase in the overall number, there has also been a shift in areas visited by travelers, especially to areas in Asia. The 2006 figures from the World Tourism Organization showed the most rapid relative increase was to sub-Saharan Africa (UNWTO, 2008b). Travel between regions


Associate Professor of Global Health and Population, Harvard School of Public Health; Associate Clinical Professor, Harvard Medical School. E-mail: mewilson@hsph.harvard.edu.

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