Unforeseen Effects on Health
Mary E. Wilson
The desire to find regions untouched by human development leads travelers to explore increasingly remote areas and brings them in contact with relatively isolated human and animal populations. Current materials, equipment, and methods of travel allow individuals to rapidly penetrate physical and vegetation barriers that would have stopped, or markedly slowed, even intrepid explorers in the past. The time to reach remote areas is often short, and travelers may sample remote areas for a brief time, sometimes a few days or less. The process of travel typically involves multiple places and populations, and all may be affected directly or indirectly by the travel of humans.
Travelers form an important bridge to diverse geographic areas and increase the mingling of genetic material from multiple species as they also transform the landscape (Wilson 1995a). This chapter focuses on three themes: movement, mixing, and pressures as they relate to changing patterns of infectious diseases. A number of examples will illustrate the complex interactions that influence infectious diseases.
Movement involves all species, but the volume, speed, and reach of human travel today is unprecedented. Movement of other species is closely linked to human traffic as humans transport other species with them or move them for commerce. Humans also displace animals through land development and by altering habitats (Wilson 1995b). Although some animals migrate, sometimes over long distances, they typically follow paths or routes that may remain remarkably constant over many generations. Human activities, including importation of exotic animals, move animals out of traditional habitats and migration pathways.
Travel by the majority of humans tends to follow set paths, roads, and routes. Modern technology is changing the range of destinations, making it easier for