Two things seem certain about humans wherever they have lived: they have been reproductively successful; and they have been plagued by diseases and other ill health, which, until recently, has kept their numbers in check. As humans became a numerically successful species they began to expand: first, nearby, and later, into more distant environments away from their natal territories. In so doing they met new disease vectors in the new environments and they also brought many of their ‘native diseases’ with them. As we examine the role of migration as a factor in the dissemination of disease, there is no claim to all inclusiveness; we go no further back in history than to the thirteenth century. Most of the emphasis in this chapter will be on the role of migration in the spread and acquisition of disease during the nineteenth and twentieth centuries. The instances cited are examples of the influences migration has had on disease and do not necessarily affect more people than other diseases not discussed.

Migration as a source for disease transmission

People move from place to place for many reasons. Today there are relatively few traditional nomadic populations, but temporary migrant labour still forms a large portion of the transitory agricultural work force in many parts of the world. Other, more permanent, labour migration, both intranational and international, has been an important source for new workers.