JOHN C. CALDWELL, JOHN K. ANARFI, and PAT CALDWELL
Migration has always facilitated the spread of any infectious disease. This has been the case even with diseases transmitted by insect vectors as has been demonstrated in Nigeria ( Prothero, 1965). Migration does this in two ways. First, it brings more people into contact with each other and is the means whereby diseases can be carried from one community to others over considerable distances. Second, it has been a major factor in the growth of urban areas where dense populations in close contact provide a context for epidemics. Sexually transmitted diseases are associated in yet other ways with migration, because many migrants move away from their usual sexual partners and seek new sexual outlets. Populations along the ancient trading routes of Africa and Asia have long experienced higher levels of venereal disease than more isolated settlements ( David and Voas, 1981). In regard to both sexual and other behaviour, migration takes individuals away from their home places where their doings are often monitored and controlled, to distant parts where no one feels individual responsibility for exerting much influence over them.
All these tendencies have long been on the increase. The Black Death spread in a few years from China to Western Europe in a way that would have been impossible among pre-Neolithic populations. The influenza epidemic in the second decade of this century broke out almost simultaneously in widely scattered parts of the world. This has also been the case with the AIDS epidemic, and the low levels of the disease in some parts of the world can no longer be explained by their distance from an epicentre.
The European expansion brought with it infectious diseases which decimated the native population of the Americas and severely affected parts of Africa, Asia, and the Pacific. This phenomenon arose not merely from contact with new pathogens but also from a disruption of society that catalysed the spread of disease. It is almost certainly wrong to imply, as Frank ( 1992: 90-1) appears to do, that Africa was free of the major sexually transmitted diseases until the European forward____________________