Disease Patterns from AD 1000 to 1500

By about A.D. 1000, most of the better agricultural lands had been settled by village farmers. There was still a frontier in the extreme south, and pastoral groups were important in and near the deserts and in parts of the East African interior, but the pygmy and Khoisan peoples were increasingly being pushed into pockets of marginal jungle or desert - a process that has continued until the present. Farming was often of a slash-and-burn type, with villages moving to seek new lands at intervals of several years to a generation or more, but hundreds of people often lived close together in compact, relatively permanent settlements. Small cities began to develop in response to long-distance trade in parts of the western Sudan and along the east coast.

These long, complex processes must have had important implications for health conditions. Hunting-gathering populations were too sparse to support many acute diseases, especially smallpox, measles, poliomyelitis, chickenpox, and other viral infections that produce long-lasting immunities. They were mobile enough to avoid living for long in close proximity to accumulations of their own wastes.

Village life, on the other hand, whether based on fishing and intensive collecting or on agriculture, put much larger numbers of people in close, continuous contact in fixed places. Diseases of crowds, like many of those caused by respiratory transmission of common bacterial and viral infections, could be readily transmitted. Disposal of wastes and contamination of water became problems, and failure to solve them resulted in much greater opportunities for the spread of gastrointestinal infections, such as dysentery and diarrhea of various etiologies, as well as Ascaris, Trichuris, and other parasitic worms. Hookworm, transmitted by fecal contamination of soil, was also common in many places. Villages and land cleared for agriculture helped provide breeding sites for the mosquito vectors of malaria, yellow fever, and filariasis. Animal husbandry also provided enhanced opportunities for transmission of beef and pork tapeworms, anthrax, and other diseases. Animal manure attracted disease-carrying flies. In Africa, as elsewhere, the price for the advantages of village life and a more reliable and abundant food supply was a dramatic increase in the variety and frequency of infectious diseases.

Africans gradually developed immunologic and cultural defenses against many of these diseases, and population grew, although much more slowly than in recent decades. Although direct evidence is lacking, it is likely that the pool of diseases afflicting sedentary populations was especially deadly for indigenous hunting-gathering groups beyond the expanding agricultural frontier. As in the Americas, Australia, New Zealand, and probably also Siberia, diseases from what William McNeill has called "civilized disease pools" helped to pave the way for newcomers by killing large numbers of the aboriginal populations.

By about A.D. 1000 the more densely inhabited portions of Africa, or at least those north of the equatorial forest, probably had had at least limited experience with most of the infectious diseases common to the Eurasian land mass. There was some attenuation, however, due to distance and relative isolation, as well as modifications from the tropical environment and the fairly low average population density. The disease mixture would be enriched and the frequency of outbreaks increased in later centuries as a result of more intensive commercial and other contacts with the Moslem world and with western Europe.

We have little direct knowledge of health conditions before about 1500, but scattered data and inferences from more recent times allow some general, if somewhat speculative, comments. Many Africans suffered from a wide range of intestinal parasites spread by the fecal-oral route, and from dysentery and other bacterial and viral diseases associated with poor sanitation, although cholera did not exist here until it was imported from Asia in the nineteenth century.

Some have argued that there is an old focus of plague in central Africa, but the evidence for this is not compelling, and it is not clear that plague had any real importance in Africa before the late nineteenth century. Smallpox was known in Egypt by the sixteenth century B.C., and may have been epidemic in Ethiopia as early as 570. South of the Sahara, smallpox and perhaps also measles were probably uncommon and tended to occur in epidemic form at long intervals. Respiratory infections like pneumonia were uncommon, and tuberculosis was rare or absent, except perhaps in trading towns. Cerebrospinal meningitis probably did not appear until the late nineteenth century. Guinea worm and schistosomiasis were, then as now, focal waterborne infections with high prevalence rates in some localities.

Except in the deserts, malaria was ubiquitous. It tended to spread in the forest as land clearance for farming created better breeding sites for Anopheles mosquito vectors. The antiquity of falciparum malaria is indicated by the widespread prevalence of sickle cell trait, a costly but effective genetic defense. Most African groups lack Duffy antigen, probably another old genetic adaptation, which protects them against vivax malaria. Yellow fever existed in forest areas, but attacked mainly children and may have caused relatively little harm. Yaws and leprosy were especially prevalent in moister climates. Trachoma was more common in arid regions. Gonorrhea probably had been established by the first century A.D., at least in the towns of the western Sudan, but syphilis was a post-Columbian im port via Europe and North Africa. Human and animal trypanosomiasis occurred in places where tsetse flies lived. Then, as now, animal trypanosomiasis prevented stock raising in forest areas. Pockets of savanna bush were infested with flies carrying both human and animal pathogens; these places were generally known and avoided.

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