The Disease Environment

In addition, Africans had their own tropical illnesses: malaria, blackwater fever, yellow fever, trypanoso­miasis (sleeping sickness), filariases, leishmaniasis {kala-azar), schistosomiasis (bilharziasis), onchocer­ciasis (river blindness), leprosy, yaws, guinea worm, helminthiasis, relapsing fever (louse- and tickbome), and tropical ulcer.

By the mid-nineteenth century, tropical Africans were afflicted by most of the diseases of the temper­ate Old World, such as brucellosis (Malta fever), Xmdulant fever, cerebrospinal meningitis, cholera, diphtheria, influenza, measles, plague, pneumonia, poliomyelitis, smallpox, tuberculosis, typhoid fever (enteric fever), typhus and other rickettsial infec­tions, venereal diseases, and whooping cough. The causes of 50 to 90 percent of illness and death among the poor in the underdeveloped world, including Af­rica, fall into two main groups: nutritional deficien­cies and communicable diseases (Sanders 1985).

What constitutes a disease environment and what causes it to change? Every human community coex­ists with specific microorganisms that contribute to the disease environment of the group. Many diseases represent the failure of one organism, in this case human beings, to cope successfully with competing organisms, in this case microorganisms, in the cease­less struggle for survival. A disease environment con­tains many elements: humans, animals, various other forms of flora and fauna, microorganisms, cli­mate, and geographic features. Many disease envi­ronments are often located close to one another, and these undergo frequent and sometimes rapid change. For instance, after a period of interaction with a sta­ble human population, disease-causing pathogens can adapt and produce new strains in response to the immune defenses produced by that population. In recent decades this has been demonstrated in parts of the world by the appearance of new strains of chloroquinine-resistant Plasmodium falciparum, the cause of the most deadly of the malarial diseases.

Conversely, human host communities develop im­munity to endemic diseases. In other words, humans who survive the diseases of their environment often acquire some resistance to further infection. Epidem­ics of disease occasionally flare up when nonimmune members of the community are exposed to pathogens or when newcomers in large enough numbers reach a disease environment containing pathogens against which they have no immune protection.

As stated previously, disease environments are af­fected by both natural and sociocultural factors. A natural factor of much importance in Africa is the proliferation of insects, many of which serve as vec­tors of disease-causing pathogens. Another factor is climate, which can be a major determinant of those diseases that have specific requirements of tempera­ture, humidity, or aridity. An equally important fac­tor encompasses the sociocultural practices of com­munities. For instance, ritual practices may bring humans into regular and intimate contact with cer­tain features of the physical environment that re­sults in contact with disease-causing pathogens. Shrines hidden deep in forested regions may bring humans into contact with pathogen-bearing insects such as the tsetse fly and anopheles mosquito. In addition, agricultural practices, such as the cultiva­tion of certain crops close to homesteads, often bring humans into contact with pathogens. And changes in crops or techniques often provide new ecological niches in which disease-bearing pathogens flourish. An example of this is the introduction by a British colonial officer of a new variety of hedge, the Iantana, from India into Uganda in the 1940s. The Iantana flourished in its new environment, gradu­ally spreading northward toward the southern Su­dan. Unfortunately, it provided an excellent habitat for a species of tsetse fly, Glossina pallidipes, which in turn introduced new strains of trypanosomes, the cause of human sleeping sickness.

Perhaps the most important factors in disease envi­ronments are water supply and human excreta. Wa­terborne diseases include typhoid fever, poliomyeli­tis, infectious hepatitis, cholera, schistosomiasis, dracunculiasis, and leishmaniasis. Water supplies and sewage disposal are complex subjects of much concern to health planners in the late twentieth century.

Rather, clean water supplies and sanitary sewage disposal, as means of disease prevention, were, until very recently, solely the concern of the engineer. Thus, a major source of much human disease was neglected by medical people. The colonial legacy in­cluded very little in the way of safe/water supplies and effective sewage disposal systems, except in a few of the urban areas where the Europeans them­selves resided. And Africans are suffering the effects to the present day.

Last but hardly least among the African “patho­genic factors” is protein-energy malnutrition, for the excessive mortality of African children under 5 years of age is due largely to the synergism between protein-energy malnutrition and infectious and parasitic diseases. Until fairly recently, nutrition has been largely ignored in relation to morbidity, yet it is a vitally important key to understanding the widespread perception of Africa as a “disease- ridden” continent.

Earlier theories of epidemiology held that expo­sure to new pathogens was sufficient cause for epi­demic outbreaks, and much emphasis was laid on the increased interactions of African populations, witnessed by Europeans from the mid-nineteenth century on, as an explanation for apparently in­creased rates of morbidity and mortality. More re­cently, however, it has been argued that more than mere exposure is needed to explain why humans fall ill and why epidemics flare. Thomas McKeown (1979) argued convincingly that, for almost the whole of human existence, disease and early death have resulted from basic deficiencies or from haz­ards related to them and that the role of nutrition is of paramount importance.

Thus, medical services, specific remedies, and the increasingly complex technology Ofbiomedicine may not provide the best solutions to African health prob­lems; rather, the total ecology of health and disease may be a more fruitful area of study for future health planners.

Maryinez Lyons The author thanks Ian Timaeus for his help.