Background: Malaria in Sub-Saharan Africa
Malaria in sub-Saharan Africa is a problem of dimensions unlike those seen anywhere else in the world today. Malaria, which can be fatal, is transmitted to humans by mosquito vectors of the Anopheles species. The magnitude of malaria in Africa is affected by a variety of factors, none of which addressed alone is likely to effect a resolution. It is further compounded by the generally poor social and economic conditions in sub-Saharan Africa. Approximately 80 percent of malaria cases and 90 to 95 percent of malaria-related deaths in the world are estimated to be in Africa. In some areas of sub-Saharan Africa people receive 200 to 300 infective bites per year (Beier, Perkins, and Onyango, 1990; Molineaux and Gramicia, 1980). At least 300 to 500 million malaria episodes are treated annually in sub-Saharan Africa. Moreover, many communities engage in preventive and treatment practices outside what is provided by "official programs" (Mwabu, 1991; Deming, Gayibor, Murphy, Jones, and Karsa, 1989). The disease afflicts pregnant women, young children, and migratory populations particularly severely because of their low or non-existent immunity to the disease: Each year between 675,000 and 1,000,000 deaths among children in sub-Saharan Africa are attributed to malaria.
Problems of Control in Africa
The vector population in sub-Saharan Africa is uniquely effective, with the six species of the Anopheles gambiae complex being the most efficient vectors of human malaria in the region, and often considered the most important in the world. An. funestes is also capable of producing very high inoculation rates in a wide range of geographic, seasonal, and ecological conditions (Coluzzi, 1984). These vectors have proven effective in transmitting the malaria parasite to humans across the region, in rural and urban areas alike. An. pharoensis is also widely distributed in Africa, geographically and ecologically, and can maintain active transmission of malaria even in the absence of the main malaria vectors (Janssens and Wery, 1987, p. 489). Moreover, these vectors have shown resistance to numerous insecticides, including DDT, various organo-phosphates, and some carbamates. Finally, there is a considerable lack of information regarding vector habits, such as where Anopheles rest during the day, information that is critical for control efforts.
Another contributing factor in sub-Saharan Africa is the diversity of the parasite that infects humans. Although Plasmodium falciparum accounts for the most severe cases of malaria and "for over 90 percent of infections in most areas of tropical Africa where malaria is endemic," (Beausoleil, 1986) it is by no means the sole perpetrator. P. vivax, malariae, and ovale contribute significantly to the pool in sub-Saharan Africa. Resistance of P. falciparum to chloroquine is on the increase across the continent, having first been reported in East Africa in the 1970s. This resistance has since spread rapidly; for example, in Kenya chloroquine-resistant P. falciparum was first discovered in an infant in 1982. Since then the reported level of chloroquine-resistant P. falciparum has reached 20 percent in west Kenya and 50 percent on the coast. There have also been reports of increasing multiple-drug resistance to drugs other than chloroquine, such as amodiaquine, mefloquine, and Fansidar, rendering treatment of malaria even more problematic.
Human and financial resources devoted to malaria control are grossly inadequate. Most African countries have faced declining GNP/GDP, and often this has resulted in a decrease in health and other social services. Since the "malaria eradication" era of the 1950s and 1960s, there has been a paucity of trained malaria researchers and control program managers. Inabilities to acquire up-to-date information and equipment, as well as inadequate salaries, have caused many able and promising scientists and technicians to be trained and employed outside of Africa.
Moreover, significant cultural, social, and environmental variations among communities require that strategy design include an evaluation of the characteristics of the largest communities. Community leaders need to be identified and consulted. Control programs must be structured to conform to a community's expectations and priorities. Concerns such as sleeping, working, and recreational hours and locations; religious practices; proximity of homes to breeding areas; understanding of disease etiology; and acceptance and use of various prevention and control measures (e.g., coils, sprays, chemoprophylaxis, etc.) have an impact on malaria transmission, and hence must be considered when devising control and health education strategies. Level of economic development has also been shown to affect malaria prevalence rates and propensity to use control measures: "...during the initial stages of economic development, increases in income and high rates of malaria prevalence are likely to coexist. However, at a certain threshold level of income, there occurs a reversal in the positive relationship between incomes and malaria prevalence..." (Mwabu).
The severity of malaria and its relationship to other diseases have heightened the urgency of controlling the problem in African countries. Cerebral malaria is now estimated to be responsible for a fatality rate of more than 20 percent of malaria cases, even in urban areas (Warrell, Molyneux, and Beales, 1990). Mortality and morbidity rates due to malaria, as monitored in specific countries, appear to be increasing. For example, reported deaths due to malaria increased from 2.1 percent of cases in 1984 to 4.8 percent in 1986, to 5.8 percent in 1988 in Zaire. Malaria deaths as a percent of mortality in Zaire increased from 29.5 percent in 1983, to 45.6 percent in 1985, and to 56.4 percent of all mortality in 1986 (Paluku, presentatioon at AAAS workshop, May 1991). Pediatric anemia, in 1987, had increased to three times its 1984 prevalence among malaria patients (Greenberg, Nguyen-Dinh, and Mann, 1988). Moreover, in some cases HIV infection from blood transfusions is becoming a major concern.
Population, political, and economic pressures have been forcing groups to leave non-endemic areas throughout the region (e.g., in Ethiopia, Somalia, and the Sudan) and to enter endemic areas without natural immunity. Long-term migrants, as well as seasonal laborers and nomadic populations, suffer some of the gravest consequences because of their transient status. Also, recent urbanization trends in Africa have caused increases in both the human and vector pools. These population movements as well as various climatic factors have introduced malaria into areas that had previously been malaria-free. This trend has been observed in major cities, which in recent years have lost their malaria-free status, as well as in areas of higher altitude, for example in parts of Zaire (Paluku, personal communication, November 1990), Madagascar, and Kenya, among others. Urbanization also decreases the salt marshes and rain forests that have traditionally been ecologically unfriendly to An. gambiae. Moreover, new urban construction is usually accompanied by pools of water that serve as effective breeding sites, particularly for An. gambiae, and compounds the problems of generally deteriorating urban environments.
Agricultural development projects have also very seriously affected transmission; through deforestation, desalinization, and irrigation, the environment has been altered drastically. Furthermore, development projects in hydroelectricity, mining, industry, and agriculture have created ecological changes, increasing mosquito contact with humans, many of whom had no prior exposure to malarious mosquitoes, and hence no natural immunity. In Rwanda, for example, populations accustomed to inhabiting higher altitudes have been forced, because of intense population density and growth reaching 3.7 percent annually, to move into the swampy areas more favorable to anopheline breeding. However, limited success has been reported as a few development projects have begun to incorporate disease prevention and sanitation measures in the planning and implementation phases. For example, the Société pour l'Expansion et la Modernization de la Riziculture de Yagua (SEMRY) in Mayo-Danai, Cameroon, managed to fill a 35,000 ha lake, build irrigation canals, and resettle migrant populations for a rice development project without increasing the incidence of malaria or schistosomiasis in the project area. Their success was attributed to the controls implemented, including: regular drain and canal cleaning, provision of drinking water in villages (tube wells or bore-holes with hand pumps), and careful design of canals so they would not be conducive to mosquito breeding (Audibert, Josserane, Josse, and Adjidji, 1990). (Several other examples may be found among the case studies in the Appendix [note: of the print version].)
This combination of devastating factors and influences has resulted in an inability to control malaria across this vast continent. Yet, as this report will demonstrate, with renewed attention, resources, and strategies targeted to discrete environments, there is hope for success in malaria control in sub-Saharan Africa.