Changing Epidemiology of Malaria in Africa: Substantial Gains in Many Areas
By Brian G. Blackburn, MD, and Michele Barry, MD, FACP
Dr. Blackburn is a Clinical Assistant Professor in the Division of Infectious Diseases and Geographic Medicine at Stanford University School of Medicine. Dr. Barry is the Senior Associate Dean of Global Health at Stanford University School of Medicine.
Dr. Blackburn reports no financial relationships related to this field of study. Dr. Barry serves as a consultant for the Ford Foundation, and her program receives funding from Johnson & Johnson Corporate Foundation.
Synopsis: Malaria control initiatives have resulted in substantial declines in the disease burden in many regions of Africa. The Horn of Africa, southern, and eastern Africa have noted declines in many malaria indices over the past decade. Data are mixed in west Africa, and less success has been reported in central Africa, although this is probably in part due to publication bias and political instability in the region. Continued expansion of malaria control initiatives is needed.
Source: O'Meara WP, Mangeni JN, Steketee R, et al. Changes in the burden of malaria in sub-Saharan Africa. Lancet Infect Dis. 2010;10:545-555.
The past decade has seen malaria control return to the forefront of global public health agendas. After years of relative neglect, multiple international initiatives, such as Roll Back Malaria, the Global Fund, and the President's Malaria Initiative, have resulted in funding for malaria control on a scale not seen in decades. As a result, greater coverage has been possible for several malaria control measures, such as insecticide-treated bednets (ITNs), the use of artemisinin-based combination therapies (ACTs), and indoor residual spraying. This review focused on the impact of these measures in Africa on a regional basis over the past decade, through a review of published reports.
Reports regarding malaria burden in the Horn of Africa have been almost universally encouraging. In Ethiopia, a 70% reduction in outpatients with malaria and in children under 5 (U5s) admitted for malaria was seen from 2000 to 2007, and similar results were noted in Eritrea. In east Africa, data are also encouraging. Coastal Kenya has seen 75% reductions in pediatric malaria admissions between 2003 and 2007, and decreases in malaria prevalence from 35% to 1% in one district since the mid 1990s. In western Kenya, a 42% reduction in all-cause mortality among U5s was seen between 2003 and 2007, with a 16% decline in malaria-specific mortality. In Rwanda, malaria cases declined more than 50% between 2005 and 2007. In contrast, western Uganda noted increasing numbers of malaria cases and deaths in district hospitals from 1991 to 2000. Although northeastern Tanzania saw the number of malaria cases increase between 1994 and 2002, prevalence rates have since fallen dramatically.
Data are sparse from central Africa because of both poor infrastructure and a relative lack of research initiatives. In Brazzaville, Congo, the percentage of pediatric admissions due to malaria (30%) did not change between 1989 and 2001. In eastern Sudan, a slight decline was seen in the proportion of positive malaria smears between 1998 and 2002. Two small studies in Cameroon in 2000 and 2004 showed a slight decline in malaria prevalence among asymptomatic children, but no change among febrile children.
In South Africa, sustained malaria control over decades has stopped transmission throughout most of the country except the northeastern border regions adjacent to Mozambique and Swaziland, which include game parks. Although drug resistance, increasing HIV prevalence, and mosquitoes resistant to pyrethroid insecticides contributed to a five-fold increase in malaria cases in Kwa-Zulu Natal province between the mid-1990s and 2001, an 85% decline in malaria admissions, deaths, and outpatient malaria cases was seen subsequently; by 2003, cases had declined by 99% from their peak in 2000. In Zambia, between 2006 and 2008 pediatric malaria prevalence declined by 53% and anemia declined by 69%. In Zimbabwe, data are less encouraging, where increasing morbidity and mortality from suspected malaria was reported between 2001 and 2003.
In west Africa, reports are mixed. Gambian surveillance data demonstrated a 50-85% decline in the prevalence of outpatient malaria and a 25-90% decline in malaria admissions. In Libreville, Gabon, 80% fewer children with positive blood smears were reported at one hospital between 2003 and 2008. In Senegal, one village showed an increase in malaria incidence between 1998 and 2001 (followed by a decline of 20%), while in Niakhar, Senegal, presumptive malaria cases and mortality fluctuated considerably between 1992 and 2004. A Nigerian hospital reported an increasing proportion of hospital admissions due to severe malaria between 2000 and 2005. In Burkina Faso, a three-fold increase in malaria cases at health facilities between 2000 and 2007 was seen.
Commentary
During the past 3-5 years, the burden of malaria has declined substantially in several areas of sub-Saharan Africa. Recent successes in Ethiopia, Eritrea, Kenya, Rwanda, and Zambia, combined with ongoing control in South Africa have resulted in impressive gains on the continent most plagued by this disease. However, other locations have seen a static or deteriorating picture, such as in Uganda, Zimbabwe, and several countries in central and west Africa; in addition, the situation in large parts of Africa is simply unknown.
Although some progress has resulted from long-standing malaria control programs (such as in South Africa), many other countries have experienced their gains coincident with the recent scaling up of malaria control initiatives. In many such areas, the temporal association of the changing epidemiology of malaria with the introduction of specific interventions is compelling. Indoor residual spraying, increased ITN coverage, and improved case management (such as with the introduction of ACTs to an area with drug resistance) reduce morbidity and mortality from malaria. Indoor residual spraying, for example, was integral to the achievement of successful malaria control in South Africa, but has had less effect elsewhere. The evidence that ITNs can provide substantial protection against morbidity and mortality from malaria is even stronger, especially when used by a high proportion of the population.1,2 Encouragingly, global production of ITNs more than tripled from 2004 to 2008, use of ITNs by U5s increased by three- to 10-fold between 2000 and 2008 in many African countries, and long-lasting ITNs are now becoming integral parts of many distribution campaigns. In Zambia, household ITN ownership increased from 22% in 2004, to 62% in 2008; in Eritrea, ITNs were owned by 80% of households by 2004. Lastly, widespread deployment of ACTs, which are partly gametocytocidal, can also impact malaria transmission in communities where a high proportion of symptomatic infected individuals seek treatment. An increase of about 25-fold in the global procurement of ACTs has occurred during the past five years.
Expanding and maintaining sustainable malaria control programs is an essential goal, based on the results described above. A promising way forward may be through the integration of disease control campaigns. Combining ITN distribution with filarial mass drug administration campaigns or with mass childhood vaccination campaigns has been shown to save resources while increasing the coverage of both measures.3 However, we await the holy grail of an effective malaria vaccine to finally be able to consider malaria eradication rather than control. Late-stage clinical testing (Phase 3 trial) of the GlaxoSmithKline circumsporozoite antigen (RTS,S) vaccine is under way at 11 sites in seven African countries (Gabon, Mozambique, Tanzania, Ghana, Kenya, Malawi, and Burkina Faso). Sanaria is a biotechnology firm with a whole-organism approach for a vaccine that has recently undergone an initial safety and test-of-concept trial with this approach. Live attenuated parasites in the form of sporozoites are harvested from irradiated mosquitoes and combined with adjuvant to form a vaccine. The confluence of increased funding, international interest, and a future vaccine may finally begin to stem the tide of this disease on the continent most affected by it.
References
- Phillips-Howard PA, Nahlen BL, Kolczak MS, et al. Efficacy of permethrin-treated bed nets in the prevention of mortality in young children in an area of high perennial malaria transmission in western Kenya. Am J Trop Med Hyg 2003;68 (Suppl 4):23–29.
- ter Kuile FO, Terlouw DJ, Kariuki SK, et al. Impact of permethrin-treated bed nets on malaria, anemia, and growth in infants in an area of intense perennial malaria transmission in western Kenya. Am J Trop Med Hyg 2003;68 (Suppl 4):68–77.
- Blackburn BG, Eigege A, Gotau H, et. al. Successful integration of insecticide-treated bednet distribution with mass drug administration in Central Nigeria. Am J Trop Med Hyg 2006;75;650-655.
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