As many as 2 billion people--40 percent of the world's population--live in areas of the world where malaria is endemic. The disease, which is mainly rural, is found between the tropics of Capricorn and Cancer. Although malaria is a major health problem in Asia, Latin America, the Middle East, and the Pacific, Africa faces the brunt of the disease.
Each year, 300 to 500 million people develop malaria and 1.5 to 2.7 million die--a rate of 200 to 300 deaths worldwide each hour. Ninety percent of this mortality is in Africa, among children under age five. Pregnant women also are severely affected, as are their fetuses and infants. The health and economic burdens of malaria are wide?reaching:
Economic Development. Malaria creates a huge economic burden, because of hospital admissions, national malaria control programs and protection from mosquitoes, the cost to individuals of antimalarial drugs, treatment, and lost wages, and other expenses. Many malaria sufferers cannot afford or have no access to medical treatment. Children lose time from school and suffer throughout life from effects on cognitive development and education levels attained. Malaria also impedes economic development by limiting foreign investment, tourism, transport systems, internal movement of labor, and commerce. Attracting educated people to malarious regions is difficult, limiting the viability of areas with development potential and rich natural resources, such as the frontiers of the Amazon and the mines of South America and Africa. Because malaria strikes during the rainy harvest season, when worker productivity needs to be at its highest, the disease can harm food security and agricultural production.
Work by Sachs and Gallup at the Center for International Development at Harvard University suggests that malaria causes poverty, and is not just a result of it. Controlling for tropical location, colonial history, and geographical isolation, they found that regions that eradicated malaria had substantially higher economic growth rates than neighboring regions. Malaria affects the demography of a region by increasing infant and child mortality, thus preventing a large proportion of the population from reaching working age. Increased child mortality also leads to increased fertility as women have more children to compensate for those lost to malaria.
Pregnant Women's Health. Adults living in malaria?endemic regions develop immunity to its symptoms. Pregnancy reduces a woman's immunity, however, and ensuing malaria may result in severe anemia. Anemia prevalence in pregnant African women is high. In Malawi, 70 percent of pregnant women in one study were anemic. The main factors causing anemia in this setting are deficiencies of iron and, possibly, folate induced by inadequate diet and malarial and hookworm infections. Severe malarial anemia resulting in hemorrhage is a major cause of death among pregnant women.
Infant Birth Weight, Growth, and Development. Low maternal hemoglobin strongly predicts preterm delivery and low birth weight. Infants with low birth weight are signifi? cantly more susceptible to other infections and have a higher risk of dying during infancy. Those who survive are at greater risk for poor growth and development.
Anemia is another major cause of child morbidity and mortality in Africa. Severe anemia is the most common complication of malaria in children ages 6 months to 2 years living in malaria?endemic regions of Africa.
Malaria infection affects weight gain and stunts growth. In three malaria intervention trials in Africa that measured the protective effect of insecticide?impregnated bed nets (ITBNs), malaria mortality decreased along with all causes of child mortality. Weight gain was significantly higher among infants who slept under ITBNs. Other studies show that African children who regularly receive antimalarial prophylaxis improve weight gain.
Nutritional status strongly influences the disease burden of malaria; however, this relationship remains unclear and controversial. Many individuals at risk of malaria have micronutrient deficiencies that may hamper protective immunity. Nutrition appears to influence susceptibility to malaria and affects the course of the infection. Vitamin A is important for normal immune function, and supplementation lowers morbidity of some infectious diseases, including malaria. Vitamin A concentration in human serum negatively correlates with malaria parasite density, and Vitamin A inhibits parasite growth in laboratory experiments.
Malaria is on the rise due to insecticide resistance, antimalarial drug resistance, and environmental changes. In spite of the resistance the parasite has developed to the cheap and commonly used antimalarial drug chloroquine, ministries of health are slow to change policy to use the second?line drug Fansidar. Resistance to Fansidar is also developing due to improper use of antimalarial drugs.
The number of malaria epidemics is growing too, because of heavier rain patterns in highlands and the new breeding grounds for mosquitoes created by dams and irrigation projects. Refugees of war and natural disasters are particularly vulner?able to malaria: During civil unrest, non?immune people often move into malarious areas, and health services and malaria control programs break down. The potential ban of DDT could have severe consequences for controlling malaria in countries where this is the only affordable and effective insecticide.
Prevention and treatment of malaria and anemia during pregnancy and in children under age five should be a high priority for ministry of health policymakers, development agencies, and agencies that fund research. A number of protective policies could be implemented:
- Vitamin A and zinc supplements for infants and pregnant women protect against the severity of malaria.
- Intermittent presumptive antimalarial drug treatment for all women during pregnancy reduces placental infection, ma?ternal anemia, and the number of low birth weight babies.
- Changing the first?line antimalarial drug to a nonresistant drug and treating the disease with combinations of drugs will preserve the life of the few available antimalarial drugs.
- Insecticide spraying of households and use of ITBNs protect against malaria mortality.
The human immunodeficiency virus (HIV) epidemic further complicates Africa's malaria situation. By impairing the ability of pregnant women to limit malaria?parasite density, HIV increases the risk of premature delivery, low birth weight, and maternal death. Also, unless blood can be screened for HIV, transfusions for infants and pregnant women with life?threatening anemia will be risky. HIV sero?prevalence is commonly greater than 20 percent in antenatal clinic attendees in Africa.
The World Health Organization has launched Roll Back Malaria, an initiative aimed at reducing malaria mortality by 50 percent by 2010. This initiative aims to prevent malaria by using ITBNs and by spraying home interiors, along with improving access to health?care services.
Research is required to develop new and sustainable ways to control malaria. Strengthening the research capacity of scientists in their own countries should be a major focus for controlling malaria in Africa. The Multilateral Initiative on Malaria, an alliance of organizations and individuals, is working toward this goal, facilitating global collaboration, coordination, and capacity?building.
Even if researchers develop a vaccine within the next 10 years, the best chances for malaria control will require a many?sided attack drawing on a variety of prevention and control methods.
For further reading see J. L. Gallup and J. D. Sachs, "The Economic Burden of Malaria," unpublished manuscript (Center for Inter?national Development at Harvard University, Cambridge, Mass., USA, 1998, http://www.hiid.harvard.edu/pub/other/mal_wb.pdf); K. Marsh and R.W. Snow, "Malaria Transmission and Morbidity," Parassitologia 41 (1999): 241B246; A.H. Shankar, ANutritional Modulation of Malaria Morbidity and Mortality, Journal of Infectious Diseases 182 (supplement 1, 2000): S37B53; and the December 1999 supplement of the Annals of Tropical Medical Parasitology for the latest reviews of malaria's effect on pregnancy, the fetus, and the infant. In early 2001 a supplement to the American Journal of Tropical Medicine and Hygiene will be published entitled "The Intolerable Burden of Malaria: A New Look at the Numbers."
Andrea Egan (egana@mail.nih.gov) is the coordinator of the Multilateral Initiative on Malaria, Fogarty International Center, National Institutes of Health, Bethesda, Maryland, U.S.A.