Malaria is by far the world's most important tropical parasitic disease, and it kills more people than any other communicable disease, except tuberculosis. In many developing countries, and in Africa especially, malaria exacts an enormous toll in lives, in medical costs, and in days of labor lost.
The geographical area affected by malaria has shrunk considerably over the past 50 years, but control is becoming more difficult and gains are being eroded. Increased risk of the disease is linked with changes in land use, to activities like road building, mining, logging, and agricultural and irrigation projects, particularly in "frontier" areas like the Amazon and Southeast Asia. Other causes of its spread include global climatic change, disintegration of health services, armed conflicts and mass movements of refugees. The emergence of multi-drug resistant strains of parasites is also exacerbating the situation. Via the explosion of easy international travel, imported cases of malaria are now more frequently registered in developed countries. Malaria is re-emerging in areas where it was previously under control or eradicated e.g. in the Central Asian Republics of Tajikistan and Azerbaijan, and in Korea.
Malaria is a public health problem today in more than 90 countries, inhabited by a total of some 2,400 million people - 40% of the world's population. Worldwide prevalence of the disease is estimated to be in the order of 300-500 million clinical cases each year. More than 90% of all malaria cases are in sub-Saharan Africa. Mortality due to malaria is estimated to be 1.5 to 2.7 million deaths each year. The vast majority of deaths occur among young children in Africa, especially in remote rural areas with poor access to health services. Other high-risk groups are women during pregnancy, and non-immune travelers, refugees, displaced persons and laborers entering endemic areas. Malaria epidemics related to political upheavals, economic difficulties and environmental problems also contribute in the most dramatic way to death tolls and human suffering.
Malaria kills one child every 30 seconds. This preventable disease has reached epidemic proportions in many regions of the world, and continues to spread unchecked. In absolute numbers, malaria kills 3,000 children per day under five years of age. It is a death toll that far exceeds the mortality rate from AIDS. African children under five years of age are chronic victims of malaria, suffering an average of six bouts a year. Fatally-afflicted children often die less than 72 hours after developing symptoms. In those children who survive, malaria also drains vital nutrients, impairing their physical and intellectual development. Malarial sickness is also one of the principal reasons for poor school attendance.
In malaria endemic parts of the world, a change in risk of malaria can be the unintended result of economic activity or agricultural policy that changes the use of land (e.g. creation of dams, irrigation schemes, commercial tree cropping and deforestation). Global warming and other climatic events such as El Niño also play their role in increasing the risk of disease. El Niño events have had an impact on malaria because the associated weather disturbances influence mosquito breeding sites, and hence the transmission of the disease. Many areas have experienced dramatic increases in the incidence of malaria during extreme weather events correlated to El Niño. Moreover, outbreaks may not only be larger, but more severe, as populations affected may not have high levels of immunity.
In today's international world, the phenomenon of "airport malaria," or the importing of malaria by international travelers, is becoming commonplace. The United Kingdom, for example, registered 2,364 cases of malaria in 1997, all of them imported by travelers. "Weekend malaria," which happens when city dwellers in Africa return to their rural settings, is also becoming an increasing problem.
By Professor Paul Henri Lambert
First published 9 December 2003
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