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MALARIA: Obstacles and Opportunities
WHERE WE ARE TODAY
Despite advances in the understanding of the pathogenic and clinical aspects of malaria, clinicians still do not know why some people tolerate malaria infections with few or no symptoms, whereas others are severely affected. Indeed, it remains a mystery why some people die of malaria but others do not.
Clinical Aspects of Malaria
It is important to distinguish between the disease caused by malaria parasites and the frequently asymptomatic infection caused by the same parasites. It is important to recognize that one may be infected without having the disease. The disease affects individuals who lack certain anti-illness immunity factors acquired by exposure to malaria or conferred by maternal antibodies transferred across the placenta (World Health Organization, 1990). The specific components of this immunity have yet to be determined, but at-risk groups include those in whom immunity has not yet developed (young children in endemic areas, travelers, and military personnel) and those in whom established immunity has lapsed (pregnant women, inhabitants of an endemic area who leave and then return, and residents of an area in which a successful malaria control program has stopped). Any one of four species of malaria parasite can cause illness, but Plasmodium falciparum causes almost all severe and complicated disease. Malarial illness is frequently several different, often overlapping syndromes.
Among the best known and serious complications of severe malaria, occurring particularly although not exclusively in children, are cerebral malaria, hypoglycemia, and anemia.
Cerebral Malaria Cerebral malaria can be defined as altered consciousness in a patient who has P. falciparum parasites in the blood and in whom no other cause of altered consciousness can be found (World Health Organization, 1990). Cerebral malaria is frequently the only manifestation of a severe falciparum infection in children (Molyneux et al., 1989a); adults with the syndrome commonly have problems in other organ systems, usually the lungs and the kidneys (Warrell, 1987). Between 10 and 50 percent of people with cerebral malaria die, depending on the level of endemicity, how the syndrome is defined, the level of care available, and the age of the patient (Rey et al., 1966; Bernard and Combes, 1973; Stace et al., 1982; Warrell et al., 1982).