In some regions of Africa where the incidence of malaria is relatively low, children tend to get much sicker from the disease. The finding, reported in the 7 June issue of The Lancet, suggests that controlling the spread of malaria--which kills 1 million children in Africa each year--may in some cases make the bug more dangerous.
Although reducing exposure to disease-bearing mosquitoes is known to reduce malaria deaths for 1 or 2 years, the long-term effects of such control strategies have been less clear. Because exposure to the malaria parasite induces some immunity, some experts have argued that reducing exposure--without eliminating the disease--could result in greater numbers of severe cases.
To test this theory, a group of researchers led by Robert Snow of the Kenya Medical Research Institute studied the rates of hospital admissions for children with malaria in five regions of The Gambia and Kenya with different malaria rates. They found that the two regions in which less than half the children were infected with the malaria parasite, or had antibodies to it, had hospitalization rates due to malaria more than 50% higher than those of communities in which about three-quarters of the children were infected. The researchers did not analyze death rates from malaria.
Snow's group speculates that in regions of rampant malaria, almost all children are exposed as infants, when they still get some protection from their mother's antibodies still circulating in their blood. Those early infections induce the children's immune systems to produce their own antibodies, which offer protection from later exposures. In regions with moderate malaria rates, however, many children are not exposed until after their mother's protection has worn off, about 6 months after birth. Malaria epidemiologist Louis Molineaux agrees, adding that children older than 2 years are also at risk for the most severe form of the disease--cerebral malaria.
But Molineaux cautions that the findings should not prompt officials to alter malaria control strategies. "The first priority is to make treatment readily available early in the history of the disease," he says, "but the findings don't justify withholding protection from anybody under any circumstances." Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, agrees, and adds that the study underscores the need for an effective malaria vaccine. "This is an experiment of nature that shows that kids do well when they are immune."