such regions will necessarily focus on preventing death in young children and nonimmune people coming into the area. In parts of mainland Southeast Asia, however, where forest malaria prevails, exposure to malaria parasites may occur first in young adult males during work-related activities. Antimalarial efforts in these areas will focus on protecting forest workers, and military patrols, and perhaps accompanying family members. The simple observation that in Africa malaria is mainly a childhood disease, whereas in much of Asia and South America it is a disease of young adults, is often overlooked during the planning of control strategies.

Population movement also plays a role in determining the impact of malaria. For example, residents of settled villages (often settled because they are malaria free) are often at lower risk of contracting malaria than are people living in constantly shifting villages, such as members of the hill tribes of Southeast Asia, which practice slash-and-burn agriculture. If the movement of people is organized and predictable, as it is when African nomads routinely visit oases that support malaria transmission, interventions can be put in place during the times when the population is at greatest risk of disease. The role of population density and settlement patterns must also be taken into account. Amazonian Indians, who traditionally live in widely separated villages of low population density, are at much less risk of contracting malaria than are large groups of gold miners, who constantly are shifting to new exploration sites in the same geographic area. The population movement determinant should be considered in decisions on control strategies both to identify populations at greatest risk and to assess the feasibility of a given intervention.

Social, Behavioral, and Economic Considerations Several social, behavioral, and economic factors should bear on decisions as to the most appropriate and cost-effective malaria interventions. These factors, some of which are discussed below, may help determine differential exposure to malaria parasites or the likelihood that effective treatment will be administered early enough to prevent severe disease.

ACCESS TO HEALTH CARE is probably the most important socioeconomic determinant of malarial illness. People in malarious areas who live at great distances from health services, whether governmental, nongovernmental (mission, etc.), or commercial markets and pharmacists, are likely to suffer more from the disease than those who have such services close at hand. Access may be limited by more than distance, however. Close-by health centers that have unreliable drug supplies, have poorly trained and unsupervised staff, or charge fees unaffordable to affected populations are no better than nonexistent or too-distant services. Appreciation of such factors will influence the choice of malaria control interventions.

TYPE OF HOUSING may influence both the risk of infection and the

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