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There are three ways in which susceptibles may be exposed to endemic diseases which cause subsequent epidemics or increased levels of disease after disaster. Briefly, this occurs through the migration of rural populations to congested areas; the migration of urban populations to rural areas; and the immigration of susceptibles into areas affected by the disaster. Anticipating these problems and implementing preventive measures require an appreciation of the patterns of disease in the countries stricken by disaster. Migration of rural populations to congested areas In medieval times, the privileged classes tried to avoid the effects of epidemics by fleeing the pestilential cities. The present pattern of reaction to drought, civil disturbance, and many natural disasters is one in which populations congregate for food, safety and medical attention. In general, the more rural and isolated are such migrants, the greater is their susceptibility to common communicable diseases, particularly those transmitted by aerosol or person-to-person contact. Individuals from dispersed communities are also less likely to have received routine childhood immunization. When populations migrate from highlands to camps or population centers at lower altitudes, the risk of vector-borne diseases not transmitted at higher elevations is also added. Migration of urban populations to rural areas More rarely, urban populations may be forced by civil disturbance, an earthquake or a hurricane to move to a rural environment. In so doing they may be exposed to vector-borne diseases, in particular to malaria. The destruction of Managua by earthquake in 1972 was such an event in the Americas (16). The severity of chloroquine-resistant falciparum malaria among Kampouchean refugees is another recent example of acquisition of communicable disease through urban-rural migration. The refugees, first expelled from population centers to rural areas with low malaria indices, then migrated to the Thailand border through holoendemic areas (17). Immigration of susceptibles to affected areas The poorly briefed or underprovisioned international relief worker is the most obvious type of susceptible entering an area affected by disaster. During the Nigerian Civil War a decade ago, this was a serious enough problem that the effectiveness of some foreign medical teams was jeopardized. Failure to appreciate the risk of malaria and/or unwillingness to take chemosuppressive drugs (e.g., chloroquine) caused several cases of the disease, which included cerebral malaria and one fatality. One group, assigned to Biafra, neglected to obtain prophylactic gammaglobulin, and before it could be flown in, members of the team were incapacitated by infectious hepatitis (18). Established relief agencies have long been aware of the risk of disease which susceptibles incur, but they do encounter difficulty convincing skeptical, inexperienced and unsupervised volunteers of the dimensions of the problem. Ad hoc voluntary groups are usually established in the aftermath of a particular major disaster and are also formed in donor countries with special geographic interest in the affected nation. Organizers and their medical staff of ad hoc groups should consult the more experienced agencies or one of the excellent manuals about preserving the health of travelers to the tropics (19-20).
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