The epidemiology of malaria in Rondonia (Western Amazon region, Brazil): study of a riverine population

We report on a longitudinal study concerning the incidence of malaria in a riverine population (Portuchuelo) settled on the riverbanks of Rio Madeira, in the State of Rondonia, Brazil. We found the incidence of malaria to be seasonal, prevailing in the dry months of June and July. The Annual Parasit e Index (API) was 292/1000 inhabitants, almost three times that of the stat e of Rondonia for the same period. In contrast with other studied Rondonian populations, malaria in Portuchuelo was more prevalent in youngsters <16 y ears old, particularly in the 0-1 year age group. Adults were relatively sp ared, particularly those over 50 years. Besides being indicative of indoor transmission, these facts may suggest the existence of a certain degree of acquired resistance to infection and/or of lessened symptoms in older peopl e. Riverine populations are spread over the entire Amazon region where most of its members were born. Due to the permanent presence of malaria among r iverine populations, we are proposing that they may act as perennial reserv es of malaria and, therefore, as sources of infection for migrants or event ual settlers at their vicinity. To date, the opposite view has been general ly held. Anopheles darlingi, the main vector species in the area, is essent ially sylvatic, which contributes to make the control of malaria highly pro blematic. The only hopes for control rest on permanent surveillance and the prompt treatment of patients, which are also problematic considering the v astness of the Amazon region and the remoteness of some of its riverine set tlements. (C) 1999 Published by Elsevier Science B.V. All rights reserved.