Relationship between the Flooded Area and Cases of Malaria Disease before and after Construction of Jirau Hydroelectric Plant, Madeira River, Brazil

The operation of the Jirau hydroelectric plant, in the Madeira River near Porto Velho, Brazil started in 2013. Increased flooding areas near Jirau dam periodically reach communities with poor sanitation and can result in health problems, as the propagation of tropical diseases transmitted by aquatic vectors. Thus, we investigated the relationship between flooded areas and cases of malaria in Jirau´s Administrative Regions between 1994 and 2015. The flooded area was determined through spectral data (Landsat-5 and Landsat-8 satellite) and the numbers of malaria cases were extracted from the Epidemiological Surveillance Information System database of the Brazilian Ministry of Health. We verified an average flooded area of 770.3 km² before the dam (1994-2013) and 1370 km² after its operation (2014-2015). With linear regression between malaria cases and flooded areas, we verified a negative correlation during the study interval. Despite greater average flooded area after dam operation, the reduction of cases may be a result of several factors such as the imbalance of the parasitic relationship due to microclimatic changes, application of new substances for biological control (like artemisinin derivatives), little time for vector adaptation into new breeding sites, presence of plasmodium asymptomatic carriers, or even gaps or lack of case records in epidemiological databases. We highlight the importance of continuous monitoring of these variables and social control actions coverage expansion to prevent the risk of epidemic cycle occurrence and guarantee health security concerning this tropical disease and its socio-economic consequences.