Resurgence of malaria in protected and rural areas after successful control program in a Brazilian Amazon municipality

Malaria eradication requires reducing transmission in endemic areas and maintaining these reductions in areas where elimination has been achieved. In Altamira, a municipality in the Xingu Basin of the Brazilian Amazon, a malaria control program was implemented during the construction of the Belo Monte Dam which eliminated local malaria cases, but resurged in rural areas after these efforts ceased. To elucidate different drivers of malaria transmission in Altamira, before (2006-2012) and after (2017-2020) the construction of Belo Monte Dam and the localized malaria control program, we analyzed annual notified malaria cases alongside geospatial variables including forest edge, population size and travel time to urban centers. Due to the low incidence, malaria case data was clustered based on the geographic proximity of health centers. A total of 17,578 malaria cases were reported in Altamira between 2006 and 2020. Malaria cases exceeded 1,200 per year prior to dam construction, then dropped below 100 during construction, resurging to over 700 cases by 2020 predominantly in rural clusters. Using generalized additive models we found that malaria cases increased significantly with increases in forest edge habitats and local population size, both before and after dam construction, while neither distance to deforestation nor climatic variables explained incidence variation. This study emphasizes that interruptions to control efforts, even when localized, can rapidly reverse gains, and that understanding landscape epidemiology is critical for achieving and maintaining malaria elimination in Amazonian settings.