Malaria risk on the Amazon frontier

Abstract

Frontier malaria is a biological, ecological, and sociodemographic phenomenon operating over time at three spatial scales (micro/individual, community, and state and national). We explicate these linkages by integrating data from remote sensing surveys, ground-level surveys and ethnographic appraisal, focusing on the Machadinho settlement project in Rondônia, Brazil. Spatially explicit analyses reveal that the early stages of frontier settlement are dominated by environmental risks, consequential to ecosystem transformations that promote larval habitats of Anopheles darlingi. With the advance of forest clearance and the establishment of agriculture, ranching, and urban development, malaria transmission is substantially reduced, and risks of new infection are largely driven by human behavioral factors. Malaria mitigation strategies for frontier settlements require a combination of preventive and curative methods and close collaboration between the health and agricultural sectors. Of fundamental importance is matching the agricultural potential of specific plots to the economic and technical capacities of new migrants. Equally important is providing an effective agricultural extension service.

Fig. 1.

Location and physical structure of the Machadinho settlement project, Rondônia state (RO), Brazil. The traditional “fish-bone” pattern of settlements was replaced by an irregular land division that accounts for the local hydrology and topology, resulting in plots with frontage to roads and rear to a natural source of water. States portrayed in the map: AC, Acre; AM, Amazonas; PA, Pará; RO, Rondônia; MT, Mato Grosso.

Fig. 2.

Subareas of malaria risk and EWR as a function of GoM scores (g). (A) 1985. (B) 1986. (C) 1987. (D) 1995. The number and delineation of subareas were chosen to reflect distinct spatial patterns of EWR, revealed by cluster analysis and spatially estimated EWR (for technical details, see the supporting information, which is published on the PNAS web site).

Fig. 3.

Illegal deforestation of ≈33.5 km² in size that occurred at the southeastern portion of Machadinho.

Fig. 4.

Man-made environmental transformation in Machadinho in 1985 and 1986. The percentage of cleared area is given by Landsat thematic mapper images. Plots with bold yellow borders are those included in the field survey.