Expansion of the dengue transmission area in Brazil: the role of climate and cities.

OBJECTIVES: To examine the spatial and temporal patterns of the recent expansion of dengue transmission area in Brazil (2001-2012) with the aim to identify pathways and constraints to dengue diffusion.
METHODS: Synthetic indicators were calculated to characterise timing (year of first dengue outbreak), permanence (number of years with dengue outbreaks) and intensity (outbreak occurrence). The indicators were used to map dengue diffusion and compare cities within different climatic zones, with varying population densities.
RESULTS: Currently, a large portion of the country comprises a dengue transmission area, but cities situated in the mesothermal zone, in the south, and remote areas, in the north, are relatively exempt. Diffusion waves are spread from metropolitan areas towards medium and small cities generating outbreaks in their influence region. However, long-term permanence of transmission depends on the existence of a favourable climate, abundant population and connectivity.
CONCLUSIONS: Large and warm cities sustain and spread dengue viruses, for which specific dengue control measures must be developed. The concentration of outbreaks along climate transition fringes indicates a boundary between two transmission regimes and raises awareness to the effects of ongoing climatic and socio-economic changes.