ENSO-driven climate variability reconfigures the altitudinal frontier of dengue risk in the Andes

Abstract Despite the high burden of dengue in Latin America, high elevations have historically protected megacities such as Mexico City, Quito, and Bogotá. Climate change is expected to shift elevational suitability frontiers, yet the mechanisms governing disease expansion into highland regions and the timescales over which it occurs remain poorly characterized. Using spatiotemporal decomposition techniques, we identified a mechanistic cascade linking (1) the El Niño–Southern Oscillation (ENSO) to local Colombian climate, accounting for ∼85% of interannual temperature variability and ∼53% of rainfall variability, and (2) local climate to dengue dynamics, accounting for ∼66–76% of variation in incidence and ∼44–55% of its altitudinal range. Multiple lines of evidence, including spatial ENSO signatures across Andean ridges, temporal predictive performance, and vectorial-capacity modeling, identified the local temperature expression of the ENSO teleconnection as the dominant driver of transmission. During warm ENSO phases, dengue incidence increases exponentially and transmission expands into higher elevations. This shifts the altitudinal distribution of dengue transmission upward, exposing immunologically naïve populations in highland areas that were previously considered unsuitable. Mechanistically, this altitudinal shift arises because a coherent warming across elevational strata disproportionately increases transmission in highland regions, where small temperature increments produce the largest increase in vectorial capacity. These findings challenge the view that disease expansion is primarily a gradual response to long-term warming and highlight the importance of climate variability for disease projection, attribution, and public health preparedness. Significance statement While increasing mean temperatures are a known threat to the changing landscape of infectious diseases, this study reveals that interannual climate variability can be a more immediate driver of disease burden and expansion. We show that the El Niño phenomenon produces local temperature anomalies in Colombia that exponentially increase dengue cases and extend dengue’s reach into high-altitude areas, potentially exposing millions of immunologically naïve people. This finding is highly relevant to the elevated dengue-free megacities in Latin America, such as Mexico City, Quito, and Bogotá. By shifting the focus from multi-decadal trends to interannual climate variability, this paper provides a methodological blueprint for more accurate predictions of how infectious diseases will behave as our climate becomes increasingly unstable. Competing Interest Statement The authors have declared no competing interest. Footnotes The authors declare no competing interest Expanded revision incorporating additional mechanistic detail and clarifications