Emergence of dengue at high altitude: characterization of the 2024 outbreak in Cochabamba, Bolivia

Dengue virus (DENV) transmission in Bolivia has historically been restricted to tropical lowland regions, where the primary vector Ae. aegypti is endemic. In recent years, however, the vector has expanded into high-altitude areas. In 2024, Cochabamba, located at ~ 2,550 m above sea level, experienced its largest recorded dengue outbreak. We analyzed data from 9,576 suspected dengue cases reported between January and July 2024, of which 5,923 were laboratory-confirmed. A subset of DENV-positive samples underwent whole-genome sequencing and phylogenetic analysis. Dengue cases were detected in municipalities located at elevations up to 2,719 m, with the highest number reported in Cochabamba city (4,104/5,923, 69.3%; 2,558 m) and the highest incidence observed in Capinota (839 cases per 100,000 population; 2,386 m). Molecular analyses indicated predominant circulation of DENV-2 genotype II clade F.1.1.2. Phylogenetic reconstruction identified two distinct clades closely related to viruses previously detected in southern Brazil, suggesting multiple independent introductions into the department in late 2023. However, the limited availability of genomic data from Bolivia and neighboring countries limits precise identification of the outbreak's origin. This study provides the first characterization of the 2024 dengue outbreak in Cochabamba, an exceptional event of substantial DENV circulation at high altitude, likely facilitated by the expanding geographic range of Ae. aegypti, potentially driven by climate change.