Reemergence of DENV-3III_C.1 and emergence of DENV-3III_B.3.2 in Ecuador: multiple introductions and dispersal patterns, 2022-2026.

We characterized the reemergence of DENV-3III_C.1, the emergence of DENV-3III_B.3.2, and their phylogeographic spread in Ecuador during 2022-2026 through integrated epidemiologic and genomic surveillance. Lineage DENV-3III_C.1 formed a monophyletic Ecuadorian cluster closely related to Colombian viruses. The earliest sampled Ecuadorian sequence was detected in Esmeraldas, compatible with a possible introduction across the northern border followed by within-country dissemination. Lineage DENV-3III_B.3.2 comprised multiple Ecuadorian clades related to viruses from Colombia, Cuba, and the United States (travel-associated), consistent with independent introductions followed by geographic expansion. These findings reveal distinct transmission histories and support strengthened genomic surveillance at border crossings and other key points of entry.