Wolbachia prevalence in Aedes aegypti across five comunas of Medellín, Colombia: Implications for post-release surveillance.

A promising sustainable strategy for reducing arbovirus transmission by the mosquito vector Aedes aegypti is the deployment of individuals transinfected with Wolbachia pipientis, a bacterium that inhibits replication of viruses such as dengue and is being used in population replacement programs aimed at blocking Aedes-borne virus transmission. Between 2017 and 2022, the World Mosquito Program released Ae. aegypti infected with the wMel Wolbachia strain throughout Medellín, Colombia. Long-term Wolbachia surveillance following population replacement requires approaches that balance accuracy and cost while providing reliable information regarding infection persistence in targeted populations. Therefore, we assessed current Wolbachia prevalence in Ae. aegypti, surveying five comunas (geographic administrative units) of Medellín spanning ~32.66 km, using ovitrap collections and field sampling of adult mosquitoes and assessed Wolbachia infection using conventional PCR and quantitative PCR (qPCR) in pooled and individual samples. We found that Wolbachia infection remains widespread across the surveyed areas, with estimated infection frequencies ranging from ~60% to near fixation depending on sampling strategy and molecular detection method. Screening pooled adults emerging from ovitraps using conventional PCR provided a cost-effective method for confirming Wolbachia persistence across sites, whereas qPCR of individual field-captured adults provided more sensitive estimates of infection prevalence. Our results suggest that Wolbachia is broadly established in Ae. aegypti populations in the surveyed areas and demonstrate practical approaches for the long-term surveillance of Wolbachia-based vector control programs.