Infection, dissemination, and transmission efficiencies of Zika virus in Aedes aegypti after serial passage in mosquito or mammalian cell lines or alternating passage in both cell types.

Mosquito cell-adapted ZIKV displayed greater in vivo fitness in Ae. aegypti compared to the other viruses, indicating that obligate cycling between disparate hosts carries a fitness cost. These data increase our understanding of the factors that drive ZIKV adaptation and evolution and underscore the important need to consider the in vivo passage histories of flaviviruses to be evaluated in vector competence studies.