Structural and nonstructural protein divergence correlates with strain-specific vector competence for Zika virus

Background Zika virus (ZIKV) emergence in the Americas was driven by Asian-lineage strains, whereas African lineages represent the ancestral form of the virus and remain understudied in terms of transmission potential. Whether genetic differences between viral strains influence their ability to infect and be transmitted by American Aedes aegypti mosquitoes remains unclear. We investigated strain-specific differences in vector competence, host transcriptional responses, and viral genomic variation. Methods Zika virus strains representing Neotropical (Honduras) and Old-World (Senegal) lineages were orally administered to Ae. aegypti mosquitoes via infectious blood meals. Vector competence was assessed at 14 days post-infection by quantifying infection, dissemination, and transmission using RT-qPCR targeting the NS1 gene. RNAseq was performed on infected mosquitoes to evaluate strain-associated transcriptional responses, followed by differential expression analysis. Results Dissemination was markedly higher for the Neotropical strain, as was transmission. Viral loads were significantly higher in whole bodies, legs, and saliva of Neotropical-infected mosquitoes. Neotropical infection suppressed immune- and barrier-associated genes. We observed nucleotide divergence between isolates; the Neotropical strain harbored three nonsynonymous substitutions (Envelope, NS1, NS2A), whereas the Old-World strain retained a single NS2A substitution. Infection did not alter secondary blood-feeding success but significantly reduced fecundity especially among the population exposed to the Neotropical strain. Conclusions The evaluated Neotropical and Old-World ZIKV isolates exhibit markedly different transmission efficiencies in Mexican Ae. aegypti . Limited amino acid variation in structural and replication-associated proteins, together with strain-specific host gene modulation, may contribute to the enhanced transmission potential of the Neotropical isolate. These findings highlight specific viral genetic backgrounds as critical determinants of intra-vector dynamics and transmission risk.