Fig. 1: African lineage ZIKV and post-epidemic Asian lineage ZIKV had a fitness advantage versus pre-epidemic Asian lineage ZIKVs in both A129 mice and mosquitoes.

a Experimental design of competition fitness assays. African lineage ZIKV and post-epidemic Asian lineage ZIKV were mixed with pre-epidemic Asian lineage ZIKV at an approximate ratio of 1:1 and these ratios were confirmed by RT-PCR, followed by Sanger sequencing of replicons and polymorphic nucleotide peaks analysis. The ZIKV mixture was fed to mosquitos through an artificial membrane or a A129 mouse at the viremia peak 3 days post-infection. Mosquitoes were sacrificed after 14 days of incubation, the ZIKV population amplified by RT-PCR, and the amplicon Sanger-sequenced. Mouse blood and organs were collected 3 or 8 days post-infection, respectively. All mosquito and mouse specimens were subjected to RT-PCR amplification and Sanger sequencing to compare the ZIKV strain ratio after competition, and each point represents a single mosquito or mouse sample. Relative fitness values were compared among multiple competition replicates to determine if fitness of the competitors differed. Figure adapted from Fig. 1a in Ref. ¹⁴. b Fitness comparison between African (Dakar 41525), Asian pre-epidemic (FSS13025), and American (PRVABC59) ZIKV strains in A. aegypti. The relative replicative fitness value w was analyzed according to w = (f0/i0), where i0 is the initial ratio of the Dakar 41525 or PRVABC59 competitor to the FSS13025 strain, determined from Sanger sequence electropherogram peaks, and f0 is the final ratio. c, Fitness comparison of African (Dakar 41525), Asian pre-epidemic (FSS13025), and American (PRVABC59) ZIKV strains in mouse viremia, using the same method as for b. d Fitness comparison of African (Dakar 41525), Asian pre-epidemic (FSS13025), and American (PRVABC59) ZIKV strains in mosquitoes after feeding on the viremic mice shown in c, using the same method as for b. b–d, The distribution of the model-adjusted means is illustrated by catseye plots with shaded ± standard errors (SE) overlaid by scatterplots of individual relative fitness values shown on the log (base-10) scale such that comparisons are against a null value of 1. N, numbers represent biologically independent samples shown on the top of each figure. Source data are provided as a Source Data file. b, d, The results were pooled from 3 independent repeats. c The results were collected from a single experiment.