Figure 1. Clinical phenotype and viral replication in naive and DENV-immune Ifnar1^−/− mice inoculated with passaged ZIKV strains.

(A–D, B, and F) DENV2-immune Ifnar1^−/− mice were generated by intraperitoneal injection of 10³ FFU DENV2 S221. Thirty days later, groups of naive (A–D) and DENV2-immune (E–H) Ifnar1^−/− mice (n = 5) were injected intra-footpad with PBS/10% FBS or 10⁴ FFU of unpassaged ZIKV FSS13025 (WT) or ZIKV passaged for 10 cycles through mosquito cells and naive (ZN-p10) or DENV2-immune (ZDI-p10) Ifnar1^−/− mice. Animals were monitored daily for survival (A and E), weight loss (B and F), and clinical score (C and G). Animals that lost >20% of their initial body weight were euthanized.

(D and H) Parallel groups of mice were euthanized 3 days after ZIKV infection, and infectious ZIKV levels in serum and the indicated organs were quantified by FFA (n = 6/group). Data are presented as the mean ± SEM and were pooled from two independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 by the Gehan–Breslow–Wilcoxon test (survival) and the two-tailed Mann–Whitney test (body weights and viral titers).