Figure 1. Zika virus RNA load levels in human brain and placental tissues. The scatter plot graph shows the relative levels of Zika virus RNA in formalin-fixed, paraffin-embedded tissue sections, which were quantified by real-time quantitative reverse transcription PCR by using primer-probe sets for Zika virus envelope gene and β-actin mRNA. β-actin mRNA was used as an internal reference gene that provided a normalization factor for the amount of RNA extracted from a section. The copy number of Zika virus RNA per cell was calculated using β-actin mRNA copy number, which was estimated to be 1,500 copies/cell. The graph shows individual data points and superimposed horizontal lines at the geometric mean, and error bars show the 95% CI for that geometric mean. p values were calculated with nonparametric 1-way analysis of variance (Kruskal-Wallis test) followed by Dunn multiple comparison tests. The relative Zika virus RNA copy numbers for second/third trimester or full-term placentas were statistically significantly lower than those for first trimester placentas or infant brain tissues.