Despite difficulties with oral administration and degradation in the digestive tract, peptides may make useful antiviral agents when targeted against viral envelope proteins. Directing inhibitors to viral surface proteins avoids the major difficulty of crossing cellular membranes in order to reach the target. For example, peptide inhibitors of intercellular viral targets, such as proteases or polymerases, would need to cross the cell plasma membrane, and in the case of flaviviruses, possibly internal membrane bound Figure 7 . Quantitative reverse transcriptase PCR virus:cell binding. Virus pre-incubated with either DN57opt or 1OAN1 shows reduced binding to cells compared to control virus without peptide. Pre-incubation of virus with pooled human anti-dengue serum or heparan sulfate similarly shows reduced cell binding. * Indicates a significant difference (p,0.05) from all others by 1-way ANOVA followed by Tukey's posthoc test. doi:10.1371/journal.pntd.0000721.g007