Figure 4: Deletion of the RL1 region affects BV spread in primary mouse cells. Primary murine skin fibroblast cells were prepared, cultured, and infected as described [26]. At low MOI (0.3 PFU/cell) wild-type BV (E90-136) forms plaques by 24 hr PI and rapidly spreads over the next 24 hrs, while the E90ΔRL1 deletion mutant fails to spread after 24 hrs PI.