Figure 1. Quantitation of yellow fever virus by focus forming assay (FFA).

This representative photograph shows the results of a FFA performed using uninfected Vero cells (top row) or Vero cells infected with YFV-17D (bottom left) or YFV-Dakar (bottom right). At 3 days post-infection, the monolayers were fixed and stained with anti-YFV Mab, 3A8.B6, and infectious foci were identified by addition of detection reagents as described in the methods. No focus forming units (FFU) could be detected in the YFV-Dakar-infected wells at 3, 7, or 10 days after infection with >100 infectious units of virus as determined by TC-LDA. The data is based on 4 experiments, each with similar results.