To measure virus replication, infected samples were analyzed by plaque assay at various times post-infection. To measure cell-free virus titer from infected cultures, supernatants were collected every six days of culture and analyzed by plaque assay. Samples were thawed, serially diluted, and plated onto NIH 3T12 cells in 12 well plates in triplicate. Infection was performed at 37uC for one hour. Cells were overlaid with a 1:1 mix of DMEM and carboxymethylcellulose plus fungizone (final concentration 250 ng/mL). Plates were incubated for seven days at 37uC. On day seven, carboxymethylcellulose was removed, and plates were stained with 0.35% methylene blue in 70% methanol and rotated for 15-20 minutes, before rinsing with water and counting on a light box. All titers were determined in parallel with a laboratory standard.