Comparison of growth of wild type (WT) and a small plaque (SP) variant WNV in three vertebrate cell lines. Vero, DF-1, and PDE cells in 6-well plates were infected with Vero cell amplified WT or SP stock virus in triplicate at an MOI of 0.01 pfu/cell, based on Vero cell titers. Both infection and incubation were carried out at the indicated temperatures. Virus was harvested from the medium at various time points after infection, and titers were determined by plaque assay on Vero cells. Symbols represent the mean titer and standard deviation for each time point. The limit of detection (LOD) was 0.7 log10pfu/0.1ml of supernatant of infected cell cultures; in cases where the sample had no detectable virus, a titer of 0.65 log10pfu/0.1ml was used for calculations.