Figure 4.

Plaque size comparison of virus derived from the serum of American crows infected with A, the BIRD1153 West Nile virus strain; and B, TM171-03-pp1; and C, pp3 variants. Daily serum samples from all eight American crows were assayed by plaque assay on Vero cell monolayers. Plaque sizes were differentiated at 37°C and graphically displayed on the basis of the clinical outcome of the infection. Bars represent SDs from the mean. Virus from the serum of decedent American crows are designated in black and surviving crows are designated in white.