Figure 6. Growth kinetics of parental and F protein cleavage site mutant APMV-4 viruses in the brains of 1-day-old chicks.

Ten 1-day-old SPF chicks were inoculated with the indicated parental or mutant viruses via the intracerebral route. Two birds in each group were sacrificed daily until 5 dpi. Brain tissue samples were harvested and virus titers were determined by limiting dilution in DF1 cells and immunostaining with antiserum against the N protein of APMV-4. Each bar represents mean and standard error of the mean of duplicate samples.