Cross-reaction with NDV by sera raised against the other APMV serotypes, from the experiment in Figure 1, was determined by NDV-specific ELISA (A), HI (B), and neutralization (C) assays. Antibody titers are expressed as means with SEM (standard error of the mean) indicated, and titers above the dotted lines were considered positive. The NDV ELISA (A) was a commercial kit involving whole virus antigen, and antibody titers are expressed as a S/P (sample/positive) ratio. The NDV-specific HI (B) and neutralization assays (C) were determined using the NDV strain Texas-GB, and titers are expressed as reciprocal log2. Statistical differences by one-way ANOVA non-parametric test had shown a significant P value of P< 0.0001 for these three tests.