Influence of chicken breed on pathogenicity evaluation of velogenic neurotropic Newcastle disease virus isolates from cormorants and turkeys.

Three isolates of Newcastle disease virus (NDV) from cormorants and turkeys were classified as velogenic neurotropic NDV (VNNDV) by standard pathotyping procedures in specific-pathogen-free white leghorn and white rock chickens. White leghorns inoculated by eye drop, cloaca, intravenous, or intracerebral routes had a higher frequency of nervous signs and mortality than was observed in similarly inoculated white rocks. Two backpassages in white rocks increased the intravenous pathogenicity index of all three isolates, but none had a value after backpassage that was as high as the classical VNNDV strain Texas GB. The breed of chicken used in standard procedures did influence the numerical values of pathotyping determinations, but the differences between breeds were not large enough to change the pathotype assigned to these isolates.