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. The deletion of an extra six nucleotides in the 5' -untranslated region of the nucleoprotein gene of Newcastle disease virus NA-1 decreases virulence. BMC Vet Res. 2014;10:964 pubmed publisher
..However, rNA-1(-) was more virulent in chickens than geese, as seen by the higher intracerebral pathogenicity index value. ..