Newcastle disease. Newcastle disease is an acute, rapidly spreading, and usually fatal viral infection of poultry caused by an avian paramyxovirus serotype 1 that meets one of the following criteria for virulence: The virus has an intracerebral pathogenicity index (ICPI) in day-old chicks (Gallus gallus) of 0.7 or greater; or multiple basic amino acids have been demonstrated in the virus (either directly or by deduction) at the C-terminus of the F2 protein and phenylalanine at residue 117, which is the N-terminus of the F1 protein. The term multiple basic amino acids refers to at least three arginine or lysine residues between residues 113 and 116. In this definition, amino acid residues are numbered from the N-terminus of the amino acid sequence deduced from the nucleotide sequence of the F0 gene; 113-116 corresponds to residues 4 to 1 from the cleavage site. Failure to demonstrate the characteristic pattern of amino acid residues as described above may require characterization of the isolated virus by an ICPI test. A failure to detect a cleavage site that is consistent with virulent strains does not confirm the absence of a virulent virus.
9 CFR § 94.0
As used in this part, the following terms shall have the meanings set forth in this section.