Molecular evolution of the Newcastle disease virus matrix protein gene andphylogenetic relationships among the paramyxoviridae

Matrix (M) gene sequences for recent field isolates and older reference New castle disease viruses (NDV) were examined to determine phylogenetic relati onships and population trends among these viruses. Overall, the M gene has a majority of synonymous nucleotide sequence substitutions occurring among NDV isolates. However, several predicted amino acid changes in the M protei n of specific NDV isolates have occurred that correlate to phylogenetic rel ationships. Nucleotide substitutions in these codons have a greater number of nonsynonymous base changes. The NDV isolates arising since the 1970s bel ong to a population of viruses that expanded worldwide at an exponential ra te. These viruses may have their origins in free-living birds, are present worldwide, and continue to circulate causing disease in poultry. A specific NDV lineage composed of virulent isolates obtained in the US prior to 1970 appears to no longer exists among free-living birds or commercial poultry. However, "vaccine-like" viruses are common in the US and continue to circu late among commercial poultry. Based on M protein amino acid sequences, NDV separates as a clade most closely related to morbilliviruses and not with their current designated category, the rubulaviruses among the Paramyxoviri dae. Consequently, avian paramyxoviruses should have their own taxonomic su bfamily among the Paramyxovirinae. (C) 2000 Elsevier Science B.V. All right s reserved.