Antigenic epitope and phylogenetia analysis of Newcastle disease virus isolated from ducks

Twenty seven NDV isolates were recovered from tracheal and cloacal swabs of clinically healthy ducks in a scaled farm.Two HN monoclonal antibodies(MAbs) were used to analyze the antigenic epitope of these isolates.The HN gene and the variable region of F gene (47-420 bp) of four isolates were sequenced.All the isolates were recognized by MAb C3-B7 in HI test,but the reactions were negative between these isolates and the MAb 1E5.Based upon phylogenetic analysis of a 374 bp region of F gene,four isolates related to lentogenic class Ⅰ viruses,with nucleotide sequences identities of 99.2%-100%.There were 0.9%-9.9% nucleotide differences between the isolates and other class Ⅰ virus,whereas there were 38.5%-41.7% nucleotide differences between the isolates and class Ⅱ viruses.The amino acid sequences of the F protein cleavage sites in these isolates were 112-ERQERL-117.The full length of HN gene of these isolates was 1 851 bp,coding 585 amino acids.The homology analysis of the nucleotide sequence of HN gene indicated that there were 2.0%-4.2% nucleotide differences between the isolates and other class Ⅰ viruses,whereas there were 29.5%-31.6% differences between the isolates and class Ⅱ viruses.The results shows that these isolates do not appear to be phylogenetically related to the vaccine strain(LaSota) and further work should be done to find the source of these isolates.