The genomes of all paramyxoviruses range between 15 and 19 kb in length and contain 6-10 genes that encode up to 12 different proteins [11] . For members of subfamily Paramyxovirinae, efficient RNA replication requires that the nucleotide (nt) length of the genome is an even multiple of six, known as 'rule of six', reflecting the precise packaging of the polynucleotide in the nucleocapsid [12] . The genomes of APMVs are very similar in organization. All the members contain six genes in the order of 39-N-P-M-F-HN-L-59 with the exception of APMV-6, which contains an additional small hydrophobic protein (SH) gene in its genome. APMVs encode a nucleocapsid protein (N), a phosphoprotein (P), a matrix protein (M), a fusion protein (F), a hemagglutininneuraminidase protein (HN), and a large polymerase protein (L). Two additional proteins called, V and W, are produced by RNA editing of the P gene. The F and HN proteins form spike-like projections on the outer surface of the viral envelope and are the neutralizing and protective antigens of NDV. Significant sequence divergence in these two proteins exists among APMV serotypes [6] . The HN protein possesses receptor-binding and neuraminidase activity; whereas, the F protein is directly involved in membrane fusion which is necessary for the entry of the virus. Homotypic interactions between the HN and F proteins are hypothesized to control initiation of the fusion process for most paramyxoviruses [13, 14] . The M protein forms the inner layer of the envelope and plays a key role in assembly by interacting with the HN and F proteins as well as ribonucleocapsid [15, 16] .