Molecular characterization and phylogenetic analysis of Newcastle disease viruses isolated in southern Angola, 2016-2018.

Newcastle disease (ND) is a highly contagious viral disease that affects many bird species worldwide. This study presents the results of the molecular characterization and phylogenetic analysis of 15 virulent ND viruses (NDV) isolated from chickens during outbreaks reported in 2016 and 2018, in the provinces of Namibe and Huíla, in southern Angola. A 561-nucleotide fragment of the F gene was amplified by RT-PCR and sequenced for molecular characterization. Results showed that in all isolates the amino acid sequence comprising the cleavage site of fusion protein is characteristic of virulent viruses (RRQKR/F). Blast analysis revealed high similarity (99.2%) between two isolates from Huíla province, HLA4 and HLA6, and strain 5620 (GenBank accession number KY747479) isolated from chickens in the neighboring country Namibia, in 2016. The other isolates investigated are more related (97.0%) with strain 6195 (GenBank accession number KY747480), also isolated in Namibia in 2016. Phylogenetic analysis performed by Maximum Likelihood, Neighbor-joining and Bayesian methods revealed that like the strains isolated in Namibia, the isolates from southern Angola also belong to subgenotype 2 of genotype VII (VII.2). The network analysis revealed that NBA1 isolate from Angola is closer to a common ancestor than the isolates from Namibia, suggesting that transmission of ND viruses occurred from Angola to Namibia.