Genetic analysis of the complete haemagglutinin (HA) gene of fourteen Nigerian avian influenza isolates showed multiple basic amino acids at the cleavage site (321PQRERRRK del R*GLF333), characteristic of highly pathogenic avian influenza (HPAI). Substitution of Gln to Lys at position 322 (H5-specific numbering) was identified in one isolate. In some isolates, amino acid substitutions were observed across the HA gene, however the receptor binding, antigenic and glycosylation sites were conserved in all. Phylogenetic analysis revealed two clusters of the HPAI H5N1 clade 2.3.2.1c. Cluster I has close genetic relatedness (97.8-99.8%) with viruses circulating in some West Africa countries. Cluster II shared close identity (98.9-100.0%) with isolates from Europe, Côte d'Ivoire and Niger and viruses from this cluster were detected in five of the eleven states investigated in Nigeria. In view of the continuous HPAI outbreaks being recorded in Nigerian poultry and the zoonotic potential of the virus, extensive and continued characterization of HPAI isolates is advocated.
Keywords: Clade 2.3.2.1c; Evolution; H5N1; Haemagglutinin gene; Highly pathogenic avian influenza; Nigeria.