Molecular surveillance of avian influenza A (H5N6) virus in Quangbinh province, Vietnam

The haemagglutinin (HA) gene of highly pathogenic (HP) avian influenza H5Nx viruses (AIVs) has undergone continuous evolution, generating emerging reassorted subtypes and clades. Vietnam has been experiencing HPAI outbreaks since 2003, H5N1 and H5N6 virus infections resulted in culling millions of poultry. This paper presents the results of an active AIVs surveillance in domestic poultry, free-grazing domestic ducks and wild waterfowl in QuangBinh province, Vietnam from September 2015 through March 2018. A total of 452 pool cloacal swabs were analysed by real-time RT-PCR (rRT-PCR). The positive rates of the H5 subtype AIVs were 1.8% of chickens, 5.7% of ducks, and 11.1% of wild birds. Most of H5N6 AIVs were identified from apparently healthy domestic ducks and wild waterfowl (grey heron). Molecular analysis of ten H5N6 AIVs detected in 2016-2018 showed that these viruses have the basic amino acid motif at the HA1-HA2 cleavage site associated with HPAIV and belonged to the clade 2.3.4.4.c. H5N6 HPAI detected in wild waterfowl determined the possibility of virus transmission between wild and free-grazing domestic ducks in QuangBinh. This type of study is very novel in QuangBinh province. Surveillance in wild and domestic birds should be implemented for early detection of the virus and efficient control of its spread in this area.