Highly pathogenic avian influenza viruses are circulating in lots of avian species, causing major outbreaks in both wild and domestic poultry. Since its first emergence in 2014, clade 184.108.40.206 H5N8 viruses widely spread in the world resulting in enormous economic losses. In Egypt, the newly emerging high pathogenic avian influenza (HPAI) H5N8 viruses have been detected in domestic poultry and in wild birds since the 2016/2017 winter season. AI H5N8 is cocirculating with LP H9N2 and HP H5N1 in the Egyptian environment. Poultry vaccination strategy in Egypt is based on commercially available H5 vaccines as an essential control policy, while the majority of commercial avian influenza H5 vaccines utilized in Egypt are not effective against H5N8 viruses. The present study included 3 experimental H5N8 inactivated vaccines based on the 2 major antigenic proteins of the currently circulating strain A/chicken/Egypt/Q16684C/2019 (H5N8), and the internal segments of the A/PR/8/1934 (H1N1) virus. Then, the protective efficacy of the three forms of inactivated vaccines (HAH5N8+7PR8, NAH5N8+7PR8 and HA, NAH5N8+6PR8) were compared regarding the parental PR8 virus in vaccinated specific pathogen free chickens. The NAH5N8+6PR8 as well as HAH5N8+7PR8 and HA vaccines showed the highest protection capacity of challenged SPF chickens and were able to elicit the highest titers of virus-neutralizing antibodies. Thus, a continuous active surveillance strategy is needed to determine the most dominant circulating strain and updating of vaccine seed strains.
Avian Influenza Viruses, Egypt, H5N8, Pathogenicity, Vaccine
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