Abstract Title
High Pathogenicity Avian Influenza H5N1 Outbreak in a Layer Flock Vaccinated with Multiple H5 Vaccines
Abstract
This study describes an outbreak of high pathogenicity avian influenza virus (HPAIV) H5N1 in a 15,000-bird flock of brown layer chickens (170 days old) with a four-dose vaccination history using H5N1/H5N8 commercial vaccines administered at 17, 50, 100, and 125 days. Despite this vaccination protocol, H5N1 infection was confirmed approximately seven weeks after the fourth vaccination by RT-qPCR, virus isolation, and sequencing of the HA and NA genes. Clinical manifestations included reduced feed intake, decreased production, and cumulative mortality reaching 35% over 52 days.
Hemagglutination inhibition (HI) testing with various H5 antigens showed variable antibody titers (geometric mean: 4.0 to 9.1 log2), suggesting inconsistent immunity post-vaccination and infection. Sequence and phylogenetic analyses revealed close genetic similarity to circulating H5N1 strains in Egypt, with multiple mutations in the HA head domain, particularly near immunogenic epitopes and receptor binding sites.
These results highlight significant challenges in controlling HPAIV in vaccinated layer flocks, where current vaccination may be inadequate to prevent virus transmission and high mortality rates. Enhanced vaccine strategies, biosecurity measures and stringent monitoring are essential for more effective outbreak management in poultry farms.
Hemagglutination inhibition (HI) testing with various H5 antigens showed variable antibody titers (geometric mean: 4.0 to 9.1 log2), suggesting inconsistent immunity post-vaccination and infection. Sequence and phylogenetic analyses revealed close genetic similarity to circulating H5N1 strains in Egypt, with multiple mutations in the HA head domain, particularly near immunogenic epitopes and receptor binding sites.
These results highlight significant challenges in controlling HPAIV in vaccinated layer flocks, where current vaccination may be inadequate to prevent virus transmission and high mortality rates. Enhanced vaccine strategies, biosecurity measures and stringent monitoring are essential for more effective outbreak management in poultry farms.
Co-Author(s)
Ahmed H. Salaheldin1, Juliane Lang2, Hatem S. Abd El-Hamid3, Elsayed M. Abdelwhab2
1Department of Poultry Diseases, Faculty of Veterinary Medicine, Alexandria University, Alexandria, Egypt
2Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Suedufer 10, 17493 Insel Riems-Greifswald, Germany
3Faculty of Veterinary Medicine, Damanhur University, Damanhur, Egypt
Abstract Category
Diagnostics, vaccination, or other mitigation strategies for poultry and wildlife