Fowl adenoviruses cause Inclusion Body Hepatitis, a worldwide problem
[Excerpts of presentations by Saidul Haque and colleagues at Auburn University, USA, during the 2026 International Poultry Scientific Forum]
Fowl adenoviruses (FAdV) are globally distributed poultry pathogens causing economically significant diseases, especially Inclusion Body Hepatitis (IBH). In the United States, the incidence of IBH and the detection of FAdV, particularly FAdV species Eserotypes such as 8b are increasing, highlighting a growing regional and national concern. Despite endemic circulation, molecular and pathological characterization of US field strains remains limited.
This study aimed to characterize the molecular and pathogenic features of five FAdV isolates (four from Alabama, one from Georgia) collected from clinical IBH cases between 2024-2025. Isolates were propagated in specific-pathogen-free chicken embryos, DNA was extracted, and the hexon gene was sequenced. Partial hexon gene sequencing identified all isolates as FAdV-E serotype 8b.
Phylogenetic analysis revealed a monophyletic clade with two internal sub-lineages, suggesting multiple co-circulating lineages. Comparative analysis indicated high nucleotide identity with global FAdV-E/8b strains from Turkey, Israel, Bangladesh, Indonesia, Pakistan, Uganda, and Peru.
In vivo embryo inoculations revealed variable lesion severity, including multifocal hepatic necrosis, hemorrhage, renal necrosis, chorioallantoic membrane thickening, edema, and stunted growth. In vitro, primary chicken embryo kidney and liver cells exhibited consistent cytopathic effects.
These findings confirm FAdV-E 8b as the predominant serotype involved in recent southeastern US IBH cases and demonstrate significant pathogenic variation among closely related isolates. This underscores that genetic similarity in the hexon gene does not uniformly predict virulence, highlighting the need to integrate molecular data with phenotypic assessments. This study emphasizes the importance of continuous surveillance, expanded genomic characterization, improved understanding of genotype-phenotype relationships, vaccine development, and enhanced biosecurity to mitigate the growing threat of FAdV to US poultry production.
