Genome-wide analysis of circulating fowl adenovirus E serotype 8b in poultry of Bangladesh.

Fowl adenoviruses (FAdVs), particularly serotype E (FAdV-E), pose a significant threat to commercial poultry worldwide by causing inclusion body hepatitis (IBH) and resulting in substantial economic losses. This study presents the first comprehensive whole-genome sequencing and characterization of three FAdV-E isolates (Alim_IBH_1006, Alim_IBH_1007, and Alim_IBH_1009) collected from IBH-affected commercial poultry in 2024. All genome assemblies were obtained using Illumina sequencing, with genome sizes of 43,686-44,092 bp in length and of GC content (58 %) at a range between 36 and 38 open reading frames (ORFs). These features are consistent with the structures of FAdV-8b (serotype E), which include distinctive inverted terminal repeats (ITRs). Nucleotide identities were 98.79 % to 99.23 % to a Malaysian FAdV-8b strain (UPM T27; PP153927) based on BLAST and pairwise analyses. The identification of the isolates with each other varied between 100.00 % and 96.74 % to 97.51 % with the FAdV-E reference (NC_014969.1), while those with non-E serotypes were much lower (≤78.66 %). Dot plot alignments supported extensive collinearity and conservation with the Malaysian reference, with most observed alterations explained as point mutations. The study conducted phylogenetic analyses of whole genomes, DNA polymerase, and hexon genes, confirming that the Bangladeshi isolates were within FAdV-E and clustered with 8b strains from Malaysia (UPM T27), China, and Peru, suggesting regional transboundary circulation. Using RDP4 for recombination analysis, a high number of significant events were detected between parental strains KU517714 and OL456208 (one large event at approximately 33,026-35,994 bp), and PQ179264/KU517714 are possibly involved in the evolution of FAdV-E by recombination. The results provide important baseline genomic information for FAdV-E serotype 8b in Bangladesh. While these local isolates highlight genomic features and recombination events, continuous large-scale nationwide surveillance across diverse poultry regions will be necessary to fully map the prevalence and genetic diversity of circulating strains.