Pathogenicity and genomic characterization of Brazilian fowl adenovirus serotypes 1 and 11

Fowl adenoviruses (FAdVs) are important pathogens affecting poultry worldwide. Different serotypes cause distinct disease syndromes in domestic chickens, including gizzard erosions (GE), inclusion body hepatitis (IBH), and hepatitis-hydropericardium syndrome (HHS). Despite the economic impact, the evaluation of pathogenicity and genomic features of Brazilian isolates has not yet been assessed. This study aimed to investigate the pathogenic characteristics and whole-genome features of two FAdV Brazilian isolates, BRMSA3762 (FAdV-1) and BRMSA3761 (FAdV-11). For this, pathogenicity was evaluated through inoculation of day-old specific-pathogen-free chickens and embryos. Infected birds were macroscopically and histologically examined in trachea, heart, proventriculus, gizzard, liver, pancreas, duodenum, kidney, and bursa of Fabricius. Also, we analyzed viral distribution in tissues and cloacal virus shedding through real-time PCR. Furthermore, whole-genome sequencing enabled phylogenetic reconstruction and recombination analyses. Results revealed that FAdV-1 was pathogenic, causing severe erosions in the gizzard and a slight alteration in the heart tissue, while FAdV-11 exhibited higher virulence and affected several tissues, including pancreas, liver, gizzard, bursa, and heart. Both viruses were detected in all tissues 8 days post-inoculation, and viral excretion through cloaca occurred throughout the entire experimental period. Differences were established in viral titers, with FAdV-11 demonstrating a higher viral load in tissues and cloacal shedding. In addition, both isolates demonstrated to be pathogenic in SPF chicken embryos. Genomic analysis revealed that BRMSA3762 clustered with sequences from other countries in the Americas, showing no evidence of recombination. Surprisingly, BRMSA3761 clustered with sequences isolated in Europe and the Middle East and was identified as a putative recombinant showing a genetic arrangement closely related to Iranian and Lebanese sequences. Collectively, our findings provide important insights into the pathogenicity of Brazilian fowl adenovirus isolates and contribute to the current understanding of their genetic diversity.