In this study we determined and analyzed the complete nucleotide sequence of the genome of a fowl adenovirus serotype 8 (FAdV-8) isolate and examined its pathogenicity in chickens. The full genome of FAdV-8 was 44,055 nucleotides in length with a similar organization to that of FAdV-1 and FAdV-9 genomes. No regions homologous to early regions E1, E3 and E4 of mastadenoviruses were recognized. Along with FAdV-9, FAdV-8 has only one fiber gene and with regard to sequence composition and genome organization, FAdV-8 is closer to FAdV-9 than to FAdV-1. Moreover, our findings suggest that FAdV-1 of species Fowl adenovirus A as the current type species despite its historical priority is not representative of the genus Aviadenovirus, and that FAdV-8 or FAdV-9 in species Fowl adenovirus E and Fowl adenovirus D, respectively, would be more suitable for that designation. Additionally, pathogenicity of FAdV-8 was studied in specific pathogen free chickens following oral and intramuscular inoculations. Despite lack of clinical signs and pathological changes virus was found in tissues and cloacal swabs of all birds with the highest viral copy numbers present in the cecal tonsils. The highest virus titers in the feces for orally and intramuscularly inoculated chickens were recorded at days 10 and 3 post-infection, respectively.
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