Sequence analysis, pathogenicity and cytokine gene expression patterns associated with fowl adenovirus infection
The family Adenoviridae consists of five genera, including the genus Aviadenovirus, which infects avian species. The genus Aviadenovirus currently comprises five fowl (Fowl adenovirus A-E), one falcon (Falcon adenovirus A), and one goose (Goose adenovirus) adenovirus species. Fowl adenoviruses (FAdVs) have a worldwide distribution. Some are associated with diseases such as inclusion body hepatitis (IBH), while FAdV species C serotype 4 (FAdV-4) has been associated with hydropericardium-hepatitis syndrome (HHS). In this study, the complete nucleotide sequence of fowl adenovirus serotype 8 (FAdV-8) was determined. The full genome was 44,055 nucleotides (nt) in length, with an organization similar to that of the FAdV-1 and FAdV-9 genomes. No regions homologous to early regions E1, E3, and E4 of mastadenoviruses were recognized Pathogenicity of FAdV-8 and FAdV-4 were studied in specific-pathogen-free chickens following oral and intramuscular inoculations. Pathogenicity was determined on the basis of clinical signs and gross and histological lesions. Additionally, virus shedding and viral genome copy numbers in liver, cecal tonsil, and bursa of Fabricius were determined. The role of interleukins (IL) in the pathogenicity of and immune response to FAdVs is unknown. Therefore, in a chicken experiment, interferon-γ, IL-10, IL-18, and IL-8 gene expression was evaluated following FAdV-8 and FAdV-4 infection. Cytokine gene expression was examined in the liver, spleen, and cecal tonsils. This study explored the ability of fowl adenoviruses to subvert the host cell’s secretion of cytokines in response to infection as an important viral mechanism for immune evasion during infection. Variations in virulence of FAdVs are likely to be determined by the fiber alone as shown by Pallister et al. (1996). Therefore, we compared and analyzed the nt and amino acid (aa) sequences of the fiber gene of pathogenic and non-pathogenic FAdVs representing species groups D (FAdV-11) and E (FAdV-8). According to our data, virulence might not be associated only with sequence of the fiber gene. This work is a continuation of our efforts towards better understanding of the molecular biology of FAdVs and the pathogenesis of the disease, with an emphasis on the role of interleukins, an unknown area.