from: Avian Virology: Current Research and Future Trends (Edited by: Siba K. Samal). Caister Academic Press, U.K. (2019) Pages: 283-316.
Avian adenoviruses are ubiquitous worldwide in avian species. Although many of these viruses are isolated from healthy birds, some cause diseases associated with significant economic losses in the poultry industry, including egg-drop syndrome (EDS), inclusion body hepatitis (IBH), inclusion body hepatitis/hydropericardium syndrome (IBH/HPS) in chickens and hemorrhagic enteritis (HE) of turkeys. Avian adenoviruses are classified into three genera based on genome organisation, phylogenetic relationships and host: Aviadenovirus, Atadenovirus and Siadenovirus. The viral genome consists of genus-common and genus-specific genes. Genus-common genes, such as those involved in DNA replication and encoding structural proteins, are conserved and present in all adenoviruses. Genus-specific genes, on the other hand, are unique for each genus. The functions of most early viral genes of avian adenoviruses remain unknown. Some of these genes, such as Gam-1 and ORF22, have functions similar to those described for human adenoviruses - stimulation of cell cycle progression, modulation of apoptosis and counteraction of the host's innate immunity. Studies on virus-host interactions at the molecular level are limited to a few viruses [e.g. fowl adenovirus (FAdV)-1, FAdV-4 and FAdV-9]. The virulence determinants for these viruses are unknown. However, some candidate viral genes associated with virulence have been described in some aviadenoviruses (e.g. FAdV-4 and FAdV-8) and a siadenovirus (duck adenovirus 1). Non-pathogenic aviadenoviruses, such as fowl adenoviruses 1, 4, 8, 9 and 10, have been described as virus vectors for potential use as recombinant poultry vaccines and gene delivery read more ...