Avian adenovirus

Aviadenoviruses are adenoviruses that affect birds—particularly chickens, ducks, geese, turkeys and pheasants. There are 28 species in this genus. Viruses in this genus cause specific disease syndromes such as Quail Bronchitis, Egg Drop Syndrome, Haemorrhagic Enteritis, Pheasant Marble Spleen Disease, and Inclusion Body Hepatitis. Avian adenoviruses have a worldwide distribution and it is common to find multiple species on a single farm. The most common serogroups are serogroup 1, 2 and 3.

Transmission

No evidence of transmission from birds to humans has been identified. The virus is mainly spread horizontally by the oro-fecal route, but vertical transmission can occur in serogroup 1. Once it has infected the bird the virus may remain latent until a period of stress, when it may then cause clinical disease.

Clinical signs and diagnosis

Infections are normally subclinical, however clinical disease can occur—especially in young birds as maternal antibody levels begin to wane.
Clinical signs are related to the organ affected.
Signs of gastrointestinal disease include diarrhea, anorexia, melena and hematochezia. Anaemia and dehydration may develop secondary to this haemorrhagic enteritis. Signs of reproductive disease include low egg production/hatching and the laying of abnormal eggs. Adenovirus infection may infect other organs, causing splenitis, inclusion body hepatitis, bronchitis, pulmonary congestion ventriculitis, pancreatitis, or oedema, depending on the species of bird infected.
Diagnosis of aviadenovirus is by histopathology, electron microscopy, viral isolation, ELISA and PCR. In addition, virus antigen can be detected double immunodiffusion. Postmortem examination may reveal a variety of clinical signs relating directly to the organ affected. Specifically, Egg Drop Syndrome can be diagnosed by hemagglutinin inhibition and the virus causes haemagglutination in chickens and ducks.

Treatment and control

Vaccines for HE and EDS are available. Disease incidence may be reduced by minimising stress levels, using appropriate hygiene measures and providing adequate nutrition.

Taxonomy

Aviadenovirus contains the following species, listed by scientific name and followed by the exemplar virus of the species:Aviadenovirus anatidae, Duck adenovirus 5Aviadenovirus anatis, Duck adenovirus 2Aviadenovirus anseris, Goose adenovirus 4Aviadenovirus bubonis, Indian eagle-owl adenovirus 1Aviadenovirus cairinae, Duck adenovirus 4Aviadenovirus cerasi, Duck adenovirus 6Aviadenovirus columbae, Pigeon adenovirus 1Aviadenovirus columbidae, Pigeon adenovirus 2Aviadenovirus falconis, Falcon adenovirus 1Aviadenovirus gallinae, Fowl adenovirus 9Aviadenovirus gallopavoprimum, Turkey adenovirus 1Aviadenovirus gallopavoquartum, Turkey adenovirus 4Aviadenovirus gallopavoquintum, Turkey adenovirus 5Aviadenovirus gruis, Crane adenovirus 1Aviadenovirus hepatitidis, Fowl adenovirus 6Aviadenovirus hydropericardii, Fowl adenovirus 4Aviadenovirus leucophthalmi, Southern Psittacara leucophthalmus aviadenovirus, also called White-eyed parakeet adenovirus 2Aviadenovirus orioli, Black-naped oriole adenovirus, also called Oriolus adenovirusAviadenovirus oti, Eurasian scops owl adenovirus 1, also called Otus scops adenovirusAviadenovirus phalacrocoracidae, Great cormorant adenovirus 1Aviadenovirus podargidae, Tawny frogmouth adenovirusAviadenovirus quintum, Fowl adenovirus 5Aviadenovirus roseae, Psittacine adenovirus 12Aviadenovirus rubri, Psittacine adenovirus 4Aviadenovirus senegalense, Psittacine adenovirus 1Aviadenovirus spinus, Eurasian siskin adenovirus 2Aviadenovirus turdi, Naumann's thrush adenovirus 1Aviadenovirus ventriculi, Fowl adenovirus 1

Structure

Viruses in Aviadenovirus are non-enveloped, with icosahedral geometries, and T=25 symmetry. The diameter is around 90 nm. Genomes are linear and non-segmented, around 35–36kb in length and have a guanine/cytosine content of 53–59%. The genome codes for 40 proteins.

Genus	Structure	Symmetry	Capsid	Genomic arrangement	Genomic segmentation
Aviadenovirus	Polyhedral	Pseudo T=50	Non-enveloped	Linear	Monopartite

Life cycle

Viral replication is nuclear. Entry into the host cell is achieved by attachment of the viral fiber glycoproteins to host receptors, which mediates endocytosis. Replication follows the DNA strand displacement model. DNA-templated transcription, with some alternative splicing mechanism is the method of transcription. The virus exits the host cell by nuclear envelope breakdown, viroporins, and lysis. Birds serve as the natural host.

Genus	Host details	Tissue tropism	Entry details	Release details	Replication site	Assembly site	Transmission
Aviadenovirus	Birds	-	Glycoprotiens	Lysis	Nucleus	Nucleus	Unknown