Adenoviridae - Overview
Introduction
Adenoviridae are a group of double-stranded DNA viruses with an icosahedral nucleocapsid. Many Adenoviridae have been isolated from mammals and birds, but only a small number of these cause significant veterinary disease. The family consists of four genera: Mastadenovirus, Aviadenovirus, Atadenovirus and Siadenovirus. The Mastadenoviruses include Canine Adenovirus 1 (CAV-1) and Canine Adenovirus 2 (CAV-2), which cause Infectious Canine Hepatitis and respiratory disease respectively. Equine Adenovirus A (also known as Equine Adenovirus 1) is also a Mastadenovirus and causes respiratory signs in horses.
Aviadenoviruses are viruses of poultry and other birds. The genus contains inclusion body hepatitis, quail bronchitis and other avian viruses not associated with a particular disease. The Atadenovirus and Siadenovirus genera contain viruses that until recently were unassigned. These include egg drop syndrome virus and adenoviral splenomegaly of chickens as Atadenoviruses, and turkey haemorrhagic enteritis as a Siadenovirus.
Viral Characteristics
The genetic information of Adenoviridae is conveyed by a single, linear molecule of double-stranded DNA which encodes around 30 proteins. Under the influence of both host and virus-encoded factors, the DNA replicates and is transcribed within the host nucleus, where virion assembly also occurs. Basophilic and/or acidophilic inclusions may therefore be seen in the nucleus of an adenovirus-infected cell.
The virus genome is contained within a non-enveloped icosohedral nucleocapsid, which comprises capsomeres (called hexons) and twelve vertex capsomeres (called pentons). A fibre antigen protrudes from each of the twelve pentons, and this attaches to host cell receptors as well as being a type-specific haemagglutinin. This fibre antigen is a feature specific to the Adenoviridae. The hexon of mammalian adenoviruses contains a cross-reacting group antigen.
Transmission
Adenoviruses are stable to chemical and physical agents and adverse pH conditions, allowing for prolonged survival outside of the body. Aerosol transmission in respiratory droplets is the primary route of spread, but faeco-oral transmission is also possible.