**2. Adenoviruses' nomenclature**

This family includes two genera designated based on genetic criteria (*Atadenovirus* and *Siadenovirus*) as well as three genera, in which adenoviruses are combined according to the type of host (*Aviadenovirus*, *Ichtadenovirus*, and *Mastadenovirus*) (https://talk.ictvonline.org/ taxonomy).

Genus *Atadenovirus* presents the newly formed genus which combines adenoviruses with a high relative content of AT-pairs in genomic DNA. This genus includes also adenoviruses of snakes, possums, calves, chameleon, ducks, and lizard.

Genus *Siadenovirus* combines adenoviruses containing at the 5′ end which contains a gene of an enzyme sialidase that cuts off sialic acid residues from the surface glycoproteins of the host cells. These adenoviruses infect frogs and birds.

but it manifests itself much faster (after 4–6 h). The pathogenetic significance of hexons is confirmed by the fact that antibodies against their epitopes demonstrated a neutralizing effect. They may be involved in the development of receptor-dependent endocytosis initiated by

**Figure 1.** Adenovirus structure (from Linda Stannard, of the Department of Medical Microbiology, University of Cape

Introductory Chapter: Human Adenoviruses http://dx.doi.org/10.5772/intechopen.82554 3

A feature of adenoviral DNA is the presence of a terminal protein (TP), which is covalently linked to the 5′ end of each of the DNA strands. One of the possible functions of TP is the DNA attachment to the nuclear matrix after viral genome has entered the nucleus. Due to the interaction of TP, DNA is retained in the form of a ring structure, thus increasing the efficiency of transfection of adenoviral DNA isolated from virions [8]. The size of DNA is (20–25) 103 kDa, which corresponds to approximately 36,000 base pairs. This would be enough for about a dozen medium-sized proteins, but the information capacity of DNA is much more: adenoviruses synthesize about 40 proteins. This is achieved by reading information from both DNA strands and alternative splicing, which provides several types of mRNA based on the primary transcript of one gene. The 13 proteins are included in the mature virion, the rest belong to nonstructural

Antigenic structure of *Mastadenovirus* is represented by three soluble antigens: the hexone A-antigen is common for all serotypes; pentone antigen (B-antigen) is a toxic antigen, it inhibits the action of interferon and increases the severity of associated respiratory infections; and fibril C-antigen is a type-specific which promotes the adsorption of adenoviruses on monkey or rat erythrocytes and causes their agglutination. Manifest forms of the disease cause epidemic serotypes (3, 4, 7, 14, 21) of subgroups B and E. Serotypes 1, 2, 5, and 6 subgroups C cause a latent current, contributing to the formation of chronic tonsillitis and adenoiditis.

components, functioning at the stage of intracellular reproduction of the virus [9].

Clinical forms of adenovirus infection presented in **Table 1**.

fibers, the main target for neutralizing antibodies [7].

**4. Antigenic structure**

Town).

Genus *Aviadenovirus* includes adenoviruses of turkeys, quail, chickens, and a number of other birds. The type species causes the death of embryos and respiratory disease in quails and chickens. Other members of this genus are pathogens of the egg drop syndrome, hemorrhagic enteritis, and hepatitis.

Genus *Ichtadenovirus* has the only characterized representative which infects white sturgeon— *Sturgeon ichtadenovirus A.*

Genus *Mastadenovirus* includes various viruses of mammals: viruses of cows, sheep, deer, pigs, dogs along with all human adenoviruses.

In humans, 57 adenoviruses are known, which are divided into 7 groups (A–G).
