Adenoviruses are widespread viruses of mammals and birds. The virions are a T = 25 icosahedron, 70-100 nm in diameter, with fibers projecting from the 12 fivefold axes of the icosahedron (Figs. 2.1 and 2.12). The virion contains 11 proteins, of which 4 are present in the core. The genome of adenoviruses is a linear 36-kb dsDNA. A terminal protein is covalently attached to the 5' end of both strands that serves as a primer during DNA replication.
Adenoviruses are named after adenoids, a gland-like collection of lymphoid tissue in the nasopharynx. They establish a long-term infection in this tissue and were first isolated from human adenoids. Two genera are recognized. The genus Mastadenovirus contains viruses that infect mammals and the genus Aviadenovirus contains viruses that infect birds (Table 6.9). The viruses are species specific and in general will only undergo a complete replication cycle in cells isolated from their native host.
Fifty-one human adenoviruses have been distinguished on the basis of serological reactivity—an adenovirus is considered distinct if it resists neutralization by antisera against the other known adenoviruses. The 51 viruses are simply numbered in order of their isolation and are usually referred to as Ad1, Ad2, etc. The human viruses can be divided into a number of subgroups on the basis of several properties. The six groups, A through F, listed in Table 6.9 are based on serological cross reactions in a hemagglutination-inhibition assay. In this assay, the ability of an antiserum to bind to the virus and prevent it from agglutinating red blood cells is examined. An antiserum against one of the viruses of subgroup A, for example, inhibits hemagglutination by all members of that subgroup but not by members of other subgroups. The grouping in Table 6.9 correlates with a number of other properties of the viruses as well, such as their ability to form tumors in rodents, and is a convenient way of classifying relationships among these viruses.
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