Adenovirus: Properties of the Virus

Properties of the Virus

◗ Morphology

Adenoviruses show following features:

·           Adenoviruses are double-stranded DNA, nonenveloped viruses measuring 80–110 nm in diameter.

·           The adenovirus genome is a linear double-stranded DNA with terminal protein. DNA contains terminal incorporated lipids of more than 100 base pairs, rendering the single-stranded DNA to form pan-handle-shaped molecules. The viruses have icosahedral nucleocapsid with a diameter of 70–90 nm.

·           Adenoviruses have a characteristic morphology. They are the only viruses having a fiber protruding from each of the 12 vertices of the capsid.

·           The capsid is composed of 252 capsomeres, which con-sist of hexons and pentons. Of these 252 capsomeres, 240 hexons make up the 20 triangular faces of icosahedron and 12 pentons form the bases.

·           An apical fiber, 9–31 nm in length and 62 kDa in molecular mass, projects from each penton. This apical fiber helps to bind specifically adenoviruses to receptor sites on the host cells. The fiber contains the viral attachment proteins and can act as a hemagglutinin. The penton base and fiber are toxic to cells. The type-specific antigens are present in the pentons and also in the fibers.

·           Viruses encode proteins to promote messenger RNA (mRNA) and DNA synthesis including its own DNA polymerase.

◗ Viral replication

Adenoviruses attach to surface of the cells by their fibers, then penetrate the cell, and once inside the cell, uncoat the viral DNA. The viral DNA is then transported into the nucleus of the cell and initiates replication cycle. Host cell DNA-dependent RNA polymerase transcribes the early genes leading to formation of functional mRNA. Then in the cytoplasm, the early mRNA is translated into nonstructural proteins. In the nucleus, after viral DNA replication, late mRNA is transcribed and then translated into structural virion proteins. This is followed by assembly of virions in the nucleus and release of virions by lysis of the cells, but not by budding.

◗ Antigenic and genomic properties

Viral group-specific antigen is present on the inner surface of hexon capsomere. These group antigens can be detected by immunofluorescence or enzyme-linked immunosorbent assay (ELISA). Type-specific antigen is located on other region of the hexon and on the fiber. The fiber protein is the main type-specific antigen. Fiber determinant (gamma) is a type-specific hemagglutinin. Serotypes are identified by neu-tralization test.

◗ Other properties

Adenoviruses are relatively stable and remain viable for about a week at 378C but are readily inactivated at 508C. They are resistant to ether and bile salts. They resist drying, detergents, gastrointestinal tract secretions including acid, protease, and bile, and even mild chlorine treatment.