9 Herpesviruses

Abstract

In the first chapter of this book we discussed some of the historical evidence which associates herpesviruses with cancer in five sorts of animals: frogs, domestic fowl, guinea pigs, monkeys and man. In this chapter we discuss the structure and taxonomy of herpesviruses, events during productive infections, and recent information about the association between herpesviruses and tumours.

CLASSIFICATION
The nomenclature and classification of herpesviruses is in a state of disorder (Roizman and de-Thé, 1972). Herpesviruses have been named after the host species (equine herpesviruses), after the disease they cause (herpes simplex, pseudorabies, Marek’s disease herpesvirus, etc.), or after their discoverers (Epstein-Barr virus). The herpesviruses have commonly been classified into two groups, depending upon the extent to which infectious virus is released from infected cells (Melnick et al., 1964). Viruses have been assigned to group A if cell-free fluids or extracts readily produce infection in other cells, or to group B if intact cells are required to transmit viral infectivity. However, recent studies suggest that whether or not viral infectivity is strongly cell-associated depends on the cell in which the virus is grown rather than on the virus (Nazerian and Witter, 1970). Classification of herpesviruses into either group A or group B is therefore meaningless.

THE VIRION: STRUCTURE AND COMPOSITION
Herpesviruses are defined as large viruses that have a DNA core, a capsid exhibiting on its surface 162 capsomers arranged in the form of an icosahedron (see Figure 9.1), and a lipid-glycoprotein envelope.

Herpesvirus DNA
Herpesvirus DNA is linear and double-stranded...