Molecular biology of varicella zoster virus.

Varicella–zoster virus (VZV), also known as human herpesvirus 3 (HHV3) belongs to the herpesvirus family (Herpesviridae). This classification is based on the morphological characteristics of the virus and its physical and chemical properties. The Herpesvirus Study Group of the International Committee on the Taxonomy of Viruses (ICTV) divided the members of this family into three subfamilies: Alphaherpesvirinae, Betaherpesvirinea and Gammaherpesvirinea. Based on its host spectrum, the length of the replicative cycle, the cytopathic effect in vitro and the particularities in the establishment of latency, VZV together with herpes simplex virus type 1 (HSV1; HHV1) and type 2 (HSV2; HHV2) were grouped into the subfamily of Alphaherpesvirinae. Moreover, by its genome organisation, VZV was classified into the genus vari-cellovirus, whereas HSV was classified into the genus simplexvirus, for overview see [1]. Though symptoms of an infection with one of these herpesviruses differ strongly from each other, the morphology of the particles and the biological properties are very similar. VZV is characterised by a strongly limited spectrum of infectable host cells, which are, in fact, exclusive cells of human or simian origin. An important characteristic of herpesviruses is the architecture of the virion. Its size varies between 120 and 300 nm and is described to have a polygonal or round shape with a clearly visible central dot [2, 3]. Until now, it is not exactly known, how many polypeptides are involved in the assembly of the virion, but an average of 30–35 is reported. The virion is structured by four distinct components: envelope, tegument, capsid and core with the genome (fig. 1a).