Science Letters

Recent Understanding of the Classification and Life Cycle of Herpesviruses: A Review

Aayesha Riaz,* Murtaz-ul-Hasan, Kifayatullah, Naeem Akhtar

Department of Pathobiology, Faculty of Veterinary and Animal Sciences, PMAS-Arid Agriculture University, Murree Road, Rawalpindi, Pakistan

Abstract

Herpes viruses are widely distributed in nature. The number of the herpes viruses that have been isolated exceeds 200. The core of a typical herpesvirus particle consists of genomic linear double stranded DNA which is wrapped in an icosahedral capsid of T=16 symmetry and has an approximate diameter of 100 to 110 nm. Herpes virus genomes vary in length from 120 to 250 kilobase pairs (kb) and encode between 70-220 open reading frames (ORFs) although the recent characterization of clinical human cytomegalovirus (HCMV) strain suggests that the viral genome has 252 ORFs that may encode potential proteins. The life cycle of herpes viruses is divided into two different stages in the host; the lytic stage and the latent stage. The first step in the typical lifecycle of the herpes viruses is the entry into the host cell. Most of the herpesviruses enter into the host cell by fusion but some also use the endocytic pathway for viral entry. The glycoproteins present in the viral envelope interact with the target molecules present on the host cell membrane and allow the viral capsid and tegument proteins to enter into the cytoplasm of the host cell. The process of HSV virion attachment on the host cell surface involves the interaction of five different glycoproteins. Transcription of herpes virus's genes occurs via a highly regulated expression cascade. The objective of this review was to describe the recent understanding of the classification and life cycle of herpesviruses.