Herpes simplex type 1 (HSV-1) belongs to a family that includes HSV-2, Epstein-Barr virus (EBV) and Varicella zoster (chicken pox) virus amongst others. HSV-1 and HSV-2 are extremely difficult to distinguish from each other. Members of this family have a characteristic virion structure. The double stranded DNA genome is contained within an icosahedral capsid embedded in a proteinaceous layer (tegument) and surrounded by a lipid envelope, derived from the nuclear membrane of the last host, which is decorated with virus-specific glycoproteins spikes. These viruses are capable of entering a latent phase where the host shows no visible sign of infection and levels of infectious agent become very low. During the latent phase the viral DNA is integrated into the genome of the host cell.