Herpes simplex virus (HSV), molecular model. The core protein(central sphere) is usually surrounded by a lipid envelope (cut-away), which fuses with cell membranes permitting entry of the virus into the cell. The virus causes herpes and comes in two forms, type 1 and type 2, and is categorised based on where the infection occurs, for example, oral or genital herpes. HSV is a double-stranded DNA virus, and this genetic information is contained within the icosahedral protein core (capsid) of the virus particle (virion).