How do HSV-1 and -2 differ?

HSV types 1 and 2 are very closely related, sharing approximately 50% homology in their genetic composition. As expected, many of their viral proteins are also similar (known as type-common), although each type also produces unique proteins (type-specific). Immunohistologic techniques can be used to distinguish these type-specific proteins and differentiate HSV-1 from HSV-2 in clinical situations. Serologic testing that can accurately identify and differentiate antibodies to HSV-1 versus antibodies to HSV-2 is now also available (glycoprotein G type-specific assays). HSV-1 is usually associated with oral herpes and HSV-2 with genital herpes, although each virus can affect both sites. HSV-1 cannot be differentiated from HSV-2 based on the appearance of the skin lesions alone.