Herpes simplex is an enveloped DNA virus (150-200 nm in diameter) belonging to the alpha-herpesviridae. Based on antigenic, biochemical and biologically differences it can be divided into two serotypes, HSV-1 and HSV-2. Man is the only known natural host and source of the virus. HSV type 1 typically causes oral herpes, while HSV type 2 typically affects the genital area. Most of the time, HSV-1 and HSV-2 are inactive, or “silent”, and cause no symptoms, but some infected people have “outbreaks” of blisters and ulcers. Once infected with HSV, people remain infected for life. Herpes simplex viruses are amongst the most common infectious agents of man, and either HSV type appears to be capable of infecting similar body sites. A high percentage of the adult population is seropositive (appr. 90 % HSV-1, in dependence on the socio-economic status 10-30 % HSV-2). Primary HSV-1 infection usually occurs in early childhood (6 to 18 months of age). HSV-2 usually produces mild symptoms, and most people have no recognized symptoms. Persons at risk are children with inherited T-cell deficiencies and patients who are immunosuppressed because of infection (e.g. HIV), transplantation, or cancer therapy. HSV-2 can cause potentially fatal infections in infants if the mother is shedding virus at the time of delivery. - HSV-2 may play a major role in the heterosexual spread of HIV: herpes can make people more susceptible to HIV infection, and HIV-infected individuals more infectious.