Recurrent infections tend to be less severe because of existing cellular and humoral immunity from prior exposures. Infection by HSV requires a break in the skin s barrier because of intact skin's resistance to the virus. HSV-1 infections are spread via respiratory droplets or direct exposure to infected saliva. Fluid accumulates between the dermis and the epidermal skin layers and causes vesicle formation. The fluid then is absorbed, scabs formed, and healing completed without evidence of scarring.
Shallow ulcers form after the vesicles rupture on mucous membranes.
Encephalitis develops in 1 per 250,000-500,000 patients per year. Neonatal HSV develops in 1 per 2,000-10,000 live births per year. The risk of maternal transmission is increased if vaginal delivery occurs during the mother's primary infection. Infection occasionally may become life threatening. Patients who are immunocompromised are at increased risk of developing severe HSV infections.