Genital herpes lesions (blisters) on a penis and close-up view of Herpes simplex virus II, computer illustration. Genital herpes is caused by infection with the Herpes simplex virus (HSV). The herpes viruses are amongst the most common human viral parasites. HSV-I infections are implicated in cold sores that affect the mouth. HSV-II is the cause of genital herpes and can affect the area around the genitals, including the buttocks, thighs and anus. Both types are spread by direct contact and during sexual intercourse. The sores formed in the primary (initial) infection may be very painful and may be accompanied by systemic illness. The sores gradually heal but the virus remains latent in adjacent nerves; subsequent attacks tend to be less severe.