The herpes simplex virus (HSV) is a double- stranded DNA virus. It is a member of the human herpes viruses (herpetoviridae) group. This group includes varicella zoster virus (chicken pox) and Epstein-Barr virus (the virus that causes mononucleosis), among others. There are two types of herpes simplex virus, types I and II. Both HSV I and HSV II can be considered STDs, since they both can be transmitted sexually and both can cause lesions in the genital area. HSV II causes 70 to 95 percent of genital herpes infections. The remaining 5 to 30 percent of genital herpes infections can be attributed to HSV I.
According to a survey of 40,000 Americans conducted between 1988 and 1994, the overall HSV II prevalence rate in the United States is almost 22 percent. Genital herpes is the most common cause of genital ulcers in the world, with 20 million cases diagnosed annually. Unprotected sexual activity, particularly with multiple partners, and being female increases your risk of acquiring HSV II. There are also increased rates of HSV among African American and Latino populations, and those in lower socioeconomic groups.
Transmission of HSV occurs during oral, vaginal, or anal sex when an infected partner passes on the virus through microabrasions in his or her partner's skin or mucosa. The person passing on the herpes needs to be shedding the virus at the time of contact with his or her partner. Typically viral shedding occurs when the infected person is experiencing an outbreak of lesions. However, viral shedding can take place before a lesion erupts, or can take place in the absence of lesions; this is called "asymptomatic shedding." The rate at which an infected person sheds the virus is entirely dependent on the individual, but some studies have shown that an infected person may be shedding the virus asymptomatically 1 out of every 4 days.
Once an epithelial cell is infected in another person, the virus replicates at a high rate. Inside the body the virus invades sensory nerves and takes up residency for the life of the host in their sensory nerve cell bodies in the dorsal root ganglia. Initial infection causes symptoms (see below), but once these symptoms are resolved, the person is at risk for later recurrence of an outbreak.
Primary infection refers to an initial infection with HSV. Fifty to 70 percent of people will develop a fever, aches, and headache in addition to symptoms in the genital region. Genital symptoms may begin as pain, itching, painful urination, vaginal or urethral discharge, and lymphadenopathy and progress to the development of characteristic lesions. The lesions first appear as red bumps or blisters, which evolve into ulcerations before crusting over. They are often painful. At the onset of the infection, the person will be infectious and shedding the virus for up to twelve days. These lesions may appear on the penis, scrotum, buttocks or anus in a man, and on the labia, in the vagina, on the cervix, and on the anus or buttocks in a woman. The lesions may take up to three weeks to heal.
Lesions can also occur on the lips or in the mouth of a person through exposure to oral sex. Lesions that only occur orally on a person may be attributed to HSV I infection, and exist in the absence of having HSV as an STD. HSV I prevalence in the U.S. population is, in fact, widespread. Over 90 percent of adults will be infected with HSV I by the fifth decade of life. There is evidence that prior infection with HSV I lessens the severity of an initial infection with HSV II.