Herpes is caused by two viruses -- herpes simplex virus type 1 (HSV-1), and herpes simplex virus type 2 (HSV-2). While statistics vary, research shows that 90% of the population has been exposed to HSV-1, "oral herpes", and 25% of the population aged 25-45 years old in the United States has been exposed to infection with HSV-2, "genital herpes".

HSV-1, the virus responsible for common cold sores, can be transmitted through oral secretions. This is either during kissing, or by eating and drinking from contaminated utensils.

Additionally, HSV-1 can cause genital herpes through transmission during oral-genital sex, thus both strains of the virus may be transmitted by sexual contact. Initial oral herpes infection, however, usually occurs in childhood. It is therefore not classified as a sexually transmitted disease.

While HSV-1 is responsible for only 5% to 10% of genital herpes, HSV-2 causes the majority of genital herpes. HSV-2 can be transmitted through oral or genital secretions. An estimated 86 million people worldwide are thought to have genital herpes.

Because the virus is transmitted through secretions from the oral or genital mucosa, common sites of infection in men include the shaft and head of the penis, the scrotum, inner thighs, and anus. The labia, vagina, cervix, anus, and inner thighs are common sites in women. The mouth can also be a site of infection in both sexes.

Research suggests that the virus can be transmitted even in the absence of clinical disease, so that a sexual partner without obvious genital herpes may still transmit the illness. In fact, asymptomatic spread may actually contribute more to the spread of genital herpes than do active sores.

Various complications are associated with herpes infection. The herpes virus is of special significance to women. It has been implicated in causing cancer of the cervix. The risk increases when HSV is present in combination with human papilloma virus (HPV), the virus responsible for genital warts (condyloma).

For the pregnant women, the presence of either HSV-1 or HSV-2 on the genitalia or in the birth canal is a threat to the infant. Subsequent infection to the newborn infant can lead to herpetic meningitis, herpetic viremia, chronic skin infection, and even death.

The herpes infection also poses a serious problem for the immunocompromised individual (patients with AIDS, undergoing chemotherapy or radiation therapy, or taking high doses of cortisone preparation). These people may suffer infections of various organs including:

• Herpetic keratitis -- herpes infection of the eye leading to scaring within the cornea and eventual blindness.
• Persistent infection of the mucous membranes and skin of the nose, mouth, and throat.
• Herpetic esophagitis -- infection of the esophagus.
• Herpetic hepatitis -- infection of the liver causing inflammation of the liver and eventual liver failure.
• Encephalitis -- a very serious infection of the brain. If untreated, approximately 60% to 80% of those who contract this condition will progress to coma and death within a few days. Those who recover often suffer some impairment, ranging from mild neurological impairment to paralysis.
• Pneumonitis -- infection of the lung causing a life-threatening pneumonia.