Herpes (the name is derived from the Greek word meaning "to creep") is actually a family of five viruses:

* Herpes Simplex Type 1. This virus infects an estimated 75 percent of the population, though in most it causes no symptoms. In others, it can cause painful and recurring cold sores and fever blisters, usually in the mouth or on the lips and face.

* Herpes Simplex Type 2. Commonly known as genital herpes, this virus causes skin lesions, usually on the genitals. It is spread by sexual contact with active lesions, which are highly contagious for about 10 days. A pregnant woman with active genital herpes infections is at high risk of infecting her baby with potentially fatal congenital herpes as the baby passes through the birth canal, and should therefore deliver by cesarean section.

* Varicella-zoster. This is the viral agent for chicken pox, which infects about 98 percent of American children. The virus then lies dormant but reawakens in some adults decades later in the form of painful nerve irritations called shingles, as in the case of former president Nixon, reported last week. A bout with shingles usually lasts four to six weeks, but in rare cases, victims suffer lasting or recurring pain.

* Epstein-Barr virus. This is the virus that causes infectious mononucleosis, which produces mild symptoms in children but more severe symptoms in adults, including extreme fatigue, aching joints, sore throat and difficulty swallowing. In rare cases, some symptoms become chronic.

* Cytomegalovirus. This virus infects most people by age 40, but usually with mild symptoms similar to those of a cold. It can cause a range of birth defects, including mental retardation and blindness. In adults over 40, or those with weakened immune systems, the symptoms can be more severe.