Herpes simplex

Definition:

An infection caused by the herpes virus; it is characterized by an eruption of small and usually painful blisters on the skin. See also herpes simplex - oral.

Causes, incidence, and risk factors:

There are two strains of herpes viruses. Herpes simplex virus type 1 (HSV-1) is usually associated with infections of the lips, mouth, and face. It is common in children between 1 and 3 years old and may cause lesions inside the mouth and inflamed gums. It causes cold sores or fever blisters and is transmitted by oral and respiratory secretions (for example, sneezing or coughing can transmit the virus). Herpes simplex virus 2 (HSV-2) is usually associated with genital lesions and is transmitted by sexual contact. Cross-infection of type 1 and 2 viruses may occur from oral-genital sex. Both viruses are contagious and the first symptoms usually appear 1 or 2 weeks after contact with an infected person.

Most people have been affected with the type 1 virus by the age of 20. In addition to oral and genital lesions, the virus can also cause an infection of the eye involving the eyelid, conjunctiva, and cornea. A finger infection, called herpetic whitlow, affects health care providers (because of exposure to lung and mouth secretions during procedures) and young children. The herpes virus can also infect the fetus and cause congenital abnormalities. Herpes virus type 2 can be transmitted to a newborn during vaginal delivery if the mother is actively infected at the time of delivery. Encephalitis (rarely) may occur as a result of herpes infection.

Infection occurs after exposure to the virus through a break in the skin, or through mucus membranes. There is strong evidence that the virus may be transmitted even when symptoms are not present. The virus spreads to nerve cells within the body, and then to other mucosal skin surfaces. The virus remains dormant in the body after an active infection and recurrences of the symptoms can take place at a later time. Recurrences may be precipitated by overexposure to sunlight, fever, stress, or certain foods and drugs.