Definition of Herpes simplex:

Herpes simplex is an infection that mainly affects the mouth or genital area.

Causes, incidence, and risk factors:

There are two different strains of herpes simplex viruses:

• Herpes simplex virus type 1 (HSV-1) is usually associated with infections of the lips, mouth, and face. It is the most common herpes simplex virus and most people develop it in childhood. HSV-1 often causes lesions inside the mouth, such as cold sores (fever blisters), or infection of the eye (especially the conjunctiva and cornea). It can also lead to infection of the lining of the brain (meningoencephalitis). It is transmitted by contact with infected saliva. By adulthood, up to 90% of people will have antibodies to HSV-1.
• Herpes simplex virus 2 (HSV-2) is sexually transmitted. Symptoms include genital ulcers or sores. In addition to oral and genital sores, the virus can also lead to complications such as infection of the lining of the brain and the brain itself (meningoencephalitis) in neonatal infants due to infection during birth. However, some people have HSV-2 but do not show symptoms. Up to 30% of U.S. adults have antibodies against HSV-2. Cross-infection of type 1 and 2 viruses may occur from oral-genital contact.

A finger infection, called herpetic whitlow, is another form of herpes. It usually affects health care providers who are exposed to saliva during procedures. Sometimes, young children also can get the disease.

The herpes virus can infect the fetus and cause abnormalities. A mother who is infected with herpes may transmit the virus to her newborn during vaginal delivery, especially if the mother has an active infection at the time of delivery.

It's possible for the virus to be transmitted even when there are no symptoms or visible sores.