The herpes simplex virus (HSV) (also known as cold sore, night fever, or fever blister) is a virus that manifests itself in two common viral infections, each marked by painful, watery blisters in the skin or mucous membranes (such as the mouth or lips) or on the genitals. The disease is contagious, particularly during an outbreak, and is incurable with present technology. An infection on the lips is commonly known as a "cold sore" or "fever blister". These are sometimes confused with canker sores or aphthous ulcers, which have a similar appearance; these appear inside the mouth and are not caused by the herpes simplex virus. When not symptomatic HSV lies dormant in the bodies of the nerve cells, growing up the axons to the skin during an outbreak. When the outbreak has passed, the virus 'dies back' along the nerve until it is only present in the nerve body. The dormancy of the virus within the nerve bodies contributes to the difficulty of treatment.
HSV is generally transmitted by direct contact of lips and/or genitals when the sores are present, or just before they appear (known as shedding). In addition, herpes may be transmitted during childbirth, which can be fatal to the infant. The immature immune system of the child is unable to defend against the virus and even if treated, infection can result in brain damage. Transmission occurs while passing through the birth canal and the risk of infection is minimal if there are no symptoms or exposed blisters during delivery. The first outbreak after exposure to HSV is commonly more severe than future outbreaks, as the body has not had a chance to produce antibodies; this first outbreak also carries the risk of developing meningitis.
Outbreaks are generally preceded by sensations of burning, itching or tingling before visible blistering occurs. Subclinical shedding can also occur at any time, resulting in transmission without symptoms.
