Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are two species of the herpes virus family, Herpesviridae, which cause infections in humans. Eight members of herpes virus infect humans to cause a variety of illnesses including cold sores, chickenpox or varicella, shingles or herpes zoster (VZV), cytomegalovirus (CMV), and various cancers, and can cause brain inflammation (encephalitis). All viruses in the herpes family produce life-long infections.
They are also called Human Herpes Virus 1 and 2 (HHV-1 and HHV-2) and are neurotropic and neuroinvasive viruses; they enter and hide in the human nervous system, accounting for their durability in the human body. HSV-1 is commonly associated with herpes outbreaks of the face known as cold sores or fever blisters, whereas HSV-2 is more often associated with genital herpes.
An infection by a herpes simplex virus is marked by watery blisters in the skin or mucous membranes of the mouth, lips or genitals. Lesions heal with a scab characteristic of herpetic disease. However, the infection is persistent and symptoms may recur periodically as outbreaks of sores near the site of original infection. After the initial, or primary, infection, HSV becomes latent in the cell bodies of nerves in the area. Some infected people experience sporadic episodes of viral reactivation, followed by transportation of the virus via the nerve’s axon to the skin, where virus replication and shedding occurs.
Herpes is contagious if the carrier is producing and shedding the virus. This is especially likely during an outbreak but possible at other times. There is no cure yet, but there are treatments which reduce the likelihood of viral shedding.
HSV is transmitted during close contact with an infected person who is shedding virus from the skin, in saliva or in secretions from the genitals. This horizontal transmission of the virus is more likely to occur when sores are present, although viral shedding, and therefore transmission, does occur in the absence of visible sores. In addition, vertical transmission of HSV may occur between mother and child 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, the infection can result in inflammation of the brain (encephalitis) that may cause brain damage. Transmission occurs when the infant passes through the birth canal, but the risk of infection is reduced 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 carries a low (≈1%) risk of developing aseptic meningitis.
Herpes viruses are known for their ability to establish lifelong, incurable infections. Treatment usually involves general-purpose antiviral drugs which reduce, but are unable to completely eliminate, the infection. Reducing the viral load can reduce the physical severity of outbreak-associated lesions and the amount of infected cells shed by the body, lowering the chance of transmission to others. Research has also shown that the virus’s growth is to a moderate degree proportional to the ratio of the amino acid arginine to the amino acid lysine in the diet of infected individuals. Research into a vaccine is ongoing.