Herpes simplex virus type 1
| Herpes simplex virus | |
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| TEM micrograph of a herpes simplex virus | |
| Virus classification | |
| Group: | Group I (dsDNA) |
| Order: | Herpesvirales |
| Family: | Herpesviridae |
| Subfamily: | Alphaherpesvirinae |
| Genus: | Simplexvirus |
| Species | |
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Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known as human herpesvirus 1 and 2 (HHV-1 and HHV-2), are two members of the herpesvirus family, Herpesviridae, that infect humans. Both HSV-1 (which produces most cold sores) and HSV-2 (which produces most genital herpes) are ubiquitous and contagious. They can be spread when an infected person is producing and shedding the virus.
In simple terms, herpes simplex 1 is most commonly known as a "cold sore", while herpes simplex 2 is the one known by the public as "herpes", or "genital herpes". According to the World Health Organization 67% of the world population under the age of 50 have HSV-1.
Symptoms of herpes simplex virus infection include watery blisters in the skin or mucous membranes of the mouth, lips, nose or genitals. Lesions heal with a scab characteristic of herpetic disease. Sometimes, the viruses cause very mild or atypical symptoms during outbreaks. However, they can also cause more troublesome forms of herpes simplex. As neurotropic and neuroinvasive viruses, HSV-1 and -2 persist in the body by becoming latent and hiding from the immune system in the cell bodies of neurons. After the initial or primary infection, some infected people experience episodes of viral reactivation or outbreaks. In an outbreak, the virus in a nerve cell becomes active and is transported via the neuron's axon to the skin, where virus replication and shedding occur and cause new sores. It is one of the most common sexually transmitted infections.
HSV-1 and -2 are transmitted by contact with an infected person who has reactivations of the virus. Herpes simplex virus (HSV)-2 is periodically shed in the human genital tract, most often asymptomatically. Most sexual transmissions occur during periods of asymptomatic shedding. Asymptomatic reactivation means that the virus causes atypical, subtle or hard to notice symptoms that are not identified as an active herpes infection. It is therefore possible to acquire the virus even if no active HSV blisters or sores are present. In one study, daily genital swab samples found HSV-2 at a median of 12–28% of days among those who have had an outbreak, and 10% of days among those suffering from asymptomatic infection, with many of these episodes occurring without visible outbreak ("subclinical shedding").
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