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Herpes simplex virus 1 (HSV1)

Herpes simplex virus (HSV) type 1 is a microorganism associated with the occurrence of cold sores on the face, lips, and mouth, hence, it causes mouth (oral) herpes. Nevertheless, HSV1 can also be the cause of genital herpes, although unusual.


It is estimated that about two-thirds of the population is infected with HSV type 1 and the majority of people are completely asymptomatic. When it still causes symptomatic disease typically it manifests with mouth and lip lesions known as cold sores, skin rash, and rash in the genital area. Sometimes the virus affects the eyes leading to herpetic keratitis and rarely serious brain infection or diseases in newborn babies.   

HSV-1 belongs to the alpha herpesvirus group. The virus contains an internal core with a linear double-stranded DNA which is surrounded by the capsid and a lipid envelope with viral glycoproteins on the surface.

Infection spread

HSV-1 infection is acquired more often and earlier compared to HSV-2. It is suggested that up to 90% of adults have antibodies to HSV-1 by 50. The prevalence of antibodies to HSV-1 increases with age and correlates with socioeconomic status, thus it is more prevalent in low- and middle-income countries.

HSV-1 is transmitted by oral-to-oral contact and exposure to infected saliva and mucous, it means that a person is getting infected while kissing or using the cutlery/dishes used by a person with active infection. More rarely someone without any symptoms may also infect others. Oral-to-genital and genital-to-genital transmission may also occur. The spread of HSV-1 infection from oral secretions to other skin areas is a possible hazard to some professionals such as dentists. Wrestlers are also at risk of contracting HSV-1 infection almost anywhere in the body.

Newborn babies acquire infection from their mothers during the delivery as they pass through the birth canal, typically if the mother has herpetic lesions, although this can happen even if there are no signs of infection.


After contracting the infection, the disease develops within 2-12 days with an average incubation period of HSV-1 is 4 days. Primary HSV-1 infection typically starts with inflammation of the gingiva, mouth mucosa, and throat (pharyngitis). These symptoms are more common in children at the age of 1 to 3 years and adults rarely experience them. The disease starts with a fever lasting for 2-7 days, sore throat, malaise, itching, burning sensations, muscle pain, inability to eat, irritability, enlargement of the neck glands, and swelling of the mouth mucosa. Tingling and pain may precede the occurrence of sores.

The vesicular rash caused by HSV appears like small blisters filled with fluid and may distribute on the hard and soft palate, tongue, gingiva, and around the lips. These lesions, also known as fever blisters or cold sores tend to rupture, leaving grey-white ulcers. In general, the disease lasts from 3 up to 21 days and the ulcers heal without leaving a scar.

Herpes labialis

HSV-1 may reactivate from time to time usually in the form of herpes labialis – cold sores on the rim of the mouth. Pain, burning, tingling, or itching sensations precede the development of cold sores. Within 24-48 hours afterward, the painful vesicles appear, typically on the border of the lip. From 3 to 4 days later the vesicles crust and after 8-10 days the lesions disappear.

Herpetic whitlow

HSV-1 infection of the finger is known as herpetic whitlow. It occurs when the broken skin of the hand is exposed to the virus. An infected finger swells and becomes reddish quickly, it is tender and painful to touch. Vesicles or pustular lesions are detected on the fingertip.

Herpes gladiatorum

Herpes gladiatorum (also known as mat herpes) is common for wrestlers and other sportsmen involved in high-contact sports. This type of HSV 1 infection develops due to the traumas of the mucosa and the skin as the virus penetrates through the injured epithelium. It may affect almost every part of the body.

Herpetic encephalitis

Herpetic infection can cause brain inflammation in individuals of any age group. This manifests with fever, fits, confusion, and headaches. Other symptoms may include weakness of certain muscles (paresis and paralysis), swallowing difficulties, and speech impairment.


The diagnosis is made based on clinical features mainly. Laboratory tests to detect the viral DNA via polymerase chain reaction (PCR) in the specimens taken from the affected skin are sometimes performed to confirm the disease’s cause. Viral cultures may also be helpful. The virus may also be found in mouth secretions from 7 to 10 days as well as in the stool.

Serologic testing to detect antibodies to herpes simplex virus type 1 is of limited use in clinical practice and is typically used to assess the prognosis of the disease. 


Antiviral medications such as acyclovir, valacyclovir, and famciclovir are commonly used for the treatment of herpes labialis, usually they are applied on the lesions in the form of cream. In case of severe infection or if the person has impaired immunity, acyclovir is administered as tablets at a dosage of 400 mg five times per day for 5 days. Valacyclovir may be used at a dosage of 2 g twice daily for 1 day with 12 hours in between the two doses.

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