HSV-1 is a highly contagious infection, widespread and endemic throughout the world. Infection of HSV-1 occurs in most cases in childhood, and the infection remains for life. The vast majority of HSV-1 infections develop oral herpes (infection in or around the mouth, sometimes called orolabial or orofacial herpes), but in some cases HSV-1 also causes genital herpes (infection in the genital or anal region).
Scale of the problem
It is estimated that in 2016 about 3.7 billion people under the age of 50, or 67% of the world’s population, were infected with HSV-1 (with herpes in the mouth or genital area). The highest prevalence rates were estimated to be in Africa (88%) and the lowest in the Americas (45%).
Most HSV-1 infections were oral infections. It is estimated that between 122 million and 192 million people aged 15-49 years worldwide had HSV-1 genital infections in 2016, but the prevalence varied significantly across regions. It is estimated that the largest number of cases of HSV-1 infection occurred in the Americas, the European Region and the Western Pacific Region, where HSV-1 infection continues into adulthood.
Signs and symptoms
Herpetic oral infection tends to be asymptomatic, and most people infected with HSV-1 are not aware that they are infected. Oral herpes symptoms include painful vesicles or open lesions, called ulcers, in or around the mouth. Lesions on the lips are usually called ‘fever’. Before the lesions occur, infected persons often feel a tingling, itchy or burning sensation in the mouth area. After the initial infection, bubbles or ulcers may recur periodically. The frequency of their occurrence varies from person to person.
Genital herpes caused by HSV-1 may be asymptomatic or with mild symptoms that remain unrecognized. In cases where symptoms do occur, genital herpes is characterized by the appearance of one or more vesicles or ulcers in the genital or anal area. After the initial episode of genital herpes, which can be severe, symptoms may reappear. However, genital herpes caused by herpes simplex virus type 2 (HSV-2; see below) is usually not repeated frequently.
Transmission of infection
HSV-1 is transmitted mainly by oral contact and causes herpetic infection of the oral cavity through contact with HSV-1 in the lesions, saliva and surfaces in or around the mouth. However, due to oral genital contact, HSV-1 may also enter the genital area and cause genital herpes.
HSV-1 may be transmitted through the oral surface or through skin that looks normal and shows no symptoms. However, the greatest risk of transmission exists when there are active lesions.
In individuals who already have herpetic oral infection, subsequent infection of the HSV-1 genital area is unlikely.
In rare cases, infection caused by GBP-1 may be transmitted from a mother with GBP-1 genitalia to her child at birth and lead to neonatal herpes.
Severe illness. In persons with a weak immune system, such as those with advanced HIV infection, HSV-1 can lead to more severe symptoms and more frequent relapses. In rare cases, infection caused by HSV-1 may also lead to more severe complications, such as encephalitis (brain infection) or keratitis (eye infection).
The development of neonatal herpes may occur when a newborn baby comes into contact with HSV in the genital tract during childbirth. Neonatal herpes is rarely developed, estimated at 10 out of 100,000 births worldwide, but this severe condition can lead to persistent neurological disability or death. In women who have experienced genital herpes before pregnancy, the risk of transmitting HSV to their children is extremely low. The highest risk of neonatal herpes occurs when a woman first becomes infected with HSV in late pregnancy, partly because the highest levels of HSV concentration in the genital tract are observed in the early stages of infection.
The reappearance of oral herpes symptoms can cause discomfort and lead to some social stigmatization and psychological stress. In genital herpes, these factors can have a significant adverse effect on quality of life and sexual relationships. Over time, however, most people with some form of herpes will adapt to life with infection.