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Herpes simplex virus

January 2016


Key facts

  • The herpes simplex virus, or herpes, is categorized into 2 types: herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2).
  • HSV-1 is mainly transmitted by oral-to-oral contact to cause oral herpes (which can include symptoms known as “cold sores”), but can also cause genital herpes.
  • HSV-2 is a sexually transmitted infection that causes genital herpes.
  • Both HSV-1 and HSV-2 infections are lifelong.
  • An estimated 3.7 billion people under age 50 (67%) have HSV-1 infection globally.
  • An estimated 417 million people aged 15-49 (11%) worldwide have HSV-2 infection.
  • Symptoms of herpes include painful blisters or ulcers at the site of infection.
  • Herpes infections are most contagious when symptoms are present but can still be transmitted to others in the absence of symptoms.
  • Infection with HSV-2 increases the risk of acquiring and transmitting HIV infection.

Introduction

Infection with the herpes simplex virus, commonly known as herpes, can be due to either herpes simplex virus type 1 (HSV-1) or herpes simplex virus type 2 (HSV-2). HSV-1 is mainly transmitted by oral to oral contact to cause infection in or around the mouth (oral herpes). HSV-2 is almost exclusively sexually transmitted, causing infection in the genital or anal area (genital herpes). However, HSV-1 can also be transmitted to the genital area through oral-genital contact to cause genital herpes.

Both oral herpes infections and genital herpes infections are mostly asymptomatic but can cause mild symptoms or painful blisters or ulcers at the site of infection.

Herpes simplex virus type 1 (HSV-1)

HSV-1 is a highly contagious infection, which is common and endemic throughout the world. Most HSV-1 infections are acquired during childhood, and infection is lifelong. The vast majority of HSV-1 infections are oral herpes (infections in or around the mouth, sometimes called orolabial, oral-labial or oral-facial herpes), but a proportion of HSV-1 infections are genital herpes (infections in the genital or anal area).

Scope of the problem

In 2012, an estimated 3.7 billion people under the age of 50, or 67% of the population, had HSV-1 infection. Estimated prevalence of the infection was highest in Africa (87%) and lowest in the Americas (40-50%).

With respect to genital HSV-1 infection, 140 million people aged 15-49-years were estimated to have genital HSV-1 infection worldwide in 2012, but prevalence varied substantially by region. Most genital HSV-1 infections are estimated to occur in the Americas, Europe and Western Pacific, where HSV-1 continues to be acquired well into adulthood. In other regions, for example in Africa, most HSV-1 infections are acquired in childhood, before the age of sexual debut.

Signs and symptoms

Oral herpes infection is mostly asymptomatic, and the majority of people with HSV-1 infection are unaware they are infected. Symptoms of oral herpes include painful blisters or open sores called ulcers in or around the mouth. Sores on the lips are commonly referred to as “cold sores.” Infected persons will often experience a tingling, itching or burning sensation around their mouth, before the appearance of sores. After initial infection, the blisters or ulcers can periodically recur. The frequency of recurrences varies from person to person.

Genital herpes caused by HSV-1 can be asymptomatic or can have mild symptoms that go unrecognized. When symptoms do occur, genital herpes is characterised by 1 or more genital or anal blisters or ulcers. After an initial genital herpes episode, which may be severe, symptoms may recur, but genital herpes caused by HSV-1 often does not recur frequently.

Transmission

HSV-1 is mainly transmitted by oral-to-oral contact to cause oral herpes infection, via contact with the HSV-1 virus in sores, saliva, and surfaces in or around the mouth. However, HSV-1 can also be transmitted to the genital area through oral-genital contact to cause genital herpes.

HSV-1 can be transmitted from oral or skin surfaces that appear normal and when there are no symptoms present. However, the greatest risk of transmission is when there are active sores.

Individuals who already have HSV-1 oral herpes infection are unlikely to be subsequently infected with HSV-1 in the genital area.

In rare circumstances, HSV-1 infection can be transmitted from a mother with genital HSV-1 infection to her infant during delivery.

Possible complications

Severe disease

In immunocompromised people, such as those with advanced HIV infection, HSV-1 can have more severe symptoms and more frequent recurrences. Rarely, HSV-1 infection can also lead to more severe complications such as encephalitis or keratitis (eye infection).

Neonatal herpes

Neonatal herpes is a rare, but sometimes fatal, condition that can occur when an infant is exposed to HSV in the genital tract during delivery. The risk for neonatal herpes is greatest when a mother acquires HSV infection for the first time in late pregnancy. Women who have genital herpes before they become pregnant are at very low risk of transmitting HSV to their infants.

Psychosocial impact

Recurrent symptoms of oral herpes may be uncomfortable and can lead to some social stigma and psychological distress. With genital herpes, these factors can have an important impact on quality of life and sexual relationships. However, in time, most people with either kind of herpes adjust to living with the infection.

Treatment

Antiviral medications, such as acyclovir, famciclovir, and valacyclovir, are the most effective medications available for people infected with HSV. These can help to reduce the severity and frequency of symptoms, but cannot cure the infection.

Prevention

HSV-1 is most contagious during an outbreak of symptomatic oral herpes, but can also be transmitted when no symptoms are felt or visible. People with active symptoms of oral herpes should avoid oral contact with others and sharing objects that have contact with saliva. They should also abstain from oral sex, to avoid transmitting herpes to the genitals of a sexual partner. Individuals with symptoms of genital herpes should abstain from sexual activity whilst experiencing any of the symptoms.

People who already have HSV-1 infection are not at risk of getting it again, but they are still at risk of acquiring herpes simplex virus type 2 (HSV-2) genital infection (see below).

The consistent and correct use of condoms can help to prevent the spread of genital herpes. However, condoms can only reduce the risk of infection, as outbreaks of genital herpes can occur in areas not covered by a condom.

Pregnant women with symptoms of genital herpes should inform their health care providers. Prevention of a new genital herpes infection is particularly important for women in late pregnancy, as this is when the risk for neonatal herpes is greatest.

Additional research is underway to develop more effective prevention methods against HSV infection, such as vaccines. Several candidate HSV vaccines are currently being studied.

Herpes simplex virus type 2 (HSV-2)

HSV-2 infection is widespread throughout the world and is almost exclusively sexually transmitted, causing genital herpes. HSV-2 is the main cause of genital herpes, which can also be caused by herpes simplex virus type 1 (HSV-1). Infection with HSV-2 is lifelong and incurable.

Scope of the problem

Genital herpes caused by HSV-2 is a global issue, and an estimated 417 million people worldwide were living with the infection in 2012. Prevalence of HSV-2 infection was estimated to be highest in Africa (31.5%), followed by the Americas (14.4%). It was also shown to increase with age, though the highest numbers of people newly-infected were adolescents.

More women are infected with HSV-2 than men; in 2012 it was estimated that 267 million women and 150 million men were living with the infection. This is because sexual transmission of HSV is more efficient from men to women than from women to men.

Signs and symptoms

Genital herpes infections often have no symptoms, or mild symptoms that go unrecognised. Most infected people are unaware that they have the infection. Typically, about 10-20% of people with HSV-2 infection report a prior diagnosis of genital herpes.

When symptoms do occur, genital herpes is characterised by one or more genital or anal blisters or open sores called ulcers. In addition to genital ulcers, symptoms of new genital herpes infections often include fever, body aches, and swollen lymph nodes.

After an initial genital herpes infection with HSV-2, recurrent symptoms are common but often less severe than the first outbreak. The frequency of outbreaks tends to decrease over time. People infected with HSV-2 may experience sensations of mild tingling or shooting pain in the legs, hips, and buttocks before the occurrence of genital ulcers.

Transmission

HSV-2 is mainly transmitted during sex, through contact with genital surfaces, skin, sores or fluids of someone infected with the virus. HSV-2 can be transmitted from skin in the genital or anal area that looks normal and is often transmitted in the absence of symptoms.

In rare circumstances, HSV-2 infection can be transmitted from a mother to her infant during delivery.

Possible complications

HSV-2 and HIV

HSV-2 and HIV have been shown to influence each other. HSV-2 infection increases the risk of acquiring a new HIV infection by approximately three-fold. In addition, people with both HIV and HSV-2 infection are more likely to spread HIV to others. HSV-2 is amongst the most common infections in people living with HIV, occurring in 60-90% of HIV-infected persons.

Infection with HSV-2 in people living with HIV (and other immunocompromised individuals) often has a more severe presentation and more frequent recurrences. In advanced HIV disease, HSV-2 can lead to more serious, but rare, complications such as meningoencephalitis, esophagitis, hepatitis, pneumonitis, retinal necrosis, or disseminated infection.

Neonatal herpes

Neonatal herpes is a rare but sometimes fatal condition that can occur when an infant is exposed to HSV in the genital tract during delivery. The risk for neonatal herpes is greatest when a mother acquires HSV infection for the first time in late pregnancy. Women who have genital herpes before they become pregnant are at very low risk of transmitting HSV to their infants.

Psychosocial impact

Recurrent symptoms of genital herpes may be painful and the infection can lead to social stigma and psychological distress. These factors can have an important impact on quality of life and sexual relationships. However, in time, most people with herpes adjust to living with the infection.

Treatment

Antivirals, such as acyclovir, famciclovir, and valacyclovir are the most effective medications available for people infected with HSV. These can help to reduce the severity and frequency of symptoms, but cannot cure the infection.

Prevention

Individuals with genital HSV infection should abstain from sexual activity whilst experiencing symptoms of genital herpes. HSV-2 is most contagious during an outbreak of sores, but can also be transmitted when no symptoms are felt or visible.

The consistent and correct use of condoms can help reduce the risk of spreading genital herpes. However, condoms only provide partial protection, as HSV can be found in areas not covered by a condom. Medical male circumcision can provide men life-long partial protection against HSV-2, in addition to HIV and human papillomavirus (HPV).

Pregnant women with symptoms of genital herpes should inform their health care providers.

Additional research is underway to develop more effective prevention methods against HSV infection, such as vaccines or topical microbicides (compounds which can be applied inside the vagina or rectum to protect against sexually transmitted infections).

WHO response to Herpes (HSV-1 and HSV-2)

WHO and partners are working to accelerate research to develop new strategies for prevention and control of genital and neonatal HSV-1 and HSV-2 infections. Such research includes the development of HSV vaccines and topical microbicides. Several candidate vaccines and microbicides are currently being studied.

New estimates of the global numbers of HSV-1 infections and HSV-2 infections for 2012 have been released. New global estimates of neonatal herpes will be released in 2016.

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