Infection with HSV, 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 transmitted through genital-to-genital contact during sex, causing infection in the genital or anal area (genital herpes).
Herpes Simplex Virus Type 1 Epidemiology
Herpes simplex virus type 1 is a highly contagious infection, that is common and endemic throughout the world. The virus is predominantly acquired and transmitted orally leading to a lifelong infection. Infection with HSV-1 is the underlying cause of multiple diseases, though the most common clinical manifestation is that of oral herpes. HSV-1 acquisition usually occurs in childhood, well before sexual debut, where proximity to parents and other family members, as well as to peers, increases the likelihood of exposure and transmission.
Mounting evidence from Western countries, Asia, and Latin America and the Caribbean suggests that HSV-1 is increasingly acquired genitally, and less so orally. Indeed, in several countries, HSV-1 is already the primary cause of genital herpes.
In 2016, an estimated 3.7 billion people under the age of 50, or 67% of the population, had HSV-1 infection (oral or genital). Estimated prevalence of the infection was highest in Africa (88%) and lowest in the Americas (45%).
With respect to genital HSV-1 infection, between 122 million to 192 million people aged 15-49-years were estimated to have genital HSV-1 infection worldwide in 2016, 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.
Signs and Symptoms
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).
Both oral herpes infections and genital herpes infections are mostly asymptomatic or unrecognized but can cause symptoms of painful blisters or ulcers at the site of infection, ranging from mild to severe.
Most 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.” After initial infection, the blisters or ulcers can periodically recur. The frequency of recurrences varies from person to person.
Primary herpes is usually more severe than recurrent herpes. Both can cause painful blisters or ulcers on the lips or inside the mouth, but they may also cause similar lesions on other areas of the body, such as the face, hands, or genitals.
Typically, 1–2 days before an outbreak, the skin where the lesions occur will have a burning or tingling sensation. The child may also develop fever, swollen lymph nodes in the neck, irritability, poor appetite, and difficulty sleeping, especially with primary herpes.
Genital herpes caused by HSV-1 can be asymptomatic or can have mild symptoms that go unrecognized. When symptoms do occur, genital herpes is characterized by 1 one or more genital or anal blisters or ulcers. After an initial genital herpes episode, which can be severe, symptoms may recur. However, genital herpes caused by HSV-1 typically does not recur frequently, unlike genital herpes caused by HSV-2.
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.
Infants can also become infected with HSV through direct skin-to-skin contact with someone who has an active lesion. For instance: kissing a child when you have an active lesion, changing a diaper if there is a lesion on the hand or breastfeeding with a lesion on the breast.
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. Inpiduals 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 to cause neonatal herpes. However, HSV-1 can also be transmitted to the genital area through oral-genital contact to cause genital herpes.
Possible Complications
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 (brain infection) or keratitis (eye infection).
Neonatal Herpes
Neonatal herpes can occur when an infant is exposed to HSV (HSV-1 or HSV-2) in the genital tract during delivery. Transplacental transmission of virus and hospital-acquired spread from one neonate to another by hospital personnel or family may account for some cases. Neonatal herpes is rare, occurring in an estimated 10 out of every 100,000 births globally, but is a serious condition that can lead to lasting neurologic disability or death. Neonatal herpes simplex virus (HSV) infection has high mortality and significant morbidity.HSV-2 causes more cases than HSV-1.
Manifestations generally occur between the 1st and 3rd weeks of life but rarely may not appear until as late as the 4th week. Neonates may present with local or disseminated disease. Skin vesicles are common with either type, occurring in about 70% overall. Neonates with no skin vesicles usually present with localized central nervous system (CNS) disease. In neonates with isolated skin or mucosal disease, progressive or more serious forms of the disease frequently follow within 7 to 10 days if left untreated.
Neonates with localized disease can be pided into 2 groups. One group has encephalitis manifested by neurologic findings, with or without concomitant involvement of the skin, eyes, and mouth. The other group has only skin, eye, and mouth involvement and no evidence of CNS or organ disease.
Neonates with disseminated disease and visceral organ involvement have hepatitis, pneumonitis, disseminated intravascular coagulation, or a combination, with or without encephalitis or skin disease. Other signs, which can occur singly or in combination, include temperature instability, lethargy, hypotonia, respiratory distress, apnea, and seizures.
Women who have genital herpes before they become pregnant are at very low risk of transmitting HSV to their infants. The risk for neonatal herpes is greatest when a mother acquires HSV infection for the first time in late pregnancy, in part because the levels of HSV in the genital tract are highest early in 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. Inpiduals 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 HSV-2 genital infection.
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. Preventing the acquisition 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.
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