Herpes

Herpes simplex, commonly called herpes, is a viral infection caused by the herpes simplex virus. The infection is classified by the part of the body it affects, with oral herpes (causing cold sores or fever blisters on the face or mouth, or a sore throat) and genital herpes (affecting the genitalia, sometimes with minimal symptoms or with blisters that turn into small ulcers and heal in two to four weeks) being the two main types. Before blisters appear, tingling or shooting pains may occur. The condition cycles between active episodes and symptom-free periods; the first episode is often more severe, possibly involving fever, muscle pains, swollen lymph nodes, and headaches, and over time, episodes become less frequent and less severe.

Other forms include herpetic whitlow (on the fingers or thumb), herpes simplex keratitis (in the eye), herpesviral encephalitis (in the brain), and neonatal herpes (affecting any part of a newborn’s body). Two virus types exist: HSV-1, which more often causes oral infections, and HSV-2, which more often causes genital infections. Transmission occurs through direct contact with body fluids or lesions of an infected person, and it can happen even when no symptoms are present. Genital herpes is a sexually transmitted infection and can be passed to an infant during childbirth. After infection, the viruses travel along sensory nerves to nerve cell bodies, where they remain for life. Recurrence may be triggered by decreased immune function, stress, or sunlight exposure. Diagnosis is usually based on symptoms; swabs from active lesions can be tested via viral culture or PCR for viral DNA, while blood tests for IgG antibodies confirm past exposure but can give false negatives during the seroconversion window weeks after a new infection.

The most effective way to avoid genital infection is to avoid vaginal, oral, manual, and anal sex. Condom use reduces risk, and daily antiviral medication taken by an infected person can also lower transmission. No vaccine exists, and there is no cure once infected. Paracetamol (acetaminophen) and topical lidocaine can help with symptoms, while antiviral drugs like aciclovir or valaciclovir can reduce the severity of active episodes. Worldwide, 60% to 95% of adults have either HSV-1 or HSV-2. HSV-1 is usually acquired in childhood, and since there is no cure, infection rates increase with age. HSV-1 prevalence is 70% to 80% in low socioeconomic status populations and 40% to 60% in higher socioeconomic groups. As of 2003, an estimated 536 million people (16% of the global population) were infected with HSV-2, with higher rates among women and those in developing countries. Most people with HSV-2 do not know they are infected.

The name comes from Ancient Greek *herpēs*, meaning 'to creep,' referring to spreading blisters, not to latency. HSV infection can cause several distinct disorders, including orofacial herpes, genital herpes, herpetic whitlow, herpes keratitis (eye damage), and herpes encephalitis (brain damage). People with immature or suppressed immune systems—such as newborns, transplant recipients, or those with AIDS—are prone to severe complications. HSV infection has also been linked to cognitive deficits in bipolar disorder and Alzheimer’s disease, though this often depends on the person’s genetics. The immune system never removes HSV; after a primary infection, the virus enters nerves at the site, migrates to the neuron’s cell body, and becomes latent in the ganglion. The body produces antibodies to the specific HSV type, which can reduce the odds of later infection with that type at a different site. For HSV-1-infected individuals, seroconversion after an oral infection helps prevent additional HSV-1 infections like whitlow, genital herpes, or eye herpes. Prior HSV-1 seroconversion seems to reduce symptoms of a later HSV-2 infection, but HSV-2 can still be contracted. Many people with HSV-2 have no physical symptoms (asymptomatic or subclinical herpes), though infection can be fatal.

Neonatal herpes simplex, a rare but serious condition in infants, is usually caused by mother-to-newborn transmission of HSV-1 or -2. During immunodeficiency, herpes simplex can cause unusual skin lesions, including clean linear erosions in skin creases that look like knife cuts. Herpetic sycosis is a recurrent or initial infection affecting hair follicles. Eczema herpeticum occurs in patients with chronic atopic dermatitis, where the virus spreads throughout eczematous areas. Herpetic keratoconjunctivitis, a primary infection, typically presents as swelling of the conjunctiva and eyelids (blepharoconjunctivitis), accompanied by small white spots.