Shingles, also known as herpes zoster or zona,[6] is a viral disease characterized by a painful skin rash with blisters in a localized area.

[1][9] The rash usually heals within two to four weeks,[2] but some people develop ongoing nerve pain which can last for months or years, a condition called postherpetic neuralgia (PHN).

[1] If shingles develops, antiviral medications such as aciclovir can reduce the severity and duration of disease if started within 72 hours of the appearance of the rash.

[9][20] These symptoms are commonly followed by sensations of burning pain, itching, hyperesthesia (oversensitivity), or paresthesia ("pins and needles": tingling, pricking, or numbness).

In some people, symptoms may include conjunctivitis, keratitis, uveitis, and optic nerve palsies that can sometimes cause chronic ocular inflammation, loss of vision, and debilitating pain.

[31] In the mouth, shingles appears initially as 1–4 mm opaque blisters (vesicles),[30] which break down quickly to leave ulcers that heal within 10–14 days.

[40] Due to difficulties in studying VZV reactivation directly in humans (leading to reliance on small-animal models), its latency is less well understood than that of the herpes simplex virus.

Why this suppression sometimes fails is poorly understood,[44] but shingles is more likely to occur in people whose immune systems are impaired due to aging, immunosuppressive therapy, psychological stress, or other factors.

The short- and long-term pain caused by shingles outbreaks originates from inflammation of affected nerves due to the widespread growth of the virus in those areas.

[47] As with chickenpox and other forms of alpha-herpesvirus infection, direct contact with an active rash can spread the virus to a person who lacks immunity to it.

[49][50] When the rash is absent (early or late in the disease, or in the case of zoster sine herpete), shingles can be difficult to diagnose.

The most popular test detects VZV-specific IgM antibody in blood; this appears only during chickenpox or shingles and not while the virus is dormant.

[52] In larger laboratories, lymph collected from a blister is tested by polymerase chain reaction (PCR) for VZV DNA, or examined with an electron microscope for virus particles.

[medical citation needed] A trial comparing aciclovir with its prodrug, valaciclovir, demonstrated similar efficacies in treating this form of the disease.

In some people, shingles can reactivate presenting as zoster sine herpete: pain radiating along the path of a single spinal nerve (a dermatomal distribution), but without an accompanying rash.

This condition may involve complications that affect several levels of the nervous system and cause many cranial neuropathies, polyneuritis, myelitis, or aseptic meningitis.

[75] Although shingles typically resolves within 3–5 weeks, certain complications may arise: Varicella zoster virus (VZV) has a high level of infectivity and has a worldwide prevalence.

[9][79] This relationship with age has been demonstrated in many countries,[9][79][80][81][82][83] and is attributed to the fact that cellular immunity declines as people grow older.

When routine chickenpox vaccination was introduced in the United States, there was concern that, because older adults would no longer receive this natural periodic boost, there would be an increase in the incidence of shingles.

Multiple studies and surveillance data, at least when viewed superficially, demonstrate no consistent trends in incidence in the U.S. since the chickenpox vaccination program began in 1995.

[92] However, upon closer inspection, the two studies that showed no increase in shingles incidence were conducted among populations where varicella vaccination was not as yet widespread in the community.

[93][94] A later study by Patel et al. concluded that since the introduction of the chickenpox vaccine, hospitalization costs for complications of shingles increased by more than $700 million annually for those over age 60.

In 1831 Richard Bright hypothesized that the disease arose from the dorsal root ganglion, and an 1861 paper by Felix von Bärensprung confirmed this.

The idea of an association between the two diseases gained strength when it was shown that lymph from a person with shingles could induce chickenpox in young volunteers.

Further studies during the 1950s on immunosuppressed individuals showed that the disease was not as benign as once thought, and the search for various therapeutic and preventive measures began.

[110] The family name of all the herpesviruses derives from the Greek word έρπης herpēs,[111] from έρπω herpein ("to creep"),[112][113][114] referring to the latent, recurring infections typical of this group of viruses.

[120] Classic textbook descriptions state that VZV reactivation in the CNS is restricted to immunocompromised individuals and the elderly; however, studies have found that most participants are immunocompetent, and younger than 60 years old.

[120] The frequency of CNS infections presented at the emergency room of a community hospital is not negligible, so a means of diagnosing cases is needed.

For example, in the past, clinicians believed that encephalitis was caused by herpes simplex and that people always died or developed serious long-term function problems.

DNA techniques have made it possible to diagnose "mild" cases, caused by VZV or HSV, in which the symptoms include fever, headache, and altered mental status.