Herpes zoster overview

# Overview
Herpes zoster (or simply zoster), commonly known as shingles, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe. The initial infection with varicella zoster virus (VZV) causes the acute (short-lived) illness chickenpox, and generally occurs in children and young people. Once an episode of chickenpox has resolved, the virus is not eliminated from the body but can go on to cause shinglesan illness with very different symptomsoften many years after the initial infection.
Varicella zoster virus can become latent in the nerve cell bodies and less frequently in non-neuronal satellite cells of dorsal root, cranial nerve or autonomic ganglion, without causing any symptoms. In an immunocompromised individual, perhaps years or decades after a chickenpox infection, the virus may break out of nerve cell bodies and travel down nerve axons to cause viral infection of the skin in the region of the nerve. The virus may spread from one or more ganglia along nerves of an affected segment and infect the corresponding dermatome (an area of skin supplied by one spinal nerve) causing a painful rash. Although the rash usually heals within two to four weeks, some sufferers experience residual nerve pain for months or years, a condition called postherpetic neuralgia. Exactly how the virus remains latent in the body, and subsequently re-activates is not understood.
Throughout the world the incidence rate of herpes zoster every year ranges from 1.2 to 3.4 cases  per 1,000 healthy individuals, increasing to 3.911.8 per year per 1,000 individuals among those older than 65 years. Antiviral drug treatment can reduce the severity and duration of herpes zoster, if a seven to ten day course of these drugs is started within 72 hours of the appearance of the characteristic rash.   

# Historical Perspective
Herpes zoster has a long recorded history, although historical accounts fail to distinguish the blistering caused by VZV and those caused by smallpox, ergotism, and erysipelas. It was only in the late eighteenth century that William Heberden established a way to differentiate between herpes zoster and smallpox, and only in the late nineteenth century that herpes zoster was differentiated from erysipelas. The first indications that chickenpox and herpes zoster were caused by the same virus were noticed at the beginning of the 20th century. Physicians began to report that cases of herpes zoster were often followed by chickenpox in the younger people who lived with the shingles patients. The idea of an association between the two diseases gained strength when it was shown that lymph from a sufferer of herpes zoster could induce chickenpox in young volunteers. This was finally proved by the first isolation of the virus in cell cultures, by the Nobel laureate Thomas H. Weller in 1953.

# Pathophysiology
The causative agent for herpes zoster is varicella zoster virus (VZV), a double-stranded DNA virus related to the Herpes simplex virus group. Most people are infected with this virus as children, and suffer from an episode of chickenpox. The immune system eventually eliminates the virus from most locations, but it remains dormant (or latent) in the ganglia adjacent to the spinal cord (called the dorsal root ganglion) or the ganglion semilunare (ganglion Gasseri) in the base of the skull.

# Causes
Shingles can only arise in individuals who have been previously exposed to chickenpox (varicella zoster). After a person recovers from chickenpox, the virus stays in the body in a dormant (inactive) state. Herpes zoster is not caused by the same virus that causes genital herpes, a sexually transmitted disease.The disease arises from various events which depress the immune system, such as aging, severe emotional stress, severe illness, immunosuppression or long-term use of corticosteroids.  The cellular and immunological events that lead to reactivation are poorly understood. There have been recorded cases of outbreaks occurring due to unmanaged stress or other stresses to the skin such as pinching, biting or scratching of  more sensitive areas, such as nipples, ears, and underarms.

# Differentiation Herpes zoster from other Diseases
] of Herpes zoster

# Epidemiology and Demographics
Before introduction of varicella vaccine in the United States in 1995, varicella was endemic, with virtually all persons being infected by adulthood. Since implementation of the varicella vaccination program, incidence has declined in all age groups, with the greatest decline among children aged 1-4 years. Data from passive and active surveillance have indicated a decline in varicella cases of 70%-84% from 1995 through 2001 (1-3). The downward trend in varicella has continued in the United States through 2005 with an approximately 90% decline in incidence from 1995 in active surveillance sites with high vaccine coverage(CDC, unpublished data).

# Risk Factors
Shingels are developed in patients who were previously infected with VZV (through natural infection that caused varicella or varicella vaccination).All older adults in the United States are at risk for herpes zoster as approximately 99.5% of people born in the United States who are 40 years of age and older have had varicella. Common risk factors include increasing age, immunosupression and stress.

# Screening
There is no recommended screening guideline for herpes zoster.

# Natural History, Complications and Prognosis
The earliest symptoms (constituting the prodrome) of shingles include headache, sensitivity to light, fever, and malaise, all of which may be followed by itching, tingling, and pain within one to seven days.The rash and pain usually subside within 3 to 5 weeks. Many patients develop a painful condition called postherpetic neuralgia, which is often difficult to manage. Postherpetic neuralgia is most common complication of Herpes zoster.

# Diagnosis

## History
A detailed history must be taken regarding the onset of symptoms, distribution and morphologic features of rash, accompanying symptoms, such as fever and pruritus and history of previous chicken pox infection must be obtained.

## Physical Examination
The characteristic physical examination finding of herpes zoster is the maculopapular rash. The rash in typically unilateral and its distribution is confined to one or two adjacent dermatomes. As the rash crusts and heals in 7-10 days, a post-inflammatory hyperpigmentation of the skin may result. Other findings, such as cranial and peripheral nerves involvement depend on the location of the dorsal root ganglia involved.

## Laboratory Findings
Laboratory testing may be useful in cases with less typical clinical presentations, such as in immunosuppressed persons who may have disseminated Herpes zoster (defined as appearance of lesions outside the primary or adjacent dermatomes).

## Electrocardiogram
Herpes zoster infection can simulate chest pain of cardiac origin. These patients have normal electrocardiographic findings. However, in very rare instances, herpes zoster infection can have cardiac complications, such as myocarditis, endocarditis, pericarditis and others.

## Chest X-Ray
A chest x-ray may be done to rule out other causes of chest pain.

## Other Imaging  Findings
Imaging is not routinely done to diagnose herpes zoster infection. However, it may be used as part of the work-up of the several but rare complications of herpes zoster infection.

## Other Diagnostic Studies
There are no other diagnostic studies for herpes zoster infection.

# Treatment

## Medical Therapy
Several antiviral medicinesacyclovir, valacyclovir, and famciclovirare available to treat shingles. These medicines will help shorten the length and severity of the illness. But to be effective, they must be started as soon as possible after the rash appears. Thus, people who have or think they might have shingles should call their healthcare provider as soon as possible to discuss treatment options. Analgesics (pain medicine) may help relieve the pain caused by shingles. Wet compresses, calamine lotion, and colloidal oatmeal baths may help relieve some of the itching.

## Primary Prevention
The only way to reduce the risk of developing shingles and the long-term pain that can follow shingles is to get vaccinated.  A vaccine for shingles is licensed for persons aged 60 years and older.

## Secondary Prevention
Infection-control measures after exposure to herpes zoster depend on whether the patient with herpes zoster is immunocompetent or immunocompromised and on whether the rash is localized or disseminated. In all cases, standard infection-control precautions should be followed.

## Cost-Effectiveness of Therapy
A live vaccine for VZV exists, marketed as Zostavax. A systematic review by the Cochrane Library concluded that Zostavax can reduce the incidence of herpes zoster by almost 50%. A 2007 study found that the zoster vaccine is likely to be cost-effective in the U.S., projecting an annual savings of $82 to $103 million in healthcare costs with cost-effectiveness ratios ranging from $16,229 to $27,609 per quality-adjusted life year gained. In October 2007 the vaccine was officially recommended in the U.S. for healthy adults aged 60 and over.

## Future of Investigational Therapies