Clinical Overview

Herpes zoster, also known as zoster and shingles, is caused by infection with the varicella zoster virus (VZV), the same virus that causes varicella (chickenpox). Primary infection with VZV causes varicella and once the illness resolves, the virus remains in the dorsal root ganglia. Reactivation of the virus results in a localized cutaneous rash called herpes zoster.

Most people typically have only one episode of herpes zoster in their lifetime; however, second and even third episodes are possible. The annual incidence of repeat episodes of herpes zoster is not known.

Clinical Features

Herpes zoster typically presents as a painful rash in one or two adjacent dermatomes, most commonly in a thoracic dermatome. Pain, itching, or tingling in the area where the rash develops is typical and may precede rash onset by days to weeks. Headache, photophobia, and malaise may also occur in the prodromal phase. The rash is usually localized to one or two dermatomes and does not cross the body’s midline. However, lesions may overlap adjacent dermatomes in 20% of cases.

Herpes zoster begins as an erythematous, maculopapular rash that develops into clusters of clear vesicles. New vesicles continue to form over 3–5 days and progressively crust over; healing occurs over 2–4 weeks. There may be permanent pigmentation changes and scarring on the skin. In rare cases, usually among immunocompromised persons, the rash may become generalized and appear similar to a varicella rash.

Complications

The most common complication of herpes zoster is postherpetic neuralgia (PHN), pain that persists in the area where the rash was present after the rash has resolved. The duration of pain after rash onset is often used to define the existence of PHN; however, that period of time has not been precisely defined. Some define it as any duration of pain after resolution of the rash, and others define it as duration of pain for more than 30 days or more than 6 months after rash onset. PHN can last for weeks or months and occasionally persists for many years. The incidence, duration, and severity of PHN increases with increasing age: it occurs rarely among persons under 40 years of age but occurs in up to 50% (and possibly more) of persons 60 years of age and older. The pain can be severe and debilitating.

Other complications of herpes zoster include ophthalmic involvement with acute or chronic ocular sequelae; bacterial superinfection of the lesions, usually due to Staphylococcus aureus and, less commonly, to group A beta hemolytic streptococcus; cranial and peripheral nerve palsies; and visceral involvement (e.g., meningoencephalitis, pneumonitis, hepatitis, acute retinal necrosis). Complications occur more frequently and with increased severity in persons with immunosuppressive medical conditions or those taking immunosuppressive medications. The herpes zoster rash in immunocompromised persons may also be more severe, and its duration prolonged. Immunocompromised persons are at increased risk of developing disseminated herpes zoster (defined as appearance of lesions outside the primary or adjacent dermatomes).

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Risk Factors

Anyone who has had varicella may develop herpes zoster, including children. However, herpes zoster most commonly occurs in older people, with the risk increasing sharply after 50 years of age. It is also more common in people who are immunocompromised or who are taking medications that suppress the immune system—specifically, cell-mediated immunity; they include people

• with cancer, especially leukemia and lymphoma.
• with human immunodeficiency virus.
• who have undergone bone marrow or solid organ (renal, cardiac, liver, and lung) transplantation.
• who are taking immunosuppressive medications, including steroids, chemotherapy, or transplant-related immunosuppressive medications.

It is thought that declining VZV-specific cell-mediated immunity is important in the development of herpes zoster. This declining immunity is related to age and/or immunosuppressive medical conditions and medications. A number of studies have found the incidence of herpes zoster to be higher in women than in men, but other studies have not found a difference(1,2); the reason for a possible variation is unknown.

Transmission

Herpes zoster lesions are infectious until they dry and crust over; however, the risk of transmission is low if the lesions are covered. Persons in the prodromal phase or who have PHN, but no longer have active lesions are not contagious. Transmission occurs via direct contact with an infected person, especially by direct contact with the rash. If the virus comes in contact with the conjunctiva or upper respiratory tract mucosa of a VZV-susceptible person, he or she will be at risk for developing varicella—not herpes zoster.

Persons with active lesions, including localized zoster, should avoid contact with susceptible persons at high risk for severe chickenpox in household and occupational settings until lesions are crusted. Susceptible persons include pregnant women who have never had chickenpox or varicella vaccine, all premature infants born to susceptible mothers, infants born at <28 weeks gestation or who weigh <1000 g, regardless of maternal immune response, and immunocompromised persons of all ages.

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Rates of Herpes Zoster

On the basis of data from the National Health and Nutrition Examination Survey (NHANES 1999-2004), it is estimated that 98% of adults 20–49 years of age in the United States have serologic evidence of VZV infection and are at risk for herpes zoster. The lifetime risk of developing herpes zoster is about 30% and each year there are an estimated one million cases of herpes zoster in the United States.

Herpes Zoster in Persons Who Received Varicella Vaccine

Currently available data suggest that children who have been vaccinated against varicella may still develop herpes zoster later in life, but they do so at lower rates than those who have been infected with wild-type VZV. In a study of children with leukemia, the risk of herpes zoster occurring in vaccine recipients was about one-third that in children who had a history of varicella disease.(3)

Data relating to the risk of herpes zoster in healthy children show a similar pattern of reduced risk in vaccine recipients, but these data are limited and do not distinguish between shingles resulting from the varicella vaccine virus and herpes zoster resulting from natural VZV infection as a result of varicella vaccine failure. Furthermore, since the number of older adults who have received varicella vaccine since it was licensed in 1995 is quite low, these data are only available for children, and children are generally at low risk for herpes zoster.

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