Shingles (herpes zoster) is infection that results from reactivation of the varicella-zoster virus, the virus that causes chickenpox.
Chickenpox and shingles are caused by the varicella-zoster virus (another member of the herpesvirus family). Chickenpox is the initial infection (see see Chickenpox), and shingles is a reactivation of the virus, usually years later. During chickenpox, the virus spreads in the bloodstream and infects collections of nerve cells (ganglia) of the spinal or cranial nerves. The virus remains in the ganglia in a dormant (latent) state. The virus may never cause symptoms again, or it may reactivate many years later. When it reactivates, the virus travels down the nerve fibers to the skin, where it creates painful sores resembling those of chickenpox. This outbreak of sores (shingles) almost always appears on a strip of the skin over the infected nerve fibers and only on one side of the body. This strip of skin, the area supplied by nerve fibers from a single spinal nerve, is called a dermatome (see Fig. 2: Dermatomes). Adjacent dermatomes may also be infected.
Unlike HSV infections, which can recur many times, there is usually only one outbreak of shingles in a person's lifetime. However, people with a weakened immune system may have shingles more than once. They may also have unusual sores, sores on many dermatomes, or sores on both sides of the body.
Shingles may develop at any age but is most common after age 50. Most often, the reason for reactivation is unknown. However, reactivation sometimes occurs when the immune system is weakened by another disorder, such as AIDS or Hodgkin lymphoma, or by use of drugs that suppress the immune system (for example to prevent rejection of a transplanted organ). The occurrence of shingles does not usually mean that the person has another serious disease.
Symptoms and Complications
During the 2 or 3 days before shingles develops, some people feel ill and have chills, a fever, nausea, diarrhea, or difficulty urinating. Others experience pain, a tingling sensation, or itching in a strip of skin on one side of the body. Clusters of small, fluid-filled blisters surrounded by a small red area then develop on this strip of skin. The blisters occur only on the limited area of skin supplied by the infected nerve fibers. Most often, blisters appear on the trunk, usually on only one side. However, a few blisters may also appear elsewhere. The affected area is usually sensitive to any stimulus, including light touch, and may be very painful. Symptoms are usually less severe in children than in adults.
The blisters begin to dry and form a scab about 5 days after they appear. Until scabs appear, the blisters contain varicella-zoster virus, which, if spread to susceptible people, can cause chickenpox. Blisters that cover large areas of skin or persist for more than 2 weeks usually indicate that the immune system is not functioning normally.
The affected skin, especially in older people and in people with a weakened immune system, may become infected by bacteria. Scratching the blisters increases this risk. Bacterial infections increase the risk of scarring.
One episode of shingles gives most people lifelong immunity from further attacks. Fewer than 4% of people have more than one episode. Scarring or hyperpigmentation of the skin, which can be extensive, may occur, but most people recover without lasting effects. A few people, more commonly older people, continue to have chronic pain in the area (postherpetic neuralgia).
Involvement of the part of the facial nerve leading to the eye can be serious, and if it is not treated adequately, vision may be affected. The part of the facial nerve leading to the ear may also be affected, sometimes causing pain, partial paralysis of the face, and hearing loss.
People who suspect they have shingles should see a doctor right away because to be effective, treatment must be started early. Doctors ask them to precisely describe the location of the pain. Pain in a vague band on one side of the body suggests shingles. If characteristic blisters appear in the typical pattern (on a strip of skin representing a dermatome), the diagnosis is clear. Rarely, doctors take a sample from the blisters to be analyzed or do a skin biopsy to confirm the diagnosis.
Prevention and Treatment
Preventing chickenpox by vaccinating children with the varicella vaccine is recommended. Adults who are not immune should also be vaccinated. Vaccination is particularly important for such people if they have frequent contact with children, live or work in places where infections can be spread (including college dormitories, barracks, and institutions such as prisons and nursing homes), have close contact with people with immune system problems, or travel overseas. Adults are considered to be immune and not need vaccination if they have ever had chickenpox or shingles, if a laboratory test done on a blood sample shows they have immunity, or if they were born before 1980 (except for women who may become pregnant and for health care workers). The vaccine sometimes has side effects, which are usually minor. However, rarely, the vaccine itself causes a mild form of shingles. The vaccine should not be given during pregnancy or to people with a weakened immune system (for example, people who have leukemia).
Another vaccine, developed to prevent shingles, can be given to healthy people older than 60, regardless of whether they have had a history of shingles. This vaccine decreases the chance of getting shingles by one half and decreases the chance of getting postherpetic neuralgia by two thirds. If shingles develops in people who have been vaccinated, it is less severe than in those who have not been vaccinated.
Several antiviral drugs are effective in treating shingles. Oral antiviral drugs such as famciclovir, valacyclovir, and acyclovir are often given, particularly to older people and to people with a weakened immune system. The drugs should be started as soon as shingles is suspected, before blisters appear if possible. The drugs are likely to be ineffective if started more than 3 days after blisters appear. These drugs do not cure the disease, but they can help relieve and shorten the duration of symptoms. Some doctors recommend taking corticosteroids in addition, but it is not clear whether this approach helps. If an eye or ear is involved, the appropriate specialist (ophthalmologist or otolaryngologist) should be consulted.
Wet compresses are soothing, but pain-relieving drugs are often required. Nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen may be tried, but oral opioid analgesics are often necessary (see see Treatment of Pain). To prevent bacterial infections from developing, people with shingles should keep the affected skin clean and dry and should not scratch the blisters.
Last full review/revision November 2009 by Marguerite A. Urban, MD