Shingles Health Article

Definition

Shingles is infection by the varicella-zoster virus of the dorsal root ganglia of the spine. Equivalent terms for shingles are herpes zoster, zoster, zona, or acute posterior ganglionitis.

Description

Shingles is an infection of the central nervous system, in particular, the dorsal root ganglia of the spine, which migrates through sensory nerves to the skin. There it manifests (usually on the upper trunk) as painful, bumpy, fluid-filled eruptions or vesicles. Shingles may also cause nerve pain (neuralgia). The affected areas of skin are those supplied by sensory nerves radiating from the infected dorsal root ganglia. Sensory nerves from these ganglia serve non-overlapping, sharply bounded strips or areas of the skin called dermatomes. Because the left and right sides of the body are divided into separate sets of dermatomes, shingles lesions do not cross the midline of the body.

Demographics

The virus that causes shingles is usually contracted in childhood. It is the same virus that causes chicken pox, which is primarily a disease of childhood because it is highly contagious; that is, few individuals live to adulthood without contracting chicken pox. (This statement applies to the temperate zones of the world. For unknown reasons, chicken pox and shingles are less prevalent in tropical regions.) The virus that causes both chicken pox and shingles can, however, be contracted by an individual for the first time in adulthood. First infection, at whatever age it occurs, is called primary infection. Primary infection does not cause shingles; shingles arises from reactivation of virus introduced to the body by an earlier, primary infection.

Shingles arises in individuals who have already had chicken pox, and especially in people with weakened immune systems, such as the elderly or people receiving chemotherapy or bone marrow transplantation. Persons with AIDS are also vulnerable to shingles. Shingles incidence increases steadily with age. Among 10–19 year olds, the rate per 1,000 persons per year is only 1.38. In the 30–49 age range, it rises to 2.29 cases of shingles per 1,000 persons per year. By age 60–79, almost seven cases occur per 1,000 people per year, and this increases to 10 in the 80–89 age group.

Causes and symptoms

Shingles is caused by the varicella-zoster virus (VZV), also known as HHV-3. VZV is genetically similar to the herpes simplex viruses, the type of viruses that causes cold sores and genital herpes. Herpes simplex virus also takes up permanent residence in sensory nerve ganglia, but not in the dorsal root ganglia of the spine, as does VZV. In chicken pox, the virus is inhaled and begins replicating in the upper respiratory tract before spreading to the liver and other body systems.

Following primary infection, VZV remains as a symptomless infection in the dorsal root ganglia of the spinal cord. It may or may not become active again, that is, begin reproducing, later in life. Reactivation occurs more often in older people, probably as a result of decreased immune response with age. Reactivation may be symptomless, but usually causes shingles. Repeat episodes of shingles are rare (occurring in less than 4% of patients) because the immune system's response to VZV is boosted by a first shingles episode.

Chills, fever, malaise, gastrointestinal problems, and pain in the affected skin areas may precede appearance of skin eruptions by several days. Viral particles travel away from the spinal cord along the sensory nerves toward the skin, causing inflammation of those nerves, which may be painful. On the fourth or fifth day, skin vesicles begin to appear. The affected area is usually hypersensitive, and disabling pain (described as sharp, stabbing, or burning) may occur in the affected area. About the fifth day after appearing, the vesicles begin to crust or scab and the disease resolves within the next two weeks. There may be no visible aftereffects, although slight scarring from the vesicles may occur.

Especially in elderly patients, pain may persist for months or years after shingles has otherwise resolved. This pain, postherpetic neuralgia, is caused by damage to the dorsal root ganglia that renders them either spontaneously active (perceived as chronic pain) or hypersensitive to slight stimuli such as light touch.

VZV can become active in the cranial nerves as well as in the spinal ganglia. Involvement of branches of the trigeminal nerve (fifth cranial nerve) is most common. When the ophthalmic branch of the trigeminal nerve is involved, this condition is called herpes zoster ophthalmicus. It can cause swelling of the eyelid, pain, and other complications involving the eye. Herpes zoster ophthalmicus can also lead to weakness or partial paralysis (hemiparesis) on the opposite side of the body from the nerve affected, possibly by inducing irritation of the blood vessels in the brain. Infection of cranial nerves by reactivated VZV can also affect the hearing. When this occurs, it is usually associated with facial palsy and is known as Ramsay-Hunt syndrome.

Large amounts of free virus (i.e., virus not held inside cells) is present in the fluid-filled vesicles or bumps that erupt on the skin during shingles. Thus, people who are not resistant to VZV are easily infected by contact with persons having an outbreak of shingles. A particular strain of VZV can remain latent for decades and then reappear as a new epidemic.