Before the introduction of a vaccine to prevent chickenpox, the fever, blistering rash and severe itching associated with the disease were considered a childhood rite of passage. Although the symptoms generally faded quickly, the potential consequences for those who had this infection extend well into adulthood.
The virus responsible for chickenpox -- varicella-zoster -- doesn't disappear when the blisters heal. Small amounts of it remain in the body, lying inactive in clusters of nerve cells along the spinal cord.
Immunity acquired as a result of having chickenpox holds the virus in check, and most people experience no further problems with it. But in about 20% of people who have had chickenpox, the virus spontaneously reactivates later in life.
The reactivated virus begins to multiply in the nerve cells, then travels along the nerves to the skin's surface, where it causes a rash known as shingles. Unlike chickenpox, the rash doesn't usually involve the entire body. The small blisters appear only in the area in which the virus reactivated, typically a well-defined band of skin over one side of the chest, face or buttocks. The blisters crust over in about seven to 10 days, but generally take two to three more weeks to heal completely.
"When the virus wakes up from its sleep, it causes extensive damage to nerve cells," says Dr. Michael Oxman, an infectious disease specialist at UC San Diego. It's this damage that is believed to be responsible for the pain. Although the discomfort usually resolves by the time the rash has healed, it sometimes continues for months or even years, a condition called post-herpetic neuralgia.
Other potentially serious complications can occur as well. Reactivation of the virus in nerves near the eye can result in blindness; reactivation in facial nerves can lead to paralysis of the facial muscles. In rare instances, the virus can spread beyond the nerves, causing life-threatening infections of the spinal cord and brain.
Although no one can predict when the virus will reactivate or who will get shingles, the disease occurs more frequently -- and is more severe -- in older people. In fact, people older than 50 account for more than two-thirds of all cases of shingles.
Experts believe that the virus becomes active later in life because the body's natural defenses against it diminish over time.
