By Peggy O'Farrell
The Cincinnati Enquirer

David Letterman probably isn't laughing about another go-round with the virus that causes chickenpox: A nasty case of shingles has kept the late-night star off the air.

Shingles looks like chickenpox, but it hurts a lot more. The two diseases are caused by the same virus, which remains dormant in the nerve tissues. Herpes zoster (or varicella-zoster virus), like herpes simplex (the virus that causes cold sores), can be reactivated by stress or illness. The first time you get it, it's chickenpox. In its reincarnation, it's shingles.

Letterman is one of the million or so Americans afflicted by shingles every year. The infection can be intensely painful, but it's rarely life-threatening. Letterman's infection settled in his eye.

"Adults can have pain that lasts for months afterward, even after the blisters are gone," said Dr. Omer Berger of Cincinnati Children's Hospital Medical Center. "It's really very annoying. It's really not something you want to get."

Here are the facts on the nasty bug:

Question: What is shingles?

Answer: It's an infection caused by the herpes zoster virus, the same virus that causes chickenpox. Shingles occurs in people who have had chickenpox when the virus, which lies dormant in the body, is reactivated. Older people usually get shingles, but it can occur in younger people or people with weakened immune systems.

Q: What are the symptoms?

A: The first sign is usually a tingling feeling, itchiness or a stabbing pain on the skin. A few days later, a band or patch of raised dots appears on the side of the trunk or face. The rash usually follows nerve fibers and develops on one side of the body.

The rash develops into small, fluid-filled blisters that dry and crust over within several days. When the rash is at its worst, symptoms range from mild itching to extreme and intense pain.

Q: What's the prognosis?

A: Shingles usually isn't dangerous to healthy people, and there are rarely complications. The rash and pain usually go away within three to five weeks.

Sometimes, the infection can cause partial paralysis of the facial muscles, which is usually temporary. It also can damage the ear or cause encephalitis (inflammation of the brain). People with shingles on the upper half of the face should see a doctor, because the infection can sometimes damage the eyes.

Q: How can shingles affect the eye?

A: The virus might follow the nerve pathway connected to the eyes. The rash can spread from the forehead or cheek to the eyelids and may cause redness of the mucus membrane that covers the white of the eye. It also can scratch or scar the cornea, increasing the risk of bacterial infection. Shingles can cause inflammation inside the eye and can affect the optic nerve or retina.

Q: Is shingles contagious?

A: Someone who's never had chickenpox can develop chickenpox - but not shingles - after coming into contact with someone who has shingles.

Q: Is there any treatment?

A: Treatment includes antiviral drugs, steroids, antidepressants, anticonvulsants and topical agents.

Antiviral drugs, such as acyclovir, can significantly reduce the severity of an infection if they're used immediately. They may also prevent the painful aftereffects of shingles, known as postherpetic neuralgia.

Q: What is postherpetic neuralgia?

A: About 20 percent of people who get shingles continue to experience long-lasting pain (postherpetic neuralgia) months, or even years, after the infection clears up. The virus that causes shingles can damage the nerve fibers, resulting in mild to severe pain. For most people, the pain lessens over time, and there are many treatment options for pain relief, including antidepressants, opioids, anticonvulsants and a topical lidocaine patch.

The older a person is when he or she gets shingles, the more likely he or she is to develop postherpetic neuralgia. Three of four people over 70 develop postherpetic neuralgia after shingles, compared with one of four people ages 55 to 60.

Q: Can you get shingles more than once?

A: Most people who get shingles only have it once. But people with impaired immune systems because of AIDS, cancer, etc., may suffer repeated infections.

Sources: The National Institute of Neurological Disorders and Stroke, Aftershingles.com, and the Steen-Hall Eye Institute.