I've had requests to re-run my column on shingles. I think the increased interest has been brought on by the television ads for the vaccine to help prevent shingles, which are quite accurate and compelling. I've had quite a few patients who have recently been suffering from this malady, two quite severely.

Shingles is caused by the Varicella-zoster virus (VZV). The virus is also known as chickenpox virus, varicella virus, and zoster virus. It is a member of the herpes virus family, of which eight strains are known to infect humans.

The biology of herpes viruses is very interesting. They infect humans through the skin and mucus membranes that line body openings. The initial or "primary" infection results shortly after exposure to the virus. This usually causes itching and redness of the skin followed by development of small fluid-filled blisters or "vesicles." Some readers may have seen chicken pox, though it is becoming a very rare disease since the advent of childhood vaccination to prevent the disease.

Interestingly, herpes viruses are never completely cleared from the body. Once the initial infection has subsided, the viruses travel to parts of the nervous system called ganglia that reside deep in the body. The viruses are quite happy playing Rip Van Winkle until they are awakened from slumber at some point in the future.

The appearance of the shingles rash can be explained by knowing a bit about the anatomy of the nervous system. The peripheral nervous system is made up of sensory and motor nerves that originate from the spinal cord that resides inside the spinal canal, formed from the vertebral bones. The sensory nerves are responsible for feeling (touch, pain, etc.) and leave the spinal cord at specific levels and branch out into segments of the skin called dermatomes (see diagram). These dermatomes stop at the midline of the body (i.e. there are right and left dermatomes at each level of the spinal cord).

Shingles is a condition where VZV is reactivated and begins to reproduce, causing a recurrent outbreak. As the viruses begin to multiply, they move from the ganglia near the spinal cord along the nerve fibers of one or more (usually adjacent) dermatomes to the surface of the skin.

When this reactivation occurs, the person usually feels some itching, burning or tingling along the involved dermatome(s). This is typically followed a day or two later by the formation of blistering skin and pain. The pain may precede the rash by a few days, sometimes fooling the patient and the doctor into thinking it's something else. It's important to note that Shingles almost always presents in a single dermatome on one side of the body and it is exceedingly rare for it to cross the center of the body (there is no truth to the adage that a person with shingles will die if the rash crosses the center of the body).

The varicella virus can also affect the nerves that supply sensation to the eye, a condition called herpes zoster ophthalmicus. These infections can be quite severe and can lead to a scarred cornea that may require corneal transplantation. People with shingles on the tips of their noses often have involvement of the cornea as well.

Shingles may last a week or two, sometimes longer. Unfortunately, about 15 percent of people, primarily the elderly, develop severe pain that persists after the rash is gone. This condition is called post-herpetic neuralgia (PHN). It can be extremely devastating and may require potent medication to keep it under control.

About a third of adults who have had a primary varicella infection will develop shingles. The main reason for developing a reactivation is reduced or waning immunity. Ninety five percent of adults in the U.S. have antibodies to VZV. This is either through natural immunity from having chicken pox as a child or from vaccine-associated immunity from receiving varicella vaccine.

As people age, their immune systems become weaker and they are less likely to be able to keep VZV in the resting stage. Other conditions such as infections or malignancies can also trigger an outbreak of shingles. However, most cases of shingles are not the result of severe underlying problems.

It is important to see a physician as soon as you suspect you may have shingles. There are anti-viral medications available that slow the spread of VZV and can also greatly reduce the risk of developing PHN. To be most effective, however, these medications should be started within 72 hours of the start of symptoms.

Since post-herpetic neuralgia can be so devastating, it is important for people over 60 years of age to be vaccinated against VZV with the vaccine Zostavax®. It is available in some doctor's offices or can be administered at most pharmacies. The vaccine costs close to $300, but most people who have had shingles would be very quick to say that it would be money well spent.

Dr. John Roberts is a local physician. His column appears weekly in the Times, and he has a daily health tip on the front page. Dr. Roberts is one of the owners of Sagamore News Media, parent company of The Times.