I've had a number of requests to re-run my column on shingles. I think the television ads for the vaccine to help prevent shingles, which are quite accurate and compelling, have spurred the increased interest. I've had quite a few patients who have been suffering recently from this malady, one 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. 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 just taking a nap until they are reactivated 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 nerves that originate from the spinal cord inside the bony spinal canal. These nerves are responsible for sensation (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).

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

When this reactivation infection occurs, the person usually feels some itching, burning or tingling along the course of the involved dermatome(s). This is typically followed a day or two later by the formation of blistering skin and pain. 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.

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 clouded cornea that may require corneal transplantation. People with shingles on the tips of their noses often have involvement of the cornea.

Shingles may last a week or two, or even 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 can require potent medication to keep it under control.

About a third of adults who have had varicella infection will develop shingles. The primary reason for developing reactivation infection 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 greatly reduce the risk of developing PHN. To be effective, however, these medications must be started within 72 hours of the start of symptoms.

Since post-herpetic neuralgia can be so devastating, it is important for people over 50 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 some pharmacies. The vaccine costs $160 - $200, but most people who have had shingles would be very quick to state that it would be money well spent.