Shingles, also called herpes zoster, occurs when a previous infection with the herpes zoster virus (the previous infection being a case of chickenpox, caused by varicella-zoster or VZV) reactivates. The resulting infection causes a painful, localized rash, usually with blisters on top of reddish skin. Herpes zoster viruses are not the same viruses that cause genital herpes.
After an individual recovers from chickenpox, the virus remains dormant in the body, usually at the roots of nerves that control sensation. In about 20 percent of the previously infected population, the virus will reactivate, years or even decades after the childhood (or adult) chickenpox infection clears up. What causes this reactivation in some, but not others, remains unknown.
Once the reactivation occurs, the virus travels along the sensory nerves to the skin, causing the shingles disease and rash. The majority of people who develop shingles are older than 60 years of age, but it does occur in younger people and even in children.
What Are the Risk Factors?
Anyone who has had the chickenpox infection or who has received the chickenpox vaccine (with live, attenuated virus) may carry the herpes zoster virus that causes shingles.
People older than 50, those with cancer, HIV/AIDS or organ transplant patients are at higher risk for getting shingles, as are those who have a decreased ability to fight off infection because of chronic stress or immune deficiency. Chronic fatigue can play a role in the reactivation of the herpes zoster virus.