The varicella-zoster virus is the viral agent that causes chickenpox and shingles, according to the University of Maryland Medical Center. Chickenpox is a contagious childhood disease that only rarely causes severe problems, but afterwards, the varicella-zoster virus can lay dormant in the nerves and later reemerge as shingles.
The varicella-zoster virus is a type of herpes virus and is spread through contact with the rash or airborne droplets of the virus that result from sneezing, coughing and breathing, explains the University of Maryland Medical Center. A person is contagious from two days before the chickenpox rash appears until all the blisters have crusted over.
After the varicella-zoster virus results in chickenpox, the virus stays in the body, living in a dormant state in the nerve cells along the spine. When the immune system weakens, often from age, the virus can reawaken, causing the painful rash known as shingles. Approximately 30 percent of people who have had chickenpox develop shingles, and it is most common in individuals over the age of 60 with weaker immune systems, according to the University of Maryland Medical Center.
Certain preventive measures lower the risk of chickenpox and shingles. The chickenpox vaccine, known as Varivax, is often given at an early age to children, and the shingles vaccine, known as Zostavax, reduces the risk and severity of shingles, notes the University of Maryland Medical Center.