What is Shingles?
Scientists call the virus that causes chickenpox/shingles varicella-zoster virus or VZV. The word "varicella" is derived from "variola," the Latin word for smallpox, another infectious disease that can resemble chickenpox. (Smallpox is a highly contagious and often fatal disease that has disfigured or killed millions of people, especially during the Middle Ages.) "Zoster" is the Greek word for girdle; shingles often produces a girdle or belt of blisters or lesions around one side of the waist. This striking pattern also underlies the condition's common name: shingles comes from "cingulum," the Latin word for belt or girdle.
VZV belongs to a group of viruses called herpesviruses. This group includes the herpes simplex virus that causes cold sores, fever blisters, mononucleosis, genital herpes (a sexually transmitted disease), and Epstein-Barr virus involved in infectious mononucleosis. Like VZV, other herpesviruses can hide in the nervous system after an initial infection and then travel down nerve cell fibers to cause a renewed infection. Repeated episodes of cold sores on the lips are the most common example.
As early as 1909, scientists suspected that the viruses causing chickenpox and shingles were one and the same. In the 1920s and 1930s, the case was strengthened by an experiment in which children were inoculated with fluid from shingles blisters. Within 2 weeks, about half of the children developed chickenpox. Finally, in 1958, detailed analyses of the viruses taken from patients with either chickenpox or shingles confirmed that the viruses were identical.
Virtually all adults in the United States have had chickenpox, even if it was so mild as to pass unnoticed, and thus may develop shingles later in life. In the original exposure to VZV (chickenpox), some of the virus particles leave the blood and settle into clusters of nerve cells (neurons ) called sensory ganglia, where they remain for many years in an inactive (latent) form. The sensory ganglia, which are adjacent to the spinal cord and brain, relay information to the brain about what the body is sensing - heat, cold, touch, pain.
When the VZV reactivates, it spreads down the long nerve fibers (axons) that extend from the sensory cell bodies to the skin. The viruses multiply, the telltale rash erupts, and the person now has herpes-zoster, or shingles. With shingles, the nervous system is more deeply involved than it was during the bout with chickenpox, and the symptoms are often more complex and severe.
