Cause for Herpes Zoster

Reinfection with the varicella-zoster virus -- the same virus that causes chickenpox -- is what causes herpes zoster. Risk factors for herpes zoster include having had chickenpox or the chickenpox vaccine, as well as having a weakened immune system due to HIV infection, chemotherapy or radiation treatment, transplant operations, or stress.

What Causes Herpes Zoster?

Herpes zoster (also known as shingles) has only one cause. The disease is caused by a reinfection with the varicella-zoster virus. This is the same virus that causes chickenpox. Infection with this virus tends to occur during different decades of a person's life.
 

Understanding the Varicella-Zoster Virus

Varicella-zoster is part of the herpesvirus family. This group of viruses includes the herpes simplex virus (HSV) that causes cold sores, fever, blisters, genital herpes (a sexually transmitted disease), and the Epstein-Barr virus involved in infectious mononucleosis.
 
As early as 1909, a German scientist suspected that the viruses causing chickenpox and herpes zoster were one and the same. In the 1920s and 1930s, the case was strengthened.
 
As part of an experiment, children were inoculated with fluid from the lesions of people with herpes zoster. Within two weeks, about half the children came down with chickenpox. Finally, in 1958, detailed analyses of the viruses taken from people with either chickenpox or herpes zoster confirmed that the viruses were identical.
 
So how is herpes zoster caused by the same virus that causes chickenpox? To understand this, it may be helpful to understand the "reactivation" of the varicella-zoster virus.
 

How Does Reactivation of the Varicella-Zoster Virus Lead to Herpes Zoster?

After an attack of chickenpox, the varicella-zoster virus moves up into the nerves, where it settles down in an inactive form (known as a latent form).
 
It "lies down" inside specific nerve cells (neurons) that relay information to the brain about what your body is sensing -- such as whether your skin feels hot or cold, whether you've been touched, or whether you're feeling pain. These nerve cells lie in clusters (ganglia) adjacent to the spinal cord and brain, and are one type of sensory neurons.
 
As we get older, it is possible for the varicella-zoster virus to "come alive." When this happens, the virus "reactivates" and then moves down the nerves to cause the symptoms of herpes zoster. Research scientists are still trying to understand why this happens and why it happens in some people and not in others.
 
Herpes zoster is most common in people over the age of 50. However, if you have had chickenpox or the chickenpox vaccine, you are at risk of developing herpes zoster. This disease is also more common in people with weakened immune systems from HIV infection, chemotherapy or radiation treatment, transplant operations, or stress.
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