Re: Exactly how does the chicken pox virus damage nerves & tissues?

Dear April,

There are three possible explanations for the damage to your cornea from shingles (also known as Zoster). The virus that causes chicken pox and shingles is called Varicella-Zoster (also known as Human Herpesvirus 3). After we are infected with this virus we get the classical symptoms of chicken pox with the itchy rashes etc and then the virus becomes latent in our nerve cells. That means that the virus is still present in our bodies even though we have 'recovered' from chicken pox. The virus is able to remain hidden in our nerve cells essentially forever and is not actively growing, the virus is actually trying to not replicate, that is what 'latent' means in this case. Sometimes (perhaps when we are stressed, the reason isn't really known) the virus is reactivated and starts to grow again. For a virus, growth means to replicate itself within the cells of its host (you and me!). As viruses replicate, they spread from cell to cell in order to replicate themselves even more, while, at the same time, our immune system tries to stop this spread.

Varicella-Zoster causes shingles when the viruses in the nerve cells begin to replicate, exit the nerve cell, and infect the cells immediately around the nerve. These cells include skin cells. Varicella-Zoster can cause damage by actually killing cells (the blisters that occur are a symptom of that) and in an indirect way by activating our immune systems which leads to inflammation that can damage to infected tissues.

That said, it is more likely that the damage to your cornea was caused by a third mechanism. One of the symptoms of shingles is neuralgia, which means that the nerve from which the virus is emerging is not working properly. When the nerve that detects sensations in the eye is not working properly we do not blink often enough and the eye dries out. When the eye dries out, cells in the cornea begin to die and this seems the most likely cause of the scarring in your cornea. If the eye can be kept moist by having a small humidified chamber placed over it the cornea should escape damage. Although it is possible that the virus spread from the nerve to the cells of the cornea and then killed them, I think it is less likely since blindness due to Zoster is extremely rare.

Here are is a picture of the villain: http://www.ncbi.nlm.nih.gov/ICTVdb/Images/ Fenner/herpes2.htm

and this is a link to the Big Picture Book of Viruses where you can find additional information: http://www.tulane.edu/~dmsander/Big_Virology/ BVHomePage.html