Varicella zoster virus (VZV) is the virus that causes chicken pox, usually a relatively minor childhood illness.  Unlike other viruses that are cleared from our bodies after infection, VZV stays in our sensory nerve cells forever.  Over the subsequent decades our immunity to VZV wanes.  When our immunity falls too low, VZV can reactivate and cause shingles.  Shingles is a painful blistering rash along the distribution of one sensory nerve.  The rash resolves in a few weeks, but in some older pat...