What is the Varicella-Zoster Virus?
You may not have heard of the Varicella-Zoster virus (VZV), but I bet you've heard of chickenpox. You've probably had them. Varicella-Zoster is actually the virus that causes chicken pox. Interestingly, it can also cause another malady you may have heard of: shingles.
The Varicella-Zoster virus is one of eight human herpes viruses. Other viruses in this family that you may recognize are Herpes Simplex Virus 1 (causes cold-sores) and Herpes Simplex Virus 2 (causes genital herpes). Although VZV is part of the herpes virus family, it does not cause genital herpes or cold-sores. It belongs to this family simply because it is similar in shape and size and reproduces in a similar fashion to other herpes viruses.
When you first become infected with VZV, the virus can cause a variety of symptoms including nausea, fever, headache, and the classic pox, or rash. The chicken pox rash is composed of hundreds of small, fluid-filled and reddened blisters which can itch horribly. These blisters often appear first on the face or trunk and then spread to other parts of the body through the bloodstream or by itching.
Catching the Virus
At this stage the virus is extremely contagious, capable of being spread by the tiny droplets made airborne by coughing and sneezing, or even by touching fluid in pox blisters. Infection usually occurs during childhood and only once. Varicella-Zoster viruses mutate very slowly (unlike influenza viruses) and therefore can rarely infect the same person twice.
However the VZV is sneakier than most viruses and can evade the immune system by hiding out in nerve cells of the dorsal root ganglia. Dorsal root ganglia are bundles of nerves which transmit sensory information from the skin to the brain. The nervous system is one of the few places the immune system doesn't patrol, allowing those microorganisms which can invade it to hide out indefinitely. This absence of activity is called latency.
Shingles (Herpes Zoster)
Anyone who has had chicken pox can also develop shingles. Shingles is the condition which results when the latent VZV is reactivated. The reason for such reactivation is unclear, but appears to be related to immune function. As the immune system is weakened by medications, immunodeficient diseases, stress or aging, we become more susceptible not only to infection but also re-infection.
When the virus becomes active again it travels along sensory nerves, causing sensory loss, pain, and other neurological symptoms. If the virus particles happen to invade the surrounding skin a localized rash of red blisters results. Shingles rashes usually appear along the trunk, coinciding with the location of dorsal root ganglia.
Because shingles is the result of a reactivated VZV it cannot be spread as shingles to another person. However when shingles is in the blisters phase, someone who has never had chicken pox (and therefore never encountered VZV) can catch the virus and develop chicken pox. Shingles is not contagious through coughing, sneezing, or casual contact, though. For further information on the Varicella-Zoster Virus, such as methods of treatment, read some of our other articles.