virus of the Herpes family .known as varicella-zoster virus (VZV).Other Herpes Viruses

Shingles and chickenpox were once considered separate disorders. Researchers now know that they are both caused by a single virus of the herpes family, known as varicella-zoster virus (VZV). The word herpes is derived from the Greek word "herpein," which means "to creep," a reference to a characteristic pattern of skin eruptions. VZV is still referred to by separate terms:

Varicella: The primary infection that causes chickenpox
Herpes zoster: The reactivation of the virus that causes shingles
Varicella (Chickenpox). When patients with chickenpox cough or sneeze, they expel tiny droplets that carry the virus. If a person who has never had chickenpox or never been vaccinated inhales these particles, the virus enters the lungs. From here it passes into the bloodstream. When it is carried to the skin it produces the typical rash of chickenpox.

Chickenpox is caused by the varicella-zoster virus, a member of the herpes virus family. The same virus also causes herpes zoster, or shingles, in adults. Chickenpox is extremely contagious, and can be spread by direct contact, droplet transmission, and airborne transmission. Symptoms range from fever, headache, stomach ache, or loss of appetite before breaking out in the classic pox rash. The rash can consist of several hundred small, itchy, fluid-filled blisters over red spots on the skin. The blisters often appear first on the face, trunk, or scalp and then spread to other parts of the body
Herpes Zoster (Shingles). The varicella virus also travels to nerve cells called dorsal root ganglia. These are bundles of nerves that transmit sensory information from the skin to the brain. Here, the virus can hide from the immune system for years, often for a lifetime. This inactivity is called latency.

If the virus becomes active after being latent, it causes the disorder known as shingles. The virus in this later form is referred to as herpes zoster. The virus spreads in the ganglion and to the nerves connecting to it. Nerves most often affected are those in the face or the trunk. The virus can also spread to the spinal cord and into the bloodstream.

It is not clear why the varicella virus reactivates in some people but not in others. In many cases, the immune system has become impaired or suppressed from certain conditions such as AIDS, other immunodeficient diseases, or certain cancers or drugs that suppress the immune system. Aging itself increases the risk for shingles.

Other Herpes Viruses
The varicella-zoster virus belongs to a group of herpes viruses that includes eight human viruses (it also includes animal viruses). Herpes viruses are similar in shape and size and reproduce within the structure of a cell. The particular cell depends upon the specific virus. Human herpes viruses include herpes simplex virus 1 (HSV-1), which causes cold sores, and herpes simplex virus 2 (HSV-2), which causes genital herpes. Cytomegalovirus (CMV), which causes mononucleosis and retinitis, and Epstein-Barre Virus (EBV), another cause of mononucleosis, are also human herpes viruses.

All herpes viruses share some common properties, including a pattern of active symptoms followed by latent inactive periods that can last for months, years, or even a lifetime.