Shingles and chickenpox 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 causes two different clinical illnesses:
- Varicella, or chickenpox, develops after an individual is exposed to VZV for the first time.
- Herpes zoster, or shingles, develops from reactivation of the virus later in life, usually many decades after chickenpox.
Most people get chickenpox from exposure to other people with chickenpox. It is most often spread through sneezing, coughing, and breathing. It is so contagious that few nonimmunized people escape this common disease when they are exposed to someone else with the disease.
When people with chickenpox cough or sneeze, they expel tiny droplets that carry the varicella 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.
People can also catch chickenpox from direct contact with a shingles rash if they have not been immunized by vaccination or by a previous bout of chickenpox. In such cases, transmission happens during the active phase when blisters have erupted but not formed dry crusts. A person with shingles cannot transmit the virus by breathing or coughing.
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-zoster 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.Click the icon to see an image of shingles.
If the virus becomes active after being latent, it causes the disorder known as shingles or 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.
Shingles itself can develop only from a reactivation of the varicella-zoster virus in a person who has previously had chickenpox. In other words, shingles itself is never transmitted from one person to another either in the air or through direct exposure to the blisters.
It is not clear why the varicella-zoster 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 immunodeficiency 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 usually causes cold sores, and herpes simplex virus 2 (HSV-2), which usually causes genital herpes. Cytomegalovirus (CMV), which causes mononucleosis-like illness and retinitis, and Epstein-Barre Virus (EBV), the cause of classic 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. [For more information, see In-Depth Report #52: Herpes simplex.]