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Shingles and Chickenpox (Varicella-Zoster Virus)
WHAT ARE SHINGLES AND CHICKENPOX (VARICELLA-ZOSTER VIRUS)?
Varicella-Zoster Virus
Shingles and chickenpox were once considered separate disorders. It is now known 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 (Chicken Pox). When patients with chickenpox cough or sneeze, they expel tiny droplets that carry the
virus, which in this early form is referred to as varicella virus. If a person who has never had chickenpox or
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.
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Herpes Zoster (Shingles).
The 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 has properties that allow it
to 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, however, can also spread to the spinal cord
and into the bloodstream.
It is not clear why the virus reactivates in some people and not in others. In many cases, the immune system has
become impaired or suppressed from certain conditions such as AIDS or other immunodeficient diseases or from
certain cancers or drugs that suppress the immune system. Aging itself may increase the risk for shingles.
Other Herpes Viruses
The varicella-zoster virus belongs to a group of herpes viruses that includes seven human viruses (it also includes
animal viruses as well). Herpes viruses are similar in shape and size and reproduce within the structure of a cell. The particular cell depends upon the specific virus. The human herpes viruses are:
* Herpes Simplex virus (the most common).
* Varicella-zoster virus (VZV).
* Cytomegalovirus (CMV).
* Epstein-Barre virus (causes mononucleosis).
* Human herpesvirus type 6 (causes roseola).
* Human herpesvirus type 7 (HHV-7).
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 for a lifetime.