Shingles Health Article

Causes and symptoms

Shingles is caused by the varicella-zoster virus (VZV), also known as HHV-3. VZV is genetically similar to the herpes simplex viruses, the type of viruses that causes cold sores and genital herpes. Herpes simplex virus also takes up permanent residence in sensory nerve ganglia, but not in the dorsal root ganglia of the spine, as does VZV. In chicken pox, the virus is inhaled and begins replicating in the upper respiratory tract before spreading to the liver and other body systems.

Following primary infection, VZV remains as a symptomless infection in the dorsal root ganglia of the spinal cord. It may or may not become active again, that is, begin reproducing, later in life. Reactivation occurs more often in older people, probably as a result of decreased immune response with age. Reactivation may be symptomless, but usually causes shingles. Repeat episodes of shingles are rare (occurring in less than 4% of patients) because the immune system's response to VZV is boosted by a first shingles episode.

Chills, fever, malaise, gastrointestinal problems, and pain in the affected skin areas may precede appearance of skin eruptions by several days. Viral particles travel away from the spinal cord along the sensory nerves toward the skin, causing inflammation of those nerves, which may be painful. On the fourth or fifth day, skin vesicles begin to appear. The affected area is usually hypersensitive, and disabling pain (described as sharp, stabbing, or burning) may occur in the affected area. About the fifth day after appearing, the vesicles begin to crust or scab and the disease resolves within the next two weeks. There may be no visible aftereffects, although slight scarring from the vesicles may occur.

Especially in elderly patients, pain may persist for months or years after shingles has otherwise resolved. This pain, postherpetic neuralgia, is caused by damage to the dorsal root ganglia that renders them either spontaneously active (perceived as chronic pain) or hypersensitive to slight stimuli such as light touch.

VZV can become active in the cranial nerves as well as in the spinal ganglia. Involvement of branches of the trigeminal nerve (fifth cranial nerve) is most common. When the ophthalmic branch of the trigeminal nerve is involved, this condition is called herpes zoster ophthalmicus. It can cause swelling of the eyelid, pain, and other complications involving the eye. Herpes zoster ophthalmicus can also lead to weakness or partial paralysis (hemiparesis) on the opposite side of the body from the nerve affected, possibly by inducing irritation of the blood vessels in the brain. Infection of cranial nerves by reactivated VZV can also affect the hearing. When this occurs, it is usually associated with facial palsy and is known as Ramsay-Hunt syndrome.

Large amounts of free virus (i.e., virus not held inside cells) is present in the fluid-filled vesicles or bumps that erupt on the skin during shingles. Thus, people who are not resistant to VZV are easily infected by contact with persons having an outbreak of shingles. A particular strain of VZV can remain latent for decades and then reappear as a new epidemic.