Shingles
Shingles is a blistering rash caused by the virus herpes zoster, which also causes chickenpox. After an attack of chickenpox the virus lies dormant in one of the sensory roots - called the dorsal root ganglion - in the spinal cord. Many years later, under the influence of conditions which cause the immunity to the virus to drop, it re-emerges, crawling down the nerve to affect the overlying skin, the dermatome, served by the nerve. While any nerve can be affected it more commonly affects the divisions of the trigeminal nerve that provides sensation to the face (and may therefore involve the eye and threaten sight by causing corneal ulceration) or those of the chest. The appearance of the rash is heralded by tingling or burning pain in the distribution of the nerve, and prompt treatment with specific anti-viral agents may abort, or reduce the severity of the attack. Adequate pain relief is necessary; the development of persistent pain after the attack, called post herpetic neuralgia or zoster associated pain, may require treatment with anti epilepsy agents. Once the attack is over immunity is restored and second attacks are much less common. People with shingles are infectious towards those who have not suffered chickenpox until all the blisters have crusted over. It is thought that they are not infectious to people who have had chickenpox - you can't catch shingles from someone with shingles, but there have been reports of clusters of cases.
Shingles may affect more than one nerve root at a time, but it only affects both sides of the body in people who are immunocompromised, which means their immune system is suppressed, usually by treatment to stop, for example, rejection of a transplanted organ.
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