Shingles (herpes zoster) causes an extremely painful red blistering rash along the path of a nerve, usually about the head, the neck or the trunk on one side of the body. Shingles results from the varicella-zoster virus, the same virus that causes chickenpox. Chickenpox, most common in childhood, causes a scattered itching blistering rash with lesions that crust over and heal in one to three weeks. Chickenpox does not recur, so infection confers immunity. However, the virus remains behind in latent (inactive) form in the nerve cells near the brain and spinal cord and can reactivate, usually after age 50 to cause shingles, a much more serious condition.
Normally, the immune system of the body prevents reactivation of the latent virus, but as people age, their immune systems can become less effective. Some immunosuppressive diseases (such as HIV/AIDS), some cancers (leukaemia, lymphoma, and Hodgkin's disease) and treatments (chemotherapy and steroids) can impair the immune system, resulting in reactivation of the dormant virus. For example, according to physicians Stephen J. McPhee and Maxine A Papadakis in "Current Medical Diagnosis and Treatment," people with HIV are 20 times more likely to develop shingles than the general public.
As the virus reactivates and travels along the nerve pathways to the skin, it causes severe pain, which is followed within about 48 hours by redness of the skin and a blistering rash. The clear fluid in the lesions changes to pus, and the lesions open, dry and form crusts, eventually healing over a period of about a month.
While antiviral drugs, such as acyclovir or valacyclovir, may shorten the duration of a shingles episode and reduce symptoms, the drugs do not kill the virus. As shingles clears, the virus retreats back to the nerve root and returns to the latent form. Most people have only one episode of shingles, but it can recur, especially with HIV/AIDS. Mayo Clinic states that some people develop postherpetic neuralgia, chronic severe debilitating pain along the pathway of the nerve, persisting for weeks, months or even years after the rash clears. This is not, however, a recurrence, but it rather results from damage to the nerve fibres during the initial shingles infection. The Centers for Disease Control and Prevention recommend Zostavax, the shingles vaccine, for adults over 60. The CDC reports that the vaccine reduces initial and recurrent shingles infections by 51 per cent and reduces incidents of postherpetic neuralgia by 67 per cent.