Shingles is childhood chickenpox waking up decades later along a single nerve
The virus behind chickenpox never fully leaves. It hides in nerve clusters beside the spine or at the base of the skull, sometimes for decades, then can travel back down one nerve to the skin. That is why the shingles rash forms a stripe on one side of the body and stops at the midline.
Shingles, also called herpes zoster, is caused by varicella zoster virus, a double-stranded DNA virus whose full genome was sequenced in 1986. It belongs to the same alpha herpesvirus subfamily as herpes simplex but is a different virus. After a first infection, usually in childhood, the immune system clears it from most of the body, yet it lingers in sensory ganglia. Researchers still do not know exactly what flips it back to activity. Infected cells keep making some viral proteins, so it has not even been proven that the virus is truly dormant rather than smouldering at a low level.
Tingling or pain often comes two to four days before any rash, alongside fever, headache and tiredness, which makes early diagnosis tricky. The rash then follows the strip of skin served by one nerve, a dermatome, most often on the torso. Blisters crust within seven to ten days, and the fluid can pass the virus to someone never exposed, who would develop chickenpox rather than shingles. When the ophthalmic branch of the trigeminal nerve is involved, in roughly 10 to 25 percent of cases, the eye can be affected. Around 2 percent of the general population, and 15 to 30 percent of people with weakened immunity, develop a widespread form.
It is common. About a third of people get shingles at some point, and around half of those who reach 85 will have at least one episode, though fewer than 5 percent have more than one. Age, weakened immunity and catching chickenpox before 18 months old raise the risk. Deaths are extremely rare, at 0.28 to 0.69 per million. Some people are left with lasting nerve pain, postherpetic neuralgia, for months or years.
Vaccines lower the risk by 50 to 90 percent depending on the type. Antivirals such as aciclovir can shorten an episode if started within 72 hours of the rash appearing, though evidence shows no significant effect on later nerve pain. A study using England's September 2013 age-based vaccine rollout as a natural experiment found fewer hospital shingles diagnoses among those eligible but no detectable change in dementia diagnoses.
Source: Shingles
