Why People with Shingles Feel Pain

In most cases, chickenpox is a benign childhood infection with symptoms that disappear within 10 days. However, the Varicella zoster virus (VZV) that causes it remains dormant in the patient forever. In some cases, the virus can be reactivated years later, causing a different disease known as herpes zoster, or shingles.

One of the first and most unpleasant symptoms of shingles is neuralgia, or constant intense pain affecting mainly the nerves of the chest and neck, the trigeminal nerve in the face, and the lower back. The pain may be accompanied by paresthesia, a feeling of pins and needles, tingling, prickling, itching, numbness, burning and/or cold). A painful blistering skin rash often develops.

Researchers affiliated with the University of São Paulo (USP) have published a study in The Journal of Neuroscience describing how the immune mechanisms triggered by the reactivated virus change the way that sensory neurons work. The authors say that their discoveries lay a foundation for novel treatments not only to combat acute pain but also to prevent it from becoming chronic, a condition known as post-herpetic neuralgia.

"Treatment for herpetic neuralgia is currently based on anti-inflammatory corticosteroids, which eliminate the symptoms but can impair control of the infection because they're immunosuppressants. Some of our findings suggest that therapies capable of blocking the action of an inflammatory mediator called tumor necrosis factor (TNF) that could act more selectively and so might be more efficacious," said Thiago Cunha, a professor at USP's Ribeirão Preto Medical School (FMRP) and co-author of the article.

Almost all adult humans carry VZV, he added. VZV usually lies dormant in the ganglia, clusters of sensory neurons that project to different parts of the body. An unexplained decrease in immunity leads to VZV reactivation in some people, causing inflammation of the ganglia. Shingles usually affects people over 60.

"Until the virus is transported along the nerves and skin lesions appear, which typically takes five to 10 days, the only symptom of shingles is neuralgia. This makes diagnosis difficult," Cunha said.

One of the contributions of this research is the validation of an animal model for studying the molecular mechanisms involved in herpetic neuralgia. Because VZV does not infect mice, the research group's experiments used herpes simplex virus type 1 (HSV-1), a related microorganism that can cause oral and genital skin lesions in humans.

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