Shingles are more than just painful. A new study suggests that they may increase the risk of stroke.

Shingles is caused by reactivation of the chickenpox virus, also called varicella zoster virus, which lays dormant in nerve fibers. When it's reactivated, often by trauma or stress, the virus can produce very painful skin blisters.

It's estimated that roughly one out of five people will at some point in their lives suffer an attack of shingles.

Dr. Herng-Ching Lin, from Taipei Medical University, Taiwan and associates found that a bout of shingles raises the risk of stroke over the subsequent year by roughly 30 percent.

Varicella zoster virus is the only human virus known to replicate in arteries in the brain, they note in a report published Thursday in the journal Stroke. The virus is thought to spread along the nerve fibers to the blood vessels where it induces harmful inflammatory and blood-clotting effects.

Lin's team studied 7,760 individuals treated for shingles between 1997 and 2001 and 23,280 randomly selected "control" subjects.

Within a year after their first office visit for shingles, 133 study subjects (1.71 percent) had a first-ever stroke, compared with 306 control subjects (1.31 percent).

After accounting for factors that might influence the results, the researchers found that the risk of stroke was 31 percent higher in people who suffered a bout of shingles.

For patients with shingles involving the eyes, the risk of stroke was more than four times higher.

Lin and colleagues call for further studies to explore the underlying mechanisms for the association between shingles and stroke and possible intervention strategies.s