Having a close relative who has had a bout with shingles puts people at a heightened risk of suffering a similar outbreak, a new study finds.

A herpes virus called varicella zoster causes shingles and chickenpox. Since nearly everyone in the United States over age 25 has been exposed to the chickenpox virus, much of the population is at risk for shingles, which strikes in middle age and beyond. After causing a chickenpox infection, the virus lies dormant in nerves for decades. The virus can resurface as the nasty skin rash, blisters, itching and pain that mark a case of shingles. Some symptoms can last for weeks or months.

But only about one in five people exposed to chickenpox ultimately get shingles, says Stephen Tyring, a virologist and dermatologist at the University of Texas Health Science Center in Houston. Scientists suspect the immune system somehow keeps the virus bottled up in nerves better in some people than in others. People with compromised immune systems face a greater-than-average risk of shingles.

To test for a familial link, Tyring and his colleagues identified 504 people who had shingles and matched them with 523 volunteers who hadn’t. Everyone was over age 25; most fell between 46 and 75 years of age. The groups were matched overall for age, gender and race.

When the researchers compared family histories between the groups, they found that roughly 39 percent of the shingles patients had a close relative who also had had the disease. Only 11 percent of the controls did, they report in the May Archives of Dermatology. The researchers defined a close relative as a parent, child, sibling, uncle, aunt or first cousin.

A vaccine for chickenpox introduced in the United States in 1996 will probably knock down the risk of shingles for future generations, says Tyring. Meanwhile, a vaccine against shingles became available in 2006.

“Those with family members who have had shingles should consider being the first in line to be vaccinated,” he says. Insurance coverage for the shingles vaccine typically starts at age 60, but studies are under way to see whether this should be expanded to include 50-somethings, Tyring says.

Many scientists suspect that good immune system surveillance keeps the virus under wraps and locked indefinitely in nerve tissue in most people. In 2002, Finnish researchers reported evidence suggesting that having a specific variant form of a gene that encodes an immune protein called interleukin-10 might contribute to a person’s susceptibility to shingles. Interkeukin-10 inhibits inflammation in the body, but its role in shingles remains unclear.

The new study may spur more research aimed at sorting out this and other potential biomechanisms that could underlie susceptibility to shingles, Tyring says.

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