Shingles, the nerve rash in adulthood caused by reactivation of the chickenpox virus, is an independent risk factor for stroke and other blood clot events, the largest study to confirm the association has found.

Publishing their findings in Neurology, the journal of the American Academy of Neurology, the researchers found that shingles was a risk factor for stroke and transient ischemic attack (TIA, a mini-stroke).

The increased risk was independent of other factors known to raise the chances of vascular events, including obesity, smoking and high cholesterol.

The size of the increase in risk was by three-quarters for some, the researchers say.

People under 40 years of age who had had shingles were 74% more likely to have a stroke than those who had not suffered the rash.

Shingles, also called herpes zoster, is caused by the same varicella-zoster virus that leads to chickenpox. The infection lies dormant in nerve roots, but in cases of shingles, which occurs in adulthood, it is reactivated in the skin, causing a rash and the neuropathy pain known as postherpetic neuralgia.

People younger than 40 years "were significantly less likely to be asked about vascular risk factors than were older patients" in the study, which also looked at heart attack risk.

Study author Dr. Judith Breuer, from University College London in the UK, calls for stroke monitoring in people who get the shingles rash, particularly if at a younger age. She says:

"Anyone with shingles, and especially younger people, should be screened for stroke risk factors.

The shingles vaccine has been shown to reduce the number of cases of shingles by about 50%. Studies are needed to determine whether vaccination can also reduce the incidence of stroke and heart attack."

The study authors say that the association between shingles and stroke may persist in people over 40, too - it is just that such an effect could be hidden by the greater interventions in general that prevent stroke in older groups.

Questions over wider immunization against shingles

Current recommendations from the US Centers for Disease Control and Prevention (CDC) are that anyone aged 60 years and older receives the herpes zoster vaccine.

"The role for vaccination in younger individuals with vascular risk factors needs to be determined," Dr. Breuer says, while recognizing that multiple variables affect the chances of vascular events, such as stroke, TIA and heart attack:

"What is also clear is that factors that increase the risk of stroke also increase the risk of shingles, so we do not know if vaccinating people can reduce the risk of stroke per se."

Why is shingles virus associated with stroke?

As background to the study, the authors describe previous research showing that the varicella-zoster virus affecting the visual branch of the facial nerve (or ophthalmic branch of the trigeminal nerve) had spread to cerebral arteries in shingles patients who went on to have a stroke.

Similar pathology findings relating to the shingles virus and artery damage revealed at autopsy have been found when the infection is wider than ophthalmic sites, and even in cases of no rash, the authors add.

The researchers established their study to confirm a link using data from large numbers of people.

Analysis of almost 320,000 patient records

The data in the study were extracted from patients who had routinely attended 464 general practices in the UK between 2002 and 2010.

Nearly 107,000 cases of shingles were found among 3.6 million active patients, and the data collected spanned 23.7 years, with the average span of 6.3 years.

These cases were matched with controls who did not have shingles - over 213,000 patients of the same mix of age, sex and GP practice.

Concluding the paper, the authors write:

"Overall, these data add to the growing body of evidence linking varicella-zoster virus, a ubiquitous pathogen that establishes persistent infection in more than 95% of individuals, to vascular disease."