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Brain & Nervous System Health Center

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Viral Infections Linked to Dementia

Infection With Common Viruses May Increase Dementia Risk
WebMD Health News

Aug. 14, 2003 -- Certain viral infections may increase the likelihood of mental decline and dementia, especially among older adults with heart disease.

A new study shows that elderly people with evidence of infection with three common viruses -- viruses that cause cold sores, genital herpes, and a mono-like illness -- were more than twice as likely to suffer from dementia.

Researchers say the study adds new evidence to the theory that inflammation, which is part of the body's natural response to infection, plays an important role in the development of several health problems, such as heart disease, stroke, and dementia.

Viruses May Trigger Dementia

"Inflammation has been implicated in dementia, and viral infections could be a triggering factor," says researcher Timo E. Strandberg, MD, PhD, of the University of Helsinki in Finland, in a news release. "Our findings should be tested in other studies, but if these viruses are involved, there are existing therapies such as vaccination and antiviral drugs that could be used to prevent or treat dementia."

In the study, which appears in Stroke: Journal of the American Heart Association, researchers tested 383 elderly men and women with heart disease for the antibodies that are produced in response to infection with three common viruses: herpes simplex 1 (HSV1), herpes simplex type 2 (HSV2) and cytomegalovirus (CMV), and followed them for 12 months.

HSV1 causes cold sores, and HSV2 causes genital herpes. CMV is a virus that infects between 50% to 85% of American adults by age 40, but it causes few symptoms and no long-term health problems in most people.

The mental function of the participants was also assessed at the beginning and end of the study.

After testing for the viruses multiple times, researchers found that up to 60% of the participants tested positive for one or more or the viruses. And the more viral exposure, the higher the risk of dementia.

Those who had evidence of infection with all three viruses were 2.5 times more likely to have mental impairment than those with antibodies for less than three of the viruses.

Dementia was found in about 5% of people who were infected with one or none of the viruses, but those numbers grew dramatically with additional infections. Sixteen percent of those infected with two viruses had dementia and 27% of those exposed to all three had dementia.

The researchers also looked at whether infection with two common bacteria was related to dementia risk but found no association between bacterial infections and mental decline.

Because all of the participants also had heart disease, researchers say further studies should examine whether similar results are found in otherwise healthy individuals.

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