Some Viruses Linked to Age-Related Dementia

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FRIDAY, Aug. 15, 2003 (HealthDayNews) -- Three widespread viruses appear to increase the risk that elderly people will suffer dementia, a new study contends.

People with a history of infection with at least two of the viruses -- two strains of herpes and a microbe called cytomegalovirus -- were about twice as likely to show significant mental decline during the one-year study as those infected with one or none of the pathogens.

Both herpes and cytomegalovirus are known to damage brain cells, so infection with either or both could lead to loss of neurons, and eventually dementia, the researchers say. In theory, drugs to treat existing infections or vaccines to prevent infections could prevent dementia, they add.

A report on the findings appears in the September issue of Stroke.

Scientists are increasingly coming to recognize that brain diseases, from Alzheimer's to Parkinson's, have at least some connection to inflammation.

"This is a very hot topic right now," says Dr. Howard Gendelman, director of the Center for Neurovirology and Neurodegenerative Disorders at the University of Nebraska Medical Center in Omaha.

The National Institutes of Health is sponsoring a symposium on research in this area later this year.

"In elderly patients, the local infection can penetrate the blood-brain barrier" -- a physical wall protecting the brain that becomes more porous with age, Gendelman says. "Inflammation can then seep into the brain and cause a secondary inflammatory response in the brain's immune cells."

This reaction can harm neurons and lead to dementia. It often does so in HIV patients, for example, he says.

Yet not all dementia results from infection, and not all infections lead to dementia. Genetics, nutrition and a host of other factors likely affect a person's susceptibility to brain inflammation, Gendelman says.

In the new work, Dr. Timo Strandberg, of the University of Helsinki, and his colleagues followed 383 elderly men and women with varying stages of blood vessel disease. More than 80 percent had a history of heart disease and 37 percent had had at least one stroke.

The researchers looked for signs of infection with three common viruses: herpes simplex 1, which causes cold sores; its sexually transmitted sibling herpes simplex 2; and cytomegalovirus, which can be harmful to babies in the womb but typically causes no problems for healthy adults.

Blood tests revealed that 48 people had evidence, in the form of proteins called antibodies, to one or none of the viruses; 229 had antibodies to two of the microbes; and 106 had signs of infection with all three viruses.

At the start of the study 58 people, or 15 percent, had cognitive trouble on a standard psychological exam. Those with antibodies to three viruses were 2.5 times more likely to fall into this group compared to people with fewer or no infections. The greater the level of antibodies, the more severe the dementia.

During the following 12 months, 150 people lost ground on the cognitive test. Again, history of infection was strongly linked to the likelihood of mental decline.

"Our results support earlier hypotheses that certain infections are associated with cognitive impairment and consequent dementia in old age," the researchers write. "In our elderly cohort, these viruses were probably contracted in childhood or young adulthood, but in modern society these are increasingly contracted later in life," they add. If the results are verified by future studies, "they may open new avenues to prevent dementia with antiviral drugs or possibly vaccinations."

Dr. Larry Goldstein, director of Duke University Stroke Center and a spokesman for the American Stroke Association, cautions the Finnish findings may not translate well to other groups of people. Not only did all the subjects have some form of vessel disease, but Finland is far more ethnically homogenous than, say, the United States. The study "is not applicable to the general population. It's limited to that narrow group of folks," he says.

Still, he adds, the Finnish researchers seem to show that the effects of infection on dementia are independent from other factors that influence mental ability and even other sources of inflammation.

More information

For more on dementia, try the National Library of Medicine or the Alzheimer's Association.