Finnish researchers tested 383 cardiovascular disease patients for antibodies to the viruses herpes simplex type 1 (HSV1), herpes simplex type 2 (HSV2), and cytomegalovirus (CMV). Antibodies in the blood indicate a current or previous infection by the viruses.
People with antibodies to two of the viruses had a 1.8 times greater risk of dementia than those infected by none or one of the viruses. Those infected by all three viruses had a 2.3 times higher risk. The researchers selected the three viruses because several studies have suggested a link between each of them and dementia.
"Inflammation has been implicated in dementia, and viral infections could be a triggering factor," says lead author Timo E. Strandberg, M.D., Ph.D. "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."
HSV1 causes cold sores and HSV2 is a sexually transmitted disease. CMV infects between 50 percent and 85 percent of U.S. adults by age 40, but it causes few symptoms and no long term health consequences in most healthy persons if they acquire it after birth.
The study involved participants in Finland's Drugs and Evidence-Based Medicine in the Elderly (DEBATE) study, an effort to seek out prevention strategies for several diseases.
All participants had atherosclerosis and lived at home when they began the study. Their average age was 80; 65 percent were female; 82 percent had coronary artery disease, and 37 percent had suffered at least one stroke.
As part of the DEBATE study, researchers assessed patients' cognitive abilities each year using two well established tests, the Mini-Mental State Examination (MMSE) and the Clinical Dementia Rating (CDR). Cognitive impairment is associated with dementia in old age.
Scientists compared the MMSE and CDR scores of patients when they entered the DEBATE study with the scores of 348 patients who were alive and retested one year later.
The maximum score on the MMSE is 30, and a score below 24 points usually indicates clinically significant cognitive impairment, says Strandberg, a senior lecturer at the University of Helsinki and a senior researcher at the Academy of Finland.
"We found a significant association between cognitive status and the viral burden at baseline," Strandberg says. At baseline, participants with exposure to all three viruses were 2.5 times more likely to have cognitive impairment than those with antibodies to fewer than three. MMSE scores declined as viral burden increased: average MMSE was 26.9 for those showing infection by zero or one virus; 26.5 for those with antibodies to two viruses, and 25.8 for participants with antibodies to all three of the viruses. The median MMSE score for those entering the DEBATE study was 27 with 58 participants scoring below 24. Forty-eight individuals had antibodies to none or one of the viruses; 229 showed previous infection by two viruses; and 106 had antibodies to all three.
In addition, abnormal clinical dementia rating scores were found in 4.9 percent of participants with exposure to zero or one virus, in 16.2 percent of those exposed to two viruses, and in 26.9 percent of participants exposed to all three.
At one year, the risk for cognitive impairment was 2.3 times higher for people with antibodies to all three viruses and 1.8 times higher for those with antibodies to two compared to those with one or no antibodies.
Researchers also tested patients for infection by the two bacteria: Chlamydia pneumoniae, which causes respiratory diseases, and Mycoplasma pneumoniae, which causes "walking pneumonia." The microorganisms have been associated with atherosclerosis and late onset dementia, including Alzheimer's, which is increasingly considered a vascular disease, Strandberg says.
They found that 79 patients (20.6 percent) had no antibodies to either; 182 (47.5 percent) had antibodies to one of the bacterium; and 122 (31.9 percent) had been infected by both. However, the researchers found no association between bacterial infection and a patient's decline in cognitive powers.
"Either bacteria are not involved, or we could not discern their effects," he says. Because all of the participants suffered from cardiovascular disease, the researchers could not determine whether the ailment played a role independent of the viruses in lowering the cognitive scores of participants.
Co-authors are Kaisu H. Pitkala, M.D., Ph.D.; Kimmo H. Linnavuori, M.D., Ph.D.; and Reijo S. Tilvis, M.D., Ph.D.
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Editor's note: For more information on stroke, visit the American Stroke Association Web site: http://www.