A person who carries certain antibodies of the herpes simplex virus may be at double the risk for Alzheimer’s disease, according to two new Swedish studies.
“The identification of a treatable cause [herpes simplex] of the most common dementia disorder is a breakthrough,” said lead researcher Dr. Hugo Lovheim, an associate professor in the department of community medicine and rehabilitation at Umea University in Sweden.
“Whether treatment of herpes infection with antiviral drugs may slow the Alzheimer’s progression is not known, but is certainly worth investigating in clinical studies,” he said.
Herpes simplex is the common infection that causes cold sores. The virus, which affects up to 90 percent of the population, is lifelong but not always active. According to the researchers, the herpes virus weakens the immune system, allowing the virus to spread to the brain, which may start the process toward dementia.
The first study involved nearly 3,500 people who were followed for an average of 11 years; the researchers found that those who had certain antibodies to a herpes infection doubled their risk for developing Alzheimer’s disease.
In the second study, blood samples were taken from 360 Alzheimer’s patients an average of 9.6 years before being diagnosed with the disease.
When the researchers compared these with samples taken from people without Alzheimer’s, they found no association between Alzheimer’s and herpes infection. However, when they looked only at people who had their blood taken 6.6 years prior, they found a significant link between the herpes virus and the risk of developing Alzheimer’s disease.
“I think herpes virus causes a significant proportion of all cases of AD — about 40 to 50 percent — according to our data,” Lovheim said.
Lovheim said the findings show more than a chance association and may indicate a causal relationship.
“I think a causal relationship is likely, but like all epidemiological studies, there might always be confounders one has not thought about or not measured,” he said.
“In a few years we hope we will be able to start clinical studies to investigate whether antiviral drugs might slow the progression of Alzheimer’s disease,” he said.
However, Greg Cole, Ph.D., the associate director of the Geriatric Research and Clinical Center at the University of California, Los Angeles Alzheimer Disease Research Center in Los Angeles, isn’t convinced.
“More than 90 percent of the population has antibodies to herpes, and they are not all destined to develop Alzheimer’s disease,” he said.
However, an immune response or infection connection between herpes and Alzheimer’s disease is possible, Cole noted.
“Recent genetic studies have implicated variants of several genes controlling immunity with increased Alzheimer’s disease risk. These new results warrant a closer look in larger populations,” Cole said.
The studies were published in the journal Alzheimer’s & Dementia.