Dementia association detected between herpes viruses and Alzheimer's

Researchers find a link between Alzheimer's and herpes viruses

More and more people are currently suffering from Alzheimer's. Researchers have now discovered that the presence of herpes viruses in the brain seems to be linked to the development of Alzheimer's.

The scientists of the Icahn School of Medicine at Mount Sinai in New York found in their current study that herpes viruses seem to favor the development of Alzheimer's disease. The physicians published the results of their study in the English-language journal "Neuron".

Herpes viruses are known to cause unpleasant cold sores. Experts have now found that herpes viruses may also be involved in the development of Alzheimer's. (Image: Cherries / fotolia.com)

Do viruses influence Alzheimer's disease??

Viruses have long been suspected of having an impact on the development of Alzheimer's. Physicians were now trying to analyze such a relationship more accurately. They found that in the early stages of Alzheimer's disease virus strains occur more frequently in the brains of those affected. However, it is still uncertain whether the virus is a trigger or a symptom of the disease, the experts explain.

HHV-6A and HHV-7 were more common in Alzheimer's brains

The researchers found that traces of the HHV-6A and HHV-7 variants, which are remotely associated with cold sores and genital herpes, are more common in the brains of patients with Alzheimer's disease. The presence of these viruses in the brain has been implicated in Alzheimer's disease, a finding that challenges conventional theories on the occurrence of dementia.

A new mechanism was found

Researchers identified a mechanism by which viruses could cause the typical damage to nerve cells in Alzheimer's disease. The results are based on tests of the brain tissue of a total of nearly 1,000 subjects. The two above-mentioned strains of herpesviruses were much more common in the brains of early-stage Alzheimer's disease compared to healthy controls, the authors of the study say. However, there is disagreement among experts as to whether the viruses are an active trigger of the disease or whether the brains of people already on their way to Alzheimer's are simply more susceptible to infection.

About one million people in Germany suffer from Alzheimer's disease

Alzheimer's represents the most common form of dementia worldwide. Of course, there are also many people with Alzheimer's in Germany. Experts believe that about one million people in this country suffer from the disease. The early diagnosis of Alzheimer's disease is often problematic, because the damage to the brain progresses very slowly for the time being. This causes the disease to go undetected for a long time.

In the brain, herpesviruses affect the activity of different genes?

The viral genomes were detectable in approximately 30 percent of the brains of Alzheimer's patients. In comparison, viruses were virtually undetectable in the brains of the healthy control group, study author Professor Sam Gandy of the Icahn School of Medicine at Mount Sinai, New York, explains. The study also suggested that the presence of herpesviruses in the brain could influence or control the activity of various genes associated with increased Alzheimer's risk.

The scientists did not really look for a link between viruses and dementia. Instead, they hoped to find genes that are unusually active in the brains of people with the earliest stage of Alzheimer's disease. But when they looked more closely at brain tissue and compared people with early-stage Alzheimer's and healthy controls, the most striking differences in gene activity were found not in human genes but in genes belonging to two herpes virus strains, HHV6A and HHV7.

Increased virus concentration in the brain could trigger an immune reaction

The experts originally looked for molecular abnormalities in the development of Alzheimer's disease. For this purpose, four human brain areas affected by the disease were examined in more detail. The physicians found that the genetic makeup of people with some form of dementia was more likely to have human herpesviruses (HHV) types 6a and 7. An analysis of further data sets could also establish such a connection. The experts actually did not look for viruses at the beginning of the study. But the virus jumped right into the eye, says study author Ben Readhead of the Mount Sinai School of Medicine in New York. Further investigation revealed that the viruses could affect brain metabolism. An increased virus concentration in the brain could trigger an immune response that promotes the onset or progression of Alzheimer's, adds the expert.

Results were confirmed several times

The authors explain that the team initially reacted with surprise and skepticism to the results. It was attempted to be conservative in interpreting the results and to reproduce the results in three different brain banks. The results could also be confirmed with the duplicate repetition of the examination. The physicians could at least recognize that the diseased brains carry these viral genomes.

Herpes genes enhance the activity of Alzheimer's genes

The scientists could not prove that viruses actively contribute to the onset of the disease, but they found a plausible mechanism for how this could happen. It has been found that some of the herpes genes enhance the activity of several known Alzheimer's genes. Previous studies have already suggested that viruses could be linked to Alzheimer's disease. But the current detailed analysis of human brain tissue continues this research, showing a relationship between the viruses and the activity of genes involved in Alzheimer's, as well as the brain changes, molecular signals, and symptoms associated with the disease, the experts explain.

Alzheimer's is not contagious

The detected viruses are not the same as those causing the known cold sores. They are among much more common forms of herpes that almost every person carries. These forms of herpes usually cause no problems, explain the doctors. The study also does not suggest that Alzheimer's disease is contagious or how a virus can be transmitted from human to human. In addition, there was no evidence that the risk of developing dementia was increased by the appearance of cold sores. (As)