A study led by the Arizona State University and the Banner Alzheimer’s Institute has identified a surprising relationship between a chronic intestinal infection caused by cytomegalovirus and the development of Alzheimer’s disease in a specific group of people. This finding could open the door to antiviral treatments to combat this form of the disease.
Cytomegalovirus, a common virus that affects most humans at some point in their lives, can remain active in the intestine in some people. According to the study, published in the journal ‘Alzheimer’s & Dementia‘, the virus could travel to the brain through the vagus nerve, altering the immune system and contributing to changes associated with Alzheimer’s, such as amyloid plaques and tau tangles.
If the researchers’ hypotheses are confirmed, they will be able to evaluate whether existing antiviral drugs could treat or prevent this form of Alzheimer’s disease. They are currently developing a blood test to identify people who have an active cytomegalovirus infection and who could benefit from antiviral medication.
“We believe we have identified a unique biological subtype of Alzheimer’s that could affect between 25% and 45% of patients with this disease,” he explains. Ben Readheadco-author of the study.
The study also looked at the role of immune cells in the brain, called microglia. Although these cells initially protect the brain, their prolonged activation can cause chronic inflammation and neuronal damage, contributing to the progression of neurodegenerative diseases.
A recent study published earlier this year in ‘Nature Communications‘ revealed that the brains of Alzheimer’s patients have more CD83(+) microglia, immune cells related to infections. Researchers found that this condition is associated with intestinal antibodies directed against cytomegalovirus.
Blood test
Using human brain cell models, the researchers showed that cytomegalovirus increases the production of amyloid proteins and phosphorylated tau, characteristics of Alzheimer’s, and causes neuronal damage. The connection was confirmed in an independent group of patients, strengthening the hypothesis that cytomegalovirus contributes to the development of this disease.
Researchers are developing a blood test to identify people with chronic cytomegalovirus infections who could benefit from antiviral treatments. If the findings are confirmed, the use of existing antiviral medications could be evaluated to treat or prevent this subtype of Alzheimer’s.
Is cytomegalovirus to blame for Alzheimer’s disease in some people?
Cytomegalovirus can infect people of all ages. In most healthy people, the infection occurs without symptoms, but it can present as a mild flu-like illness. About 80% of people show evidence of antibodies by age 80. However, the researchers detected intestinal cytomegalovirus only in a subset of individuals, and this infection appears to be a relevant factor in the presence of the virus in the brain. For this reason, researchers point out that simply coming into contact with cytomegalovirus, which happens to almost everyone, should not be a cause for concern.
And, although researchers proposed more than 100 years ago that viruses or harmful microbes could contribute to Alzheimer’s disease, no pathogen has been consistently linked to the disease.
The researchers propose that these two studies illustrate the potential impact that infections can have on brain health and neurodegeneration in general. However, they add that independent studies are needed to test their findings and resulting hypotheses.
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