A common virus may help trigger Alzheimer’s disease by chronically infecting the gut, a new study suggests.
A common virus may underlie Alzheimer’s disease, a new study shows PHOTO Shutterstock
HCMV is one of nine types of herpes viruses to which most people are exposed in the first decades of life. Unlike most herpes viruses, this one is not considered to be sexually transmitted, according to The Independent.
Researchers at the University of Arizona in the US found that the virus can persist in the gut and travel to the brain via the vagus nerve, which connects the two.
Once in the brain, it can trigger changes in the immune system associated with Alzheimer’s disease, according to the study published in the journal Alzheimer’s & Dementia.
“We believe we have identified a biologically unique subtype of Alzheimer’s disease that may affect 25-45% of people with the disease”said Ben Readhead, co-author of the study.
How the virus manifests itself
If the findings are validated by further research, existing antiviral drugs could be tested to treat or prevent this form of Alzheimer’s. This may be supported by a blood test under development that could identify patients with an active HCMV infection.
In some people who develop a chronic intestinal infection caused by HCMV, the virus could reach the brain either through the bloodstream or the vagus nerve.
Once in the brain, the virus causes immune cells called microglia to turn on the expression of a gene called CD83, which has been linked in a previous study to Alzheimer’s disease.
Although microglia initially provide protection against infection, their sustained activity can lead to chronic inflammation and neuronal damage – implicated in the progression of diseases such as Alzheimer’s.
Previous studies
A previous study, published last year in the journal Nature, showed that post-mortem brains of research participants who had Alzheimer’s were more likely to contain CD83 microglia compared to those of people without the neurological condition.
The same study identified an antibody in their intestines, suggesting that an infection may have contributed to this form of Alzheimer’s.
How the study was conducted
In the latest study, the scientists examined the spinal fluid of the same individuals and found that the antibodies were specific against HCMV. They also found HCMV in the vagus nerve, indicating the route by which the virus reaches the brain.
The researchers used brain cell models grown in the lab to show that the virus can induce Alzheimer’s-related changes, such as the production of amyloid and tau proteins, which are associated with nerve cell death.
However, the researchers stress that further independent studies are needed to confirm the new findings.
