Virus causing gut infections could play role in development of Alzheimer’s: Study

A virus that can cause infection in the gut and from there travel to the brain, could be important in the development of Alzheimer’s disease, according to a study.

Existing antiviral drugs may then be looked at for treating or preventing this form of Alzheimer’s disease, researchers, including those at the Arizona State University, US, said.

Most humans are thought to have been exposed to cytomegalovirus (HCMV), one of the nine viruses known to cause herpes (painful blisters on the skin), during the first few decades of their lives. The virus is usually transmitted through bodily fluids and spreads only when it is active.

Published in Alzheimer’s and Dementia: The Journal of the Alzheimer’s Association, the study found that in some people, the herpes-causing virus may remain active in the gut, from where it can travel to the brain via the vagus nerve, which connects the gut and the brain.

Once in the brain, the virus can alter the immune system and contribute to changes in cells associated with Alzheimer’s disease, the researchers explained.

The researchers noted that the herpes-causing virus is recognized by immune cells in the brain, called microglia, which activate a specific gene called ‘CD83.’

The virus could then contribute to biological changes in the brain, which are known to be involved in the development of Alzheimer’s disease — a neurodegenerative disorder that progressively deteriorates brain function, such as memory and cognitive abilities, as one ages.

“We think we’ve identified a biologically unique subtype of Alzheimer’s that may affect 25-45% of people with the disease,” said Ben Readhead, first author and research associate professor at Arizona State University.

“This subtype includes the hallmark amyloid plaques and tau tangles — microscopic brain abnormalities used for diagnosis — and features a distinct biological profile involving the virus, antibodies, and immune cells in the brain,” Readhead added.

For the study, the researchers analyzed spinal fluid from Alzheimer’s patients and found antibodies produced specifically in response to the herpes-causing virus. They also found evidence of infection in the intestines and brain tissue of these individuals caused by the same virus.

Furthermore, the team observed the herpes virus within the vagus nerve of the patients, suggesting this could be the pathway through which it travels to the brain.

In another group of Alzheimer’s patients, the researchers were able to replicate the association between the gut infection and CD83(+) microglia.

A previous study by the researchers conducted a post-mortem analysis of the brains of Alzheimer’s patients and found that these patients were more likely to harbor CD83(+) microglia specifically