Common Virus May Cause a Type of Alzheimer’s

Researchers have discovered a link between a chronic gut infection caused by a common virus, known as cytomegalovirus (CMV), and the development of Alzheimer’s disease in some people. CMV occurs in most people during childhood, but after the initial infection, the virus usually remains dormant in the body for life.

In the study, the researchers had access to a range of donated organ tissues, including the colon, vagus nerve, brain and spinal fluid, from 101 body donors, 66 of whom had Alzheimer’s disease. This helped them study how the body’s systems interact with Alzheimer’s disease, which is often considered through a purely neurological lens. They traced the presence of CMV antibodies from donors’ intestines, to their spinal fluid, up to their brains and even discovered the virus itself lurking within the donors’ vagus nerves. This means CMV may have found a biological loophole where it can remain active long enough to travel to the gut-brain axis superhighway, known more officially as the vagus nerve. On arriving at the brain, the active virus has the potential to aggravate the immune system and contribute to the development of Alzheimer’s disease. The same patterns showed up when they repeated the study in a separate, independent cohort.

Human brain cell models provided further evidence of the virus’s involvement by increasing amyloid and phosphorylated tau protein production and contributing to neuron degeneration and death. Importantly, these links were found only in a very small subset of individuals with chronic intestinal CMV infection. Given that almost everyone comes into contact with CMV, simply being exposed to the virus is not always cause for concern.

“We think we found a biologically unique subtype of Alzheimer’s that may affect 25 percent to 45 percent of people with this disease,” biomedical scientist and lead author Ben Readhead from Arizona State University said. “This subtype of Alzheimer’s includes the hallmark amyloid plaques and tau tangles — microscopic brain abnormalities used for diagnosis — and features a distinct biological profile of virus, antibodies and immune cells in the brain.”

According to the researchers, this means antiviral drugs might be able to prevent some people from developing Alzheimer’s, especially if researchers can develop blood tests to quickly detect active CMV infection in the gut. Readhead and his team are working to develop such a blood test so the CMV infection can be treated with antivirals, and perhaps prevent patients from developing this type of Alzheimer’s.