Researchers link common herpes virus to a specific form of Alzheimer's disease

Study suggests cytomegalovirus may travel via the vagus nerve to the brain, contributing to Alzheimer's progression.

 Walk to end Alzheimer's at Big Spring International Park. (photo credit: Katssoup. Via Shutterstock)
Walk to end Alzheimer's at Big Spring International Park.
(photo credit: Katssoup. Via Shutterstock)

A new study published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association has identified a possible link between cytomegalovirus (HCMV), a common virus, and Alzheimer's disease. Researchers from Arizona State University and the Banner Alzheimer's Institute have found that HCMV was present in up to 45% of Alzheimer's cases studied. According to a report by The Sun, scientists now believe that HCMV might play a role in up to 45% of all Alzheimer's cases.

"We think we found a biologically unique subtype of Alzheimer's that may affect 25% to 45% of people with this disease," said Dr. Ben Readhead, co-first author of the study, according to The Sun. This subtype is characterized by a distinct viral footprint and the presence of virus-specific antibodies and immune cells that stir up inflammation.

The study suggests that in some individuals, HCMV remains active in the intestine and may reach the brain through the vagus nerve, which connects the gut and the brain. According to Science Daily, the active virus can travel to the brain via the vagus nerve, and traces of the virus have been found in the nerve, suggesting this transmission pathway. The vagus nerve, described as the "superhighway" of the body between the intestine and the brain, may serve as the route for HCMV to reach the brain, reported 20 Minutos.

When HCMV reaches the brain, it may disrupt immune responses and trigger reactions that lead to the characteristic changes of Alzheimer's disease, such as the formation of amyloid plaques and tau tangles. Experiments showed that exposing human brain cell models to HCMV led to increased production of amyloid and phosphorylated tau proteins, which are linked to Alzheimer's disease, and caused neuronal degeneration, according to ANSA [https://www.ansa.it/canale_saluteebenessere/notizie/medicina/2024/12/19/alzheimer-alcuni-casi-legati-a-citomegalovirus-nellintestino_3572e422-92f2-4321-a514-118ac28fdc69.html].

Scientists identified a link between specific immune cells, known as CD83(+) microglia, and elevated levels of an antibody called immunoglobulin G4 (IgG4) in the colon, vagus nerve, and brain tissue of Alzheimer's patients, according to Science Daily. The association was observed in 47% of Alzheimer's patients compared to 25% of healthy individuals, indicating a potential systemic rather than purely neurological origin of the condition.

Researchers suggested that some individuals with chronic intestinal HCMV infections could be treated with antiviral medications to potentially prevent the development of Alzheimer's disease, as reported by 20 Minutos. They propose that existing antiviral drugs could potentially treat or prevent this form of Alzheimer's disease by targeting the viral infection pathway associated with HCMV, according to ANSA.

The team is developing a blood test to identify individuals with active HCMV infection, which could help assess the use of antiviral drugs in treating or preventing this form of Alzheimer's disease, according to The Sun. "We're excited about the chance to have researchers test our findings in ways that make a difference in the study, subtyping, treatment, and prevention of Alzheimer's disease," said Dr. Eric Reiman, senior author and Executive Director of Banner Alzheimer's Institute, according to Science Daily.

Researchers emphasize that simple exposure to HCMV, which occurs in most people, should not be a cause for concern, according to Science Daily. HCMV spreads through bodily fluids such as saliva, and most people contract it during childhood without exhibiting symptoms, reported Al-Rai. HCMV is one of nine herpes viruses that most humans encounter, typically contracted through bodily fluids and often remaining dormant, as noted by Science Daily. While HCMV often remains dormant, it can become active under certain conditions.

By age 80, approximately 80% of individuals have antibodies to HCMV, highlighting the widespread nature of this infection among older adults, according to Gilmore Health News. Although scientists have suspected a role for microbes in Alzheimer's disease for over a century, no pathogen has been consistently linked to the condition until now, according to Science Daily.

Currently, there is no cure for Alzheimer's disease, and existing treatments primarily focus on symptomatic relief, as reported by 20 Minutos. Alzheimer's disease is the most common form of dementia and a leading cause of death, according to The Sun. The discovery opens the door to new possibilities for addressing Alzheimer's disease and could lead to new therapeutic approaches, noted Devdiscourse.


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The study demonstrates the potential impact that infections can have on brain health and neurodegeneration, as reported by The Sun. Independent studies are necessary to verify these findings and test the resulting hypotheses, as stated by Science Daily. "It was critically important for us to have access to different tissues from the same individuals. That allowed us to piece the research together," said Readhead, emphasizing the unique contributions of Arizona's Brain and Body Donation Program, according to Science Daily.

The research was a collaborative effort involving investigators from various institutions, including UMass Chan Medical School, Institute for Systems Biology, Rush University Medical Center, and Icahn School of Medicine at Mount Sinai, reported Science Daily. The researchers note that independent studies are required to confirm their findings, as mentioned by iefimerida.

The article was written with the assistance of a news analysis system.