The herpes (simplex) virus remains in the human body for life once it infects a person. It usually stays dormant but becomes active and shows symptoms when immunity weakens. It has been discovered that in addition to causing sores around the genital area and lips, it can also induce conditions such as Alzheimer’s disease in the brain.
Researchers from Arizona State University (ASU) and the Banner Alzheimer's Institute noted on the 20th in the international journal of the Alzheimer's Association, Alzheimer’s & Dementia, that "when the herpes virus infects the gut, it is likely to later move to the brain and trigger Alzheimer’s disease." The Banner Alzheimer’s Institute collaborates with global pharmaceutical companies, including Eli Lilly and Roche, on Alzheimer's treatment research.
The herpes virus is extremely common, with over 70% of the global population being carriers. According to the World Health Organization (WHO), about 67% of the global population under 50 years old is infected with herpes type 1 around the mouth, while 13% are infected with type 2 in the genital area, and it is estimated that about 87.4% of these individuals remain undiagnosed.
The research team examined the brains of individuals who died from Alzheimer’s disease to study the association between Alzheimer’s and herpes infection. They conducted research by creating brain organoids (mini organs) that preserved the histological features and microenvironment from the post-mortem brains using immunohistochemistry (IHC).
As a result, the researchers found evidence of herpes infection in the brain organoids. The principle is that the herpes virus moves to the brain via the vagus nerve, an important highway connecting the gut and brain. The autonomic vagus nerve connects the brain to the gut, allowing communication between the gut nervous system and the brain. The researchers stated that this virus becomes active in the brain and induces the abnormal accumulation and intertwining of amyloid beta and tau proteins, known as causes of Alzheimer’s disease.
Ben Readhead, a professor of neurodegenerative diseases at Arizona State University-Banner Institute and the lead researcher of this study, said, "We have discovered a biologically unique subtype of Alzheimer’s disease that may affect 25% to 45% of Alzheimer’s patients," adding, "This subtype of Alzheimer’s showcases distinct biological linkages between amyloid beta clusters, tau tangles, and viral associations in the brain with antibodies and immune cells."
The brains of Alzheimer’s patients analyzed by the research team showed a higher presence of inflammation-related immune cells and gut viruses compared to those without a history of Alzheimer’s. It was found that cerebrospinal fluid included antibodies related to human cytomegalovirus (HCMV), corresponding to herpes type 5.
The research team reported that the potential impact of herpes virus infection on brain health and neurodegeneration is extensive and is conducting further research. They are currently developing a blood test to confirm whether antiviral drugs used as Alzheimer’s treatments are effective for the treatment and prevention of Alzheimer’s disease.
Reference material
Alzheimer’s & Dementia (2024), DOI: https://doi.org/10.1002/alz.14401