Test tube and mice research has found that herpes and other viruses speed up the development of neurodegenerative diseases like Alzheimer’s.
How Herpes Viruses Can Cause Amyloid Plaque Buildup
The study, published in the journal Nature Communications, found that when certain viruses come into contact with a person’s blood or other biological fluids, the viruses develop a protective layer of proteins around it. This coat of proteins, called the protein corona, not only makes the virus more infectious, it speeds up the formation of plaques associated with brain conditions like Alzheimer’s and other forms of dementia.
Conducted by researchers at Stockholm University and Karolinska Institutet, the study determined that respiratory syncytial virus (RSV) and herpes simplex virus type 1 (HSV-1) bind to beta-amyloid proteins that turn into hardened plaques in the brain and cause neuron death. Beta-amyloid plaques are a hallmark biomarker of Alzheimer’s disease.
Herpes and Alzheimer’s: What Past Research Has Shown
The idea that microbial infections like herpes cause neurodegenerative diseases cropped up in the 1950’s. Since then, several studies have linked the herpes simplex virus to the onset of Alzheimer’s disease.
A study from 2018 analyzed DNA and RNA in the brains of deceased Alzheimer’s patients, and instead of discovering any particular human genes, the researchers uncovered an abundance of genes related to two strains of the herpes virus — HHV-6A and HHV-7. Another found that herpes is linked to half of all Alzheimer’s cases.
Until now, the connection between viruses and amyloid plaques were not well understood. For the first time, this new study shows how some viruses can speed up the neurodegenerative decline and the progression of Alzheimer’s.
To test this, researchers took mice engineered to quickly develop amyloid plaques and infected some of them with HSV-1. Those infected with the herpes virus developed signs of Alzheimer’s within 48 hours. Uninfected mice took several months to develop the disease.
Herpes Is Too Common to Explain All Alzheimer’s Cases
The researchers caution that this does not confirm that herpes causes Alzheimer’s disease. It does explain why so many researchers have found a connection between the two.
The authors go on to explain that these herpes strains are so common, 90 percent of us are infected with the virus as children. For that reason, it’s very unlikely that herpes simplex 1 is the only mechanism at play.
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[Image Credit: E. Wikander/Azote/Stockholm University]