Herpes simplex virus type1 (HSV-1 or oral herpes) causes cold sores, and, less commonly than type 2, it can also cause genital herpes. Herpes zoster is the virus that causes chicken pox and shingles, and is not a suspect here. All herpes viruses are widespread in human populations.
According to a controversial hypothesis, sporadic but not genetic Alzheimer’s may be a long-term consequence of early HSV-1 infection. Support comes from a study from Taiwan, published in 2018, looking at 33,000 subjects of whom 8000 had been infected with HSV-1. The 20-year risk of developing dementia was 2.5 times as high in those who had been infected. Anti-viral treatment (Acyclovir and others) reduced that risk.
Now, more support comes from a new 3D model of Alzheimer’s. Think of cell culture using human neural stem cells. Infecting them with HSV-1 led to amyloid plaques and tau aggregates, the classic pathological hallmarks of Alzheimer’s. Critics pointed out that the amyloid plaques “did not meet standard specifications.” An earlier cell culture study published in 2014 used a different model and had similar results.
Importantly, these studies suggest that herpes is an important cause of Alzheimer’s, rather that just an innocent bystander. Where we go from here is not clear but stay tuned.
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