These are the two common viruses whose infection can trigger Alzheimer's years later

These are the two common viruses whose infection can trigger Alzheimer’s years later

Alzheimer’s disease can start unnoticed, camouflaged among the memory problems of the elderly. The reasons that lead some people to develop the most frequent neurodegenerative disease in the elderly in Spain and others are not largely unknown. However, researchers at Oxford University and their colleagues at Tufts have discovered a link between Alzheimer’s and varicella-zoster virus (VZV), which in turn can activate the herpes simplex virus (HSV) and trigger the disease.

One of the variants of the herpes virus, HSV-1, tends to remain inert between brain neurons. If activated, however, it prompts the accumulation of tau proteins and amyloid betaand interferes with neural function, all symptoms of Alzheimer’s. “This suggests an activation pathway in Alzheimer’s disease whereby a VZV infection causes an inflammatory response that in turn arouses HSV-1 in the brain,” explains Dr. Dana Cairns, one of the authors of the work. published in the Journal of Alzheimer’s Disease.

“We know that there is a correlation between the HSV-1 and Alzheimer’s disease, and involvement of VZV was also suggested. What we didn’t know was the sequence of events created by viruses to trigger the processes that will lead to disease,” explains Dr. David Kaplan, Professor of Biomedical Engineering at the Tufts University School of Engineering. As he recalls, the World Health Organization (WHO) estimates that 3.7 billion people under the age of 50 worldwide have HSV-1, the virus herpes labialis.

The varicella-zoster virus is also extremely common: before the age of 20, 95% of the human population will have been exposed to it. The most common manifestation is chickenpox when vaccination against that disease has not been completed, but it can also remain inert for years and reappear as Herpes zoster. It is estimated that one in three people can suffer from this type of rash popularly known as ‘shingles‘, characterized by reddening of the skin in bands and the appearance of nodules and blisters.

How do viruses wake up?

To understand the cause-and-effect relationship between viruses and Alzheimer’s, the researchers recreated environments similar to the human brain using protein and collagen sponges, arranged in donut-shaped structures six millimeters in diameter. They populated them with neural stem cells that were allowed to grow until they began to pass signals to each other as they would in a real brain. Some even formed glial cellswhich help neurons function and stay alive.

These neurons can be infected with VZV, the researchers noted, but that alone is not enough to form the amyloid beta and tau proteins found in brain plaques in Alzheimer’s patients. But if these cells already contained dormant HSV-1, the interaction with the new virus triggered the neurodegenerative process. In these cases, it was observed an increase in cytokine productionproteins secreted by the immune system that provoke an important inflammatory response.

Repeated cycles of herpes virus reactivation would accelerate the accumulation of cognitive and neuronal damage, the authors explain, “Risk factors such as head trauma, obesity, or alcohol use may contribute to the reappearance of HSV-1 at the neuronal level,” warns Cairns. On the other hand, the varicella vaccination it is related to a lower risk of senile dementia, which could be indicative of this mechanism. Lastly, Covid-19 infection has been shown to be capable of reactivating both VZV and HSV-1, which is why they urge monitoring of its impact on Alzheimer’s in the future.

Source: Elespanol

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