Can Alzheimer's Be Caused By Viruses?

A Silent Foe

Since its discovery in 1906, Alzheimer's has been the most common form of dementia in most countries around the world. In fact, within the United States, 10% of people aged 65 and older have Alzheimer’s! 

Yet, as widespread as this disease is, and as devastating as its effects are, we have only relatively recently understood what causes Alzheimer’s: That answer lies on the amyloid-beta and tau molecules within our very brains which play a role in hurting or damaging our brain cells, without which we cannot lose cognitive functions, leading to dementia.

What We Know

The current established understanding surrounding the causes of Alzheimer's is probably due to a mix of genetic factors and lifestyle factors. 

For example, with regards to the amyloid-beta molecule which forms entangles in the brain, Rudolph Tanzi, director of the McCance Center for Brain Health at Harvard-affiliated Massachusetts General Hospital, has shown that people with a gene that increases their level of amyloid-beta have a higher chance of developing Alzheimer's at a young age. 

Elsewhere, individuals who inherit two detrimental copies of the APOE4 gene aren’t able to clear amyloid-beta molecules within their brain as effectively, rendering them at even greater risks of developing Alzheimer's in their life.

According to the established research, both amyloid-beta plaques and tau tangles often trigger inflammation in the brain, which is termed as neuroinflammation. When this happens, the brain's own immune system cells fight to heal injury, but in doing so this can cause even more injury and thus more neuroinflammation — a vicious cycle that ultimately causes most of the death of neurons. 

What’s This Mean?

Well, many bacteria and viruses can also trigger neuroinflammation when they invade our body. 

Some microbes can infect the brain and they’re extremely difficult to be completely eliminated by the brain's immune system. These microbes could then cause long-term, low-grade neuroinflammation. 

Worse still, even infections in other parts of the body, or other causes of inflammation beyond the brain, can trigger hormones and signals that reach the brain, potentially triggering neuroinflammation.

During an infection, amyloid-beta is deposited in the brain to form a web that entraps invading microbes. This is good because it helps to protect our brain from infection. However, as mentioned above, the amyloid-beta also damages neurons which is one of the main pathways leading to dementia. The constant deposition of amyloid-beta can also lead to tau tangles which further damages neuron health.

FYI: We know this much because of studies conducted on the brains of rodents and other animals that were infected with microbes. Moreover, evidence also comes from studies showing that the risk of developing Alzheimer's is significantly higher in people who previously experienced a severe infection. 

Some suspected viruses that increase one’s chance of Alzheimer’s are the herpes simplex virus 1 and 2, the varicella-zoster virus (which causes chickenpox), and worst of all, COVID-19, otherwise formally known as SARS-CoV-2.

What Can We Do Then?

While genetic factors and unknown microbial assailants can have an impact, we can retain control by practicing lifestyle adjustments that reduce our risk of developing the disease. 

The theory that microbes may trigger Alzheimer's is still not yet fully unproven and accepted, but the evidence does seem to be growing stronger.

• Sleep at least seven hours a night to let your brain flush out waste material and toxins (including amyloid-beta!) 

• Use stress reduction technique e.g. go out with your friends; cells in the brain may make more amyloid and undergo more inflammation under stress

• Exercise and learn new skills to promote the birth of new brain cells

• Eat a healthy diet as unhealthy junk food can promote inflammation

• Get immunizations to reduce the risk of serious infections

Reference List‌

Bruno, F., Paolo Abondio, Bruno, R., Leognano Ceraudo, Paparazzo, E., Citrigno, L., Donata Luiselli, Bruni, A.C., Passarino, G., Colao, R., Maletta, R. and Montesanto, A. (2023). Alzheimer’s disease as a viral disease: Revisiting the infectious hypothesis. Ageing Research Reviews, 91, pp.102068–102068. doi:https://doi.org/10.1016/j.arr.2023.102068.

Eisenstein, M. (2025). Do infections have a role in Alzheimer’s disease? Nature, [online] 640(8059), pp.S8–S10. doi:https://doi.org/10.1038/d41586-025-01104-0.

Komaroff, A.L. (2025). Are some cases of Alzheimer’s disease caused by infection? - Harvard Health. [online] Harvard Health. Available at: https://www.health.harvard.edu/mind-and-mood/are-some-cases-of-alzheimers-disease-caused-by-infection.

National Institutes of Health (NIH). (2023). Links found between viruses and neurodegenerative diseases. [online] Available at: https://www.nih.gov/news-events/nih-research-matters/links-found-between-viruses-neurodegenerative-diseases.

www.ox.ac.uk. (n.d.). Viral role in Alzheimer’s Disease discovered | University of Oxford. [online] Available at: https://www.ox.ac.uk/news/2022-08-02-viral-role-alzheimers-disease-discovered.