Viral Infections Linked to Increased Risk of Neurodegenerative Diseases
Growing evidence suggests that viral infections can have long-lasting consequences, possibly contributing to the development of brain disorders like Alzheimer’s, Parkinson’s, and ALS years after the initial illness.
A large-scale study in 2023, analyzing nearly half a million medical records, revealed a considerably higher risk of neurodegenerative diseases in individuals who had experienced severe viral infections such as encephalitis or pneumonia.
Researchers identified 22 distinct connections between viral infections and conditions including Alzheimer’s, Parkinson’s, dementia, and ALS. Notably, individuals treated for viral encephalitis – inflammation of the brain – were 31 times more likely to develop Alzheimer’s disease compared to those without the infection. This translated to approximately 6% of cases (24 out of 406) developing Alzheimer’s.
Hospitalization for pneumonia following the flu was also associated with an increased risk of Alzheimer’s, Parkinson’s, and ALS. Furthermore, infections of the gut, meningitis, and the varicella-zoster virus (responsible for chickenpox and shingles) were also linked to brain diseases. The impact of these infections could be measured for up to 15 years after the initial illness, and no protective effect from any virus was observed.
How Viruses Impact the Brain
Approximately 80% of the viruses studied are neurotropic, meaning they can cross the blood-brain barrier and directly impact brain cells.
The researchers highlight the availability of vaccines for some of these viruses - including flu, pneumonia, and shingles - which, while not preventing all infections, can significantly reduce the risk of hospitalization and potentially lower the chances of developing brain disorders later in life.
While this study is observational and cannot definitively prove a causal relationship, its findings align with previous research, such as a 2022 study linking the Epstein-Barr virus to a 32-fold increase in the risk of multiple sclerosis.
The researchers conclude that their results reinforce the idea that viral infections and inflammation within the nervous system represent a common and potentially preventable risk factor for neurodegenerative diseases.
