Scientists at Trinity College Dublin and other institutions worldwide are investigating the potential link between certain viruses, bacteria, and dementia, as well as how an anti-inflammatory lifestyle may reduce the risk of pathogens damaging the brain. Neuroscientist Colm Cunningham has spent years studying the connection between episodes of delirium, often triggered by infections, and the onset of dementia.

Experts believe that there are many ways pathogens could cause dementia. One possible reason involves hit-and-run infections, such as SARS-CoV-2, which can invade organs and cause damage, leading to brain injury and an increased risk of dementia. Hit-and-stay infections, on the other hand, can assimilate within the body’s tissues for years, potentially awakening and invading the brain as the immune system weakens over time.

In some cases, multiple infections throughout a lifetime might cause a slow buildup of inflammation in the body, impacting brain function and possibly leading to delirium episodes, an early sign of cognitive decline. Yvonne Nolan, a professor in anatomy and neuroscience at University College Cork, noted that infectious agents have been found in the brains of Alzheimer’s patients, potentially exacerbating brain inflammation.

A clinical trial at Columbia University Medical Center is currently investigating whether a herpes antiviral drug, valacyclovir, can slow Alzheimer’s progression in patients with early-stage disease. Biotech company Keystone Bio is designing drugs targeting the Porphyromonas gingivali bacteria to reduce brain inflammation. Nikki Schultek, who runs The Alzheimer’s Pathobiome Initiative, has discovered that in some cases, treating underlying infections can reverse dementia symptoms.

Cunningham warns that earlier interventions may be necessary for many patients, as brain damage could be too advanced by the time of dementia diagnosis. He believes that the increasing evidence of microbial involvement in dementia supports offering people more preventative vaccines against various viruses in mid-life, such as flu vaccinations or shingles vaccines.

As a funded investigator with APC Microbiome Ireland, Nolan is examining the relationship between the gut microbiome and the risk of developing dementia later in life. Research is looking into whether infections, lifestyle factors, or interventions like exercise and prebiotics can reduce inflammation, potentially preventing cognitive decline.

Collaborating with scientists at King’s College London, Nolan is also investigating how the gut microbiome and brain respond to exercise in middle age. This project aims to determine if regular exercise during one’s 40s, 50s, and 60s can lead to positive changes in microbiome composition, ultimately protecting against dementia in later years.

Nolan emphasised that Alzheimer’s is heavily influenced by lifestyle and environmental factors, suggesting that modifying the gut microbiota through diet, exercise, or prebiotics might help tackle the disease or slow its progression.