When we think of dementia, we often link it to ageing or family history. But could something as common as a viral infection increase the risk? 

Recent research suggests that adenoviruses, which are known for causing colds and pink eye, might have unexpected effects on brain health.

Dementia affects over 55 million people worldwide, making it one of the biggest health challenges today. 

While we know that factors like high blood pressure, diabetes, and lifestyle choices can raise the risk, scientists are now looking into whether certain infections could also play a role. 

In this article, we’ll explore what researchers are discovering about the possible connection between adenovirus and dementia.

What is Dementia and why does it happen?

Dementia is a condition that affects how the brain works, making it harder for people to remember things, think clearly, and carry out daily activities. 

It happens when brain cells (neurons) are damaged, preventing them from sending and receiving messages properly. The brain and nervous system control movement, memory, and thinking, so when neurons are lost, these functions become impaired.

The most common type of dementia is Alzheimer’s disease, which accounts for about 60–70% of cases. According to experts, dementia is a long-term and irreversible condition that affects multiple areas of thinking and memory.¹ It can also cause personality changes, making some people more emotional or easily confused.

Dementia is a growing global concern. The World Health Organization (WHO) reports that more than 60% living in low- and middle-income countries are affected by the condition. Every year, about 10 million new cases are diagnosed.²

Many factors increase the risk of dementia. Age is the biggest one, while everyone loses some brain cells as they grow older, people with dementia experience a much greater loss.³

 Other risk factors include high blood pressure, diabetes, obesity, smoking, excessive alcohol use, lack of exercise, social isolation, and depression.³

In the UK alone, nearly 982,000 people are currently living with dementia, and this number is expected to rise to 1.4 million by 2040.³

Forms of dementia

Dementia comes in different types, depending on its cause. 

The most common type is Alzheimer’s disease (AD), which affects up to five million Americans aged 65 and older. It happens when harmful proteins build up in the brain, forming amyloid plaques and tau tangles, which damage brain cells and lead to memory loss.²

Another type is frontotemporal dementia (FTD), a rare condition that mostly affects people under 60. It occurs when certain proteins, tau and TDP-43, build up in the brain, affecting behaviour, speech, and decision-making.

Lewy body dementia (LBD) is caused by clumps of a protein called alpha-synuclein, known as Lewy bodies. People with this type of dementia often have memory problems, confusion, hallucinations, and movement difficulties.

Vascular dementia happens when the brain doesn’t get enough blood and oxygen due to problems like strokes or blocked blood vessels. This damages brain cells and affects thinking, memory, and problem-solving. Mixed dementia is when a person has more than one type, such as Alzheimer’s and vascular dementia. Studies show that most people over 80 likely have mixed dementia.⁴

Some less common types include Limbic-Predominant Age-Related TDP-43 Encephalopathy (LATE), which has symptoms similar to Alzheimer’s, and dementia linked to conditions such as HIV/AIDS, Parkinson’s disease, and Huntington’s disease.⁵

Causes of dementia

Certain infections may increase a person’s risk of developing dementia. Microorganisms such as bacteria, fungi, viruses, and parasites like Toxocara have been linked to the condition. Among these, viruses are the most common infectious cause.

Viruses spread in different ways. Some, like those carried in droplets or aerosols, enter the body through the nose, mouth, or eyes. 

Others, like those transmitted by insect bites, enter directly into the bloodstream. Once inside the body, viruses attach to specific cells, allowing them to invade and multiply. They first replicate in areas like the lymph nodes before spreading further, sometimes reaching the brain.¹

Can adenovirus affect the brain?

Adenoviruses are a group of viruses known for causing infections, mainly in the respiratory and digestive systems. They were first identified in 1953 by Wallace Rowe while studying tissues from children's adenoids (a part of the throat). His research showed that adenoviruses could infect and damage human cells.

Most adenovirus infections cause mild illnesses like the common cold, but in some cases, they can lead to more serious conditions such as pneumonia.⁵ 

While these viruses are not commonly linked to brain diseases, some studies suggest that viral infections, including adenoviruses, may play a role in neurological conditions. 

Viral infections can trigger inflammation, which may contribute to long-term damage to the brain. This has raised questions about whether adenoviruses could be linked to neurodegenerative diseases like dementia.

Further research is needed to understand if and how adenoviruses might impact brain health.⁵

Exploring the link between Adenoviruses and neurological disorders

Some studies suggest that adenoviruses could influence brain function in unexpected ways. For example, research on Adenovirus 36 (Ad36) has shown that it may impact blood sugar regulation and cognitive function. 

In a study using a mouse model of Alzheimer’s disease (AD), Ad36 infection improved blood sugar control and slowed cognitive decline compared to uninfected mice. 

Another study found that adenovirus-delivered insulin-like growth factor 1 (IGF-1) helped protect against cognitive decline in diabetic mice. These findings raise questions about whether certain viruses could play a role in both brain diseases and their potential treatment. However, more research is needed to fully understand these effects.^6,7

Potential role of Adenoviruses in future treatments

If a stronger link between viral infections and neurological disorders is established, it could open new possibilities for treatment. Researchers are exploring the use of adenoviruses in therapies for conditions like brain cancers, neurodegenerative diseases, and genetic disorders. 

Some adenoviruses, such as Ad36, might have neuroprotective effects, meaning they could help slow or prevent cognitive decline in diseases like Alzheimer’s.

 In gene therapy, adenoviruses are also being tested as a way to deliver beneficial proteins, such as IGF-1, to protect brain function. While these approaches show promise, more research is needed to determine their safety and effectiveness.^7,10

Summary

There is still a lot to learn about whether viral infections, like adenovirus, play a direct role in causing Alzheimer’s disease (AD). 

Some research suggests that certain adenoviruses might help protect against memory loss, especially in people with conditions like diabetes. 

At the same time, adenoviruses can infect the brain and may contribute to neurological problems. More studies are needed to fully understand how adenoviruses interact with brain cells and their possible link to Alzheimer’s and other neurodegenerative diseases.