How Do Infections Affect Brain Disorders and Mental Health?

What you need to know

• Infections can play a role in the development of various brain disorders and mental health conditions.
• Recent studies have found links between viral infections and neurodegenerative diseases like Alzheimer’s.
• Pandemics, such as COVID-19, can significantly impact mental health on a population level.
• Vaccines and antiviral treatments may help prevent or reduce the risk of some neuropsychiatric disorders.

The connection between infections and brain disorders

For over a century, scientists have suspected that some brain disorders might be related to infections. This idea gained traction in 1905 when researchers discovered that neurosyphilis, a severe neurological condition, was caused by a bacterial infection. Since then, our understanding of how infections can affect the brain and mental health has grown significantly.

Recent studies have shed new light on the complex relationship between infections and neuropsychiatric disorders. These findings are particularly relevant in the context of the COVID-19 pandemic, which has been associated with an increased risk of various neurological and psychiatric conditions.

Herpesviruses and Alzheimer’s disease

One area of research that has gained attention is the potential link between herpesviruses and Alzheimer’s disease. Herpesviruses are a family of viruses that include common infections like cold sores and chickenpox. While the idea of a connection between these viruses and Alzheimer’s has been around for years, recent studies have provided more substantial evidence to support this association.

Several key findings support the link between herpesviruses and Alzheimer’s:

1. Studies of human brain tissue after death have found higher rates of herpesvirus infections in people with Alzheimer’s disease.
2. Animal studies suggest that the brain’s response to viral infections, including the production of amyloid-beta (a protein associated with Alzheimer’s), may initially be protective but can become harmful over time.
3. Genetic studies have identified interactions between genes associated with Alzheimer’s risk and herpesvirus infections.

These findings suggest that herpesviruses might play a role in the development of Alzheimer’s disease in some people. However, it’s important to note that this doesn’t mean all cases of Alzheimer’s are caused by herpesvirus infections, or that everyone infected with a herpesvirus will develop Alzheimer’s.

Infections and neurodegenerative diseases

Another recent study examined the relationship between various infections and several neurodegenerative diseases, including Alzheimer’s, Parkinson’s disease, and multiple sclerosis. The researchers analyzed data from large national databases in Finland and the UK to look for associations between infectious disease exposures and the later development of these brain disorders.

Some key findings from this study include:

1. Influenza infections with pneumonia were associated with an increased risk of five out of six neurodegenerative disorders studied.
2. Other infections linked to increased risk included meningitis, viral encephalitis (brain inflammation), and infections caused by herpesviruses and human papillomaviruses.
3. Some of these associations were significant even 5 to 15 years before the diagnosis of the neurodegenerative disorder, suggesting a long-term effect.

These results highlight the potential long-term impacts of infections on brain health. They also suggest that preventing or effectively treating certain infections might help reduce the risk of some neurodegenerative diseases.

Mental health during epidemics

The COVID-19 pandemic has brought renewed attention to the impact of large-scale disease outbreaks on mental health. A comprehensive review of studies from various epidemics, including COVID-19, SARS, and others, revealed some striking findings:

1. During epidemic periods, about 20% of the general population experienced moderate depression, and 30% experienced moderate anxiety.
2. Higher rates of mental health problems were seen in people with diagnosed mental disorders, those with confirmed or suspected infections, and those with infected family members or colleagues.
3. Risk factors for mental health problems during epidemics included being female, older than 40, unmarried, having a lower education level, and engaging in behaviors like smoking or drinking alcohol.
4. Protective factors included good social support and regular exercise.

These findings emphasize the widespread impact of epidemics on mental health and the importance of addressing these issues as part of the overall response to disease outbreaks.

Implications for prevention and treatment

The growing evidence linking infections to neuropsychiatric disorders opens up new possibilities for prevention and treatment:

1. Vaccines: Existing vaccines for viruses like influenza, herpes zoster (shingles), and human papillomavirus might help reduce the risk of some neurodegenerative diseases. Developing new vaccines for other implicated viruses could provide additional protection.

2. Antiviral treatments: Some researchers suggest that antiviral medications might be beneficial in treating or preventing conditions like Alzheimer’s disease, particularly if started early.

3. Early detection: Testing for exposure to certain viruses could become part of routine health screenings, especially for older adults or those at higher risk of neurodegenerative diseases.

4. Mental health support during epidemics: Recognizing the significant impact of disease outbreaks on mental health, it’s crucial to incorporate mental health support into epidemic response plans.

Conclusions

• Infections, particularly viral infections, may play a more significant role in brain disorders and mental health than previously recognized.
• Preventing and effectively treating certain infections could potentially reduce the risk of some neurodegenerative diseases.
• Large-scale disease outbreaks can have substantial impacts on population-level mental health, highlighting the need for comprehensive approaches to epidemic management.
• Further research is needed to fully understand the complex relationships between infections, genetics, environmental factors, and brain health.