Research continues to uncover new potential risk factors for Alzheimer's disease, with recent studies highlighting a common virus known as human cytomegalovirus (HCMV) as a possible contributor. HCMV is widespread, with about one-third of Americans showing antibodies by age 5, and half by age 40. In developing countries, the virus affects nearly 90% of the population. While often dormant, HCMV can establish itself in the gut and later migrate to the brain, potentially accelerating the production of amyloid and tau proteins associated with Alzheimer's.
HCMV remains a persistent presence in the human body, controlled but never fully eliminated by the immune system. This enduring presence means that the virus can reactivate, possibly leading to reinfection of the gut and migration to the brain. This potential journey is facilitated by the vagus nerve, which may play a critical role in the virus's progression from the gut to the brain.
Co-infections with other viruses could amplify HCMV's ability to infect the gut or brain. Researchers have noted that microglia, a type of immune cell, are linked with increased immunoglobulin G4 and HCMV in the gut, vagal nerve, and brain. This connection underscores HCMV's potential impact on neurological health.
“We are describing what is probably a pretty modest slice of Alzheimer’s disease, [and] we have not established that this infection and CD83(+) cause Alzheimer’s disease,” – Readhead
The study's findings suggest that HCMV could be a risk factor for Alzheimer's in certain individuals, possibly affecting them decades before symptoms appear. The weakened blood-brain barrier in some individuals might enable pathogens like HCMV to enter the brain, leading to conditions that mimic Alzheimer's disease. This can result in misdiagnoses since HCMV can present symptoms similar to those of Alzheimer's but are not identical.
One challenge in studying HCMV's role in Alzheimer's is that it can only be detected during post-mortem analyses, not in living individuals. This limitation makes it difficult to determine when exactly an individual might have been infected.
“It is hard to do in a human being because we don’t know when they [were] infected. We only find it in post-mortem analysis,” – Brian Balin
“Having said that, I think it’s pretty plausible that this process is somehow contributing to pathology.” – Readhead
“We don’t have direct evidence of that yet, but we do know that Alzheimer’s disease has a multi-decade preclinical course,” – Readhead
The potential link between HCMV and Alzheimer's is further complicated by its association with Alzheimer's disease-associated CD83(+) microglia. These immune cells, found in increased numbers in individuals with the virus, highlight a possible pathway through which HCMV could influence neurodegenerative processes.
In developing countries, where HCMV infection rates are significantly higher, understanding this virus's role in Alzheimer's could be crucial. As researchers continue to explore this connection, it underscores the importance of considering infectious agents as potential risk factors in the development of neurodegenerative diseases.
Leave a Reply