Cold sore virus found to invade brain cells, raising Alzheimer's concerns

The common cold sore virus, known as herpes simplex virus type 1 (HSV-1), has shown the potential to invade the brain and increase the risk of developing Alzheimer’s disease. The virus usually resides dormant in the nervous system but can reactivate, especially when the immune system weakens. Research suggests that HSV-1 may travel to the brain through the olfactory nerve or the trigeminal nerve, which connects the face to the brainstem. Once in the brain, the virus can trigger inflammation and immune responses that may lead to damage and the accumulation of amyloid plaques, a hallmark of Alzheimer’s disease.


The inflammatory response to HSV-1 might activate microglial cells, immune cells in the brain that can release harmful substances when overstimulated. These processes can damage neurons and increase the production of beta-amyloid, a protein linked to Alzheimer's. Studies have shown that individuals with genetic risk factors, such as the APOE4 gene, are more vulnerable to these viral effects. Research indicates that antiviral treatments could potentially reduce Alzheimer's risk, emphasizing the importance of managing HSV-1 infections to minimize long-term neurological consequences.

CU Anschutz researchers provide fresh perspectives on the long-term consequences of HSV-1 infection. Common cold sores are caused by the Herpes simplex virus type 1 (HSV-1), which can also spread to the central nervous system and specific brain regions. The findings of the study, which were released today in the Journal of Virology, are among the first to identify the way in which this widespread virus enters the brain, improving our knowledge of how HSV-1 may cause neurological disorders.

Christy Niemeyer, PhD, an assistant professor of neurology at the University of Colorado Anschutz Medical Campus and co-first and corresponding author, states, "This common virus has recently been implicated in neurodegenerative diseases, such as Alzheimer's disease, but no clear route of central nervous system invasion has been established."

Understanding how HSV-1 causes disease requires knowing how it can enter the brain and which parts of the brain are susceptible.

Charting the Brain's HSV-1 Pathway
Researchers also sought to ascertain if HSV-1 migrates randomly or to certain regions of the brain when it enters. They were able to map the virus's path through the brain and identify key areas that are in charge of numerous essential processes, including the brain stem, which regulates movement and sleep. The hypothalamus, a crucial hub for mood, hunger, sleep, and hormone regulation, as well as areas of the brain that generate serotonin and norepinephrine, were also shown to harbor HSV-1.

Despite the fact that HSV-1 does not cause severe encephalitis, it can still impact the functioning of some regions in the brain, " says Neimeyer.



Microglia's Function in HSV-1 Infection

Niemeyer and colleagues also demonstrate how HSV-1 affects microglia, which are important immune cells in the brain. They discovered that when microglia interacted with HSV-1, they were "inflamed." However, in certain areas of the brain, the inflamed microglia continued to exist even after the virus was eliminated.

"Determining the function of microglia offers valuable hints regarding the effects of HSV-1 infection and how it causes neurological disorders," Niemeyer explains. Chronic inflammation, a known cause of several neurological and neurodegenerative disorders, can result from continuously inflamed cells. This study provides valuable insights into the relationship between viruses and both the development of common neurological disorders and general brain health.

Precautions to be taken


According to Dr Kunal Bahrani, Clinical Director & HOD-Neurology, Marengo Asia Hospitals Faridabad, “You can take several precautions to minimize the risk of HSV-1 complications, including its potential impact on brain health. First, manage stress and maintain a strong immune system through a healthy lifestyle, as stress and a weak immune system can reactivate the virus. Regular exercise, a balanced diet, and adequate sleep are essential. If you are prone to cold sores, use antiviral creams or oral medication to reduce the severity and duration of outbreaks. Protecting your lips and skin from the sun can also help prevent flare-ups.”


Practicing good hygiene is crucial. Avoid direct contact with the sores of an infected person, and refrain from sharing personal items like towels, lip balms, or eating utensils. If you have a compromised immune system, consult your healthcare provider about preventive antiviral medications. People with genetic predispositions to Alzheimer’s or who have a history of severe cold sore outbreaks should consider regular medical check-ups to monitor neurological health. Early intervention and a proactive approach to controlling HSV-1 can reduce the risk of long-term complications.


Who is at high risk of common cold sore virus


Certain groups are at a higher risk of contracting and experiencing complications from the herpes simplex virus type 1 (HSV-1). Those with weakened immune systems, such as individuals undergoing chemotherapy, people with HIV/AIDS, or those taking immunosuppressive medications, are more likely to suffer from severe infections or frequent reactivations of the virus. Age is another factor; older adults, particularly those with genetic predispositions like the APOE4 allele, are more susceptible to HSV-1’s neurological impacts.


People who frequently experience cold sores are also at risk. Physical or emotional stress can trigger viral reactivation, making it essential for high-risk individuals to manage stress effectively. Additionally, those who suffer from chronic conditions like diabetes may experience complications due to immune system impairment. Children and healthcare workers have a higher likelihood of exposure and infection, with transmission often occurring through saliva or direct contact with an infected person’s sores.


Taking preventive measures, such as minimizing contact with individuals experiencing active cold sore outbreaks and practicing good hygiene, can reduce the chances of infection. If you belong to a high-risk group, consider discussing antiviral therapies with your doctor, especially if you experience recurrent or severe outbreaks, to lower the potential impact of the virus on overall health.