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Cold sores are a common problem, and people everywhere get them. If you have not had them, you probably know someone who has. [Ed. Note: They should not be confused with canker sores. See “Canker sores not contagious.”]

They are caused by a virus known as herpes simplex, and about 90% of people are infected with it. Most of us pick up the virus in childhood and recover from the cold sores without any treatment. But the virus remains dormant in our bodies in nerve cells in the skin, as does the chicken pox virus.

There is no way to get rid of the virus, and it can later be reactivated by various factors, such as stress, fatigue, exposure to strong sunlight or wind, and a weakening of the immune system — much like the chicken pox virus, which causes shingles when reactivated.

A precursor to Alzheimer’s?

A recent study conducted by a multidisciplinary team at Tufts University, published in May 2020 in the journal Science Advances, provides strong evidence that the herpes simplex virus may be responsible for creating the conditions in the brain that lead to Alzheimer’s disease.

Three decades earlier, scientists had already found evidence of a connection between the virus and Alzheimer’s. As early as 1991, scientists discovered that the virus can make its way from the nerve cells in the skin all the way to the brain, and many elderly people do indeed have the virus in their brain.

In 1997, it was shown that elderly people who have the virus in their brain and also have the APOE4 gene [the gene that increases risk of early-onset Alzheimer’s up to five times] are 12 times more likely to get Alzheimer’s than those without the virus and without the gene.

Associated with plaques, tangles

More recently, in 2007, it was found that the presence of the virus in the brain is associated with an increase in the formation of beta-amyloid plaques, which accumulate around brain cells in Alzheimer’s patients.

And in 2009, a research team at the University of Manchester in the U.K. demonstrated that the virus is responsible for the development of the tau tangles within brain cells that are also associated with Alzheimer’s.

An earlier British study, published in 2008, showed that there was a high level of the virus’s DNA within the beta-amyloid plaques extracted posthumously from the brains of Alzheimer’s patients. Thus, over the years, evidence has accumulated that points to the cold sore virus as one of the major causes of various dementias.

It is not clear exactly how this virus causes the conditions that lead to dementia. Scientists think that the virus makes its way toward the brain as we get older and our immune system gradually weakens.

When it reaches the brain, it lies dormant until it is reactivated by some triggering event, such as stress or inflammation in the brain caused by some other infection.

Reactivation of the virus damages the infected brain cells and produces inflammation. Repeated reactivation causes the damage to pile up and become irreversible.

The study published in May last year demonstrated that in artificially created human brain tissue in the lab, large beta-amyloid plaque-like formations developed just three days after infection with the herpes simplex virus, accompanied by high levels of inflammation and other forms of cell damage.

Potential route to a cure

The researchers also tested the effect of antiviral medication and found that antivirals help to reduce the damage to cells caused by the virus.

The role of antiviral drugs had already been studied using human subjects. A 2011 British study conducted in the lab showed that three anti-herpes antiviral drugs on the market are effective in greatly reducing the accumulation of beta-amyloid plaques and tau tangles in infected cells.

Researchers are now looking at ways to treat dementia with antiviral medication early on and perhaps even prevent the onset of the disease.

Dr. Alfred is a Certified Dementia Practitioner and the CEO of AlfredHouse Assisted Living.