Infection with the virus that’s the main cause of cold sores may double a person’s risk of developing dementia, according to a new study. Adding to growing evidence of a link between the two, further research is needed to investigate whether anti-herpes treatment reduces the risk and may open the door to developing new vaccines.
Herpes simplex virus (HSV) is a common, lifelong infection that’s treatable but not curable. It’s estimated that, globally, around 67% of people under 50 have herpes simplex virus type 1 (HSV-1) infection, the main cause of oral herpes or cold sores, and around 13% have herpes simplex virus type 2 (HSV-2) infection, the main cause of genital herpes.
Another prevalent condition, dementia, is on the rise, with worldwide cases expected to reach 78 million in 2030. Although the exact cause of Alzheimer’s disease (AD), the most common form of dementia, is not yet known, growing evidence from large population-based studies has suggested that HSV infection plays a role in the development of AD or dementia. Now, a new study by researchers at Uppsala University in Sweden has examined the link between HSV infection and dementia risk.
“What’s special about this particular study is that the participants are roughly the same age, which makes the results even more reliable since age differences, which are otherwise linked to the development of dementia, cannot confuse the results,” said Erika Vestin, the study’s lead author.
The study was conducted with 1,002 dementia-free 70-year-olds who were followed for 15 years. Blood samples were analyzed to detect anti-HSV and anti-HSV-1 IgG antibodies, anti-cytomegalovirus (CMV) IgG, anti-HSV IgM antibodies, and anti-HSV and anti-CMV IgG levels.
Immunoglobulin M (IgM) is the first antibody secreted by the adaptive immune system in response to the body’s first exposure to a foreign antigen. Immunoglobulin G (IgG) is the most common type of antibody found in the blood that binds to pathogens like viruses and bacteria to protect against infection. HSV infection – or HSV carriership – can be demonstrated by the presence of IgG in blood, with IgM detection and higher IgG levels reflecting frequent reactivation. CMV is another herpesvirus whose association with the risk of AD or dementia has been studied.
Of the participants, over the course of the study, 7% developed all-cause dementia and 4% developed AD. The study found 82% of participants were anti-HSV IgG carriers, of whom 6% received anti-herpesvirus treatment.
The researchers found that anti-HSV IgG positivity was associated with a more than doubled risk of dementia. No significant association was found with AD, particularly, although the hazard ratio – a measure of how often a particular event happens in one group compared to another – was of the same magnitude as for dementia.
Anti-HSV IgM and anti-CMV IgG prevalence, anti-herpesvirus treatment, and anti-HSV and anti-CMV levels were not associated with AD or dementia, nor were interactions between anti-HSV IgG prevalence and the presence of apolipoprotein e4 (APOE e4), a protein implicated in Alzheimer’s disease, or anti-CMV IgG.
The lack of association between the anti-HSV IgG level and AD or dementia, together with the association between anti-HSV IGG prevalence and dementia, indicates that the presence, rather than the level, of IgG is indicative of a dementia risk, say the researchers.
“It is exciting that the results confirm previous studies,” Vestin said. “More and more evidence is emerging from studies that, like our findings, point to the herpes simplex virus as a risk factor for dementia.”
The researchers note that the low incidence of AD may have impaired the statistical power to detect associations. While HSV appeared not to interact with CMV or APOE e4, further studies with more power are needed to examine potential interactions. Randomized controlled trials, rather than observational studies, are also needed to investigate whether already known drugs used to treat HSV can reduce the risk of dementia and the possibility of developing new vaccines.
“The results may drive dementia research further towards treating the illness at an early stage using common anti-herpes virus drugs, or preventing the disease before it occurs,” said Vestin.
The study was published in the Journal of Alzheimer’s Disease.
Source: Uppsala University
