HSV Linked to Alzheimer Disease

Herpes simplex virus corneal epithelial involvement in a patient on systemic corticosteroids. Courtesy wikimediacommons. http://creativecommons.org/licenses/by/2.5/deed.en

Could the common herpes virus be associated with Alzheimer disease (AD)? A research group at Umea University, Sweden, thinks it is possible.

In a paper published in Alzheimer’s & Dementia, the scientists reported that positivity for anti-herpes simplex virus (HSV) immunoglobulin M (IgM)-a marker for reactivated herpes infection-almost doubles the risk for Alzheimer disease.¹ The mere presence of immunoglobulin G (IgG) antibodies toward herpes simplex did not affect the risk for AD in this study.

The investigators studied 3,432 people, about half women and half men, with an average age of 63. Of these individuals, 245 developed AD. Researchers examined serum samples over 11 years and compared the antibody presence to the incidence of AD.¹

A second study, also published by the same researchers in Alzheimer’s & Dementia, compared plasma samples from 360 people with AD to those taken from 360 age and gender-matched control subjects who did not have dementia.² Samples were analyzed for anti-HSV antibodies, including IgG and IgM. When looking at all of the cases, researchers did not find a statistically significant increase in the risk of AD associated with antibody presence. However, when they looked specifically at individuals who had plasma samples analyzed within 6.6 years of diagnosis, they measured a significant association between anti HSV IgG antibodies and AD, once again supporting a herpes-Alzheimer link.

According to lead investigator, Hugo Lövheim, "The most interesting thing about our results is the identification of a potentially treatable cause of at least some cases of the most common dementia disorder; as HSV can be treated with antiviral drugs like acyclovir.”

Lövheim adds: "As HSV is always carried lifelong after the primary infection, presence of IgG should be interpreted as carriage of the virus, and IgM as reactivation. Almost all people with IgM antibodies also had IgG antibodies, ie, IgM was in almost all cases a sign of reactivation and not primary infection. Most people get the infection during childhood."

The researchers believe that treating HSV could affect AD. Lövheim stated “Concerning the future: we are approaching taking this into clinical studies, ie, to test whether antiviral drug treatment might slow the Alzheimer’s disease progression. I hope we will be able to start treatment studies within the next few years. If such treatment is proven to be efficient, it would be the final proof of the HSV-AD hypothesis and a great breakthrough for dementia research.”

Lövheim cautioned against current over-interpretations of the present work, however, and emphasized the need for more research, remarking “It is important to stress that at this point, no change in clinical guidelines can be recommended based on our results. Epidemiological results must first be verified in randomized treatment studies.”

Key points

• Herpes infection is associated with an increase in the risk for Alzheimer disease
• Herpes-associated antibodies significantly corresponded with AD risk in 2 studies
• Anti-viral treatments could slow the progression of Alzheimer disease, but more research is needed

References:

• Lövheim H, Gilthorpe J, Adolfsson R, et al. Reactivated herpes simplex infection increases the risk of Alzheimer’s disease. Alzheimers Dement. 2014. DOI: http://dx.doi.org/10.1016/j.jalz.2014.04.522
• Lövheim H, Gilthorpe J, Adolfsson R, et al. Herpes simplex infection and the risk of Alzheimer’s disease-A nested case-control study. Alzheimers Dement. 2014. DOI: http://dx.doi.org/10.1016/j.jalz.2014.07.157