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Herpes simplex virus (HSV) can remain dormant in the nervous system for years, occasionally reactivating to cause genital herpes or cold sores. Now a new study has linked reactivated HSV with Alzheimer’s disease (AD).

Researchers measured two antibodies against HSV in 3,432 people aged, on average, 62.7 years. During an average follow-up of 11.3 years, 7.6 per cent of those expressing anti-HSV IgG (a marker of historical infection) at baseline developed AD compared to 3.4 per cent of controls. This difference was not significant after controlling for age and sex. However 15.0 and 6.9 per cent of people who were positive and negative for anti-HSV IgM (a marker of reactivated infection) at baseline respectively developed AD. After controlling for possible confounders, expressing anti-HSV IgM at baseline doubled AD risk (hazard ratio 1.96).

The study joins a growing body of evidence, including another recent paper from the same group, linking HSV to at least some cases of AD. The antibodies do not differentiate HSV1 from HSV2 (responsible for cold sores and genital herpes respectively) but HSV1 is commoner and probably accounts for the link with AD, say the authors.

“Something which makes this hypothesis very interesting is that herpes infection can in principle be treated with antiviral agents,” says study author Hugo Lövheim, associate professor at the department of community medicine and rehabilitation, geriatric medicine, Umeå University. “Therefore, within a few years, we hope to be able to start studies in which we will also try treating patients to prevent the development of Alzheimer’s disease.”