Reactivated herpes simplex infection increases the risk of Alzheimer's disease

Abstract Background Previous studies have suggested a link between herpes simplex virus (HSV) type 1 and the development of Alzheimer's disease (AD). Methods The present analysis included 3432 persons (53.9% women, mean age at inclusion 62.7 ± 14.4 years) with a mean follow‐up time of 11.3 years. The number of incident AD cases was 245. Serum samples were analyzed for anti‐HSV antibodies (immunoglobulin (Ig)G and IgM) by enzyme‐linked immunosorbent assays. Results The presence of anti‐HSV IgG antibodies was not associated with an increased risk for AD, controlled for age and sex (hazard ratio, HR, 0.993, P = .979). However, the presence of anti‐HSV IgM at baseline was associated with an increased risk of developing AD (HR 1.959, P = .012). Conclusion Positivity for anti‐HSV IgM, a sign of reactivated infection, was found to almost double the risk for AD, whereas the presence of anti‐HSV IgG antibodies did not affect the risk.