The Herpes Simplex virus is a major precursor of Alzheimer's disease

Original Paper
Herpes simplex virus type 1 DNA is located within Alzheimer's disease amyloid plaques
MA Wozniak 1, AP Mee 2 a, RF Itzhaki 1 *
1Faculty of Life Sciences, University of Manchester, UK
2Department of Medicine, Manchester Royal Infirmary, UK

email: RF Itzhaki (ruth.itzhaki@manchester. ac.uk)

*Correspondence to RF Itzhaki, Faculty of Life Sciences (North Campus), Moffat Building, University of Manchester, PO Box 88, Manchester M60 1QD, UK.

aCurrent address: Directorate of Laboratory Medicine, CMMC, Oxford Road, Manchester M13 9PL, UK

No conflicts of interest were declared.

Keywords
brain • Alzheimer's disease • herpes simplex encephalitis • herpes simplex virus type 1 • amyloid plaques • apolipoprotein E • in situ polymerase chain reaction • thioflavin S staining • immunohistochemistry


Abstract
The brains of Alzheimer's disease sufferers are characterized by amyloid plaques and neurofibrillary tangles. However, the cause(s) of these features and those of the disease are unknown, in sporadic cases. We previously showed that herpes simplex virus type 1 is a strong risk factor for Alzheimer's disease when in the brains of possessors of the type 4 allele of the apolipoprotein E gene (APOE-4), and that -amyloid, the main component of plaques, accumulates in herpes simplex virus type 1-infected cell cultures and mouse brain. The present study aimed to elucidate the relationship of the virus to plaques by determining their proximity in human brain sections. We used in situ polymerase chain reaction to detect herpes simplex virus type 1 DNA, and immunohistochemistry or thioflavin S staining to detect amyloid plaques. We discovered a striking localization of herpes simplex virus type 1 DNA within plaques: in Alzheimer's disease brains, 90% of the plaques contained the viral DNA and 72% of the DNA was associated with plaques; in aged normal brains, which contain amyloid plaques at a lower frequency, 80% of plaques contained herpes simplex virus type 1 DNA but only 24% of the viral DNA was plaque-associated (p < 0.001). We suggest that this is because in aged normal individuals, there is a lesser production and/or greater removal of -amyloid (A), so that less of the viral DNA is seen to be associated with A in the brain. Our present data, together with our finding of A accumulation in herpes simplex virus type 1-infected cells and mouse brain, suggest that this virus is a major cause of amyloid plaques and hence probably a significant aetiological factor in Alzheimer's disease. They point to the usage of antiviral agents to treat the disease and possibly of vaccination to prevent it. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.