Do infectious agents play a role in dementia?

The number of people surviving to old age and concomitantly, the number affected by the diseases of old age, is increasing steadily. Alzheimer's disease (AD) affects one in five people aged over 80. The causes are unknown, but obviously, elucidation of the mechanisms of initiation and development of the disease is urgently required. This review describes studies on the possible role of infectious agents in dementia, particularly those on herpes simplex virus type 1, which, we discovered, resides latently in a high proportion of brains of the elderly and in combination with a certain genetic factor, is responsible for a high proportion of AD cases.