Microbes and Alzheimer’s Disease

We are researchers and clinicians working on Alzheimer’s disease (AD) or related topics, and we write to express our concern that one particular aspect of the disease has been neglected, even though treatment based on it might slow or arrest AD progression. We refer to the many studies, mainly on humans, implicating specific microbes in the elderly brain, notably herpes simplex virus type 1 (HSV1), Chlamydia pneumoniae, and several types of spirochaete, in the etiology of AD. Fungal infection of AD brain has also been described, as well as abnormal microbiota in AD patient blood. The first observations of HSV1 in AD brain were reported almost three decades ago. The ever-increasing number of these studies (now about 100 on HSV1 alone) warrants re-evaluation of the infection and AD concept.