It’s unusual for a scientific proposition to garner so much support that researchers and clinicians from around the world come together to express it. But that’s exactly what happened recently in the Journal of Alzheimer’s Disease, where 31 specialists from locations as varied as Spain, Finland and the United States co-authored an editorial proposing microbes – specifically, herpes simplex virus 1 (HSV1), Chlamydophila pneumoniae and spirochetes – as the major cause of Alzheimer’s disease (1).

“We write to express our concern that one particular aspect of the disease has been neglected,” the authors said, referencing studies implicating HSV1 and bacterial agents in disease-related changes to the brain. The editorial includes evidence for an infectious component of Alzheimer’s disease, including the presence of microbes in the brain, colocalization of pathogen signatures with disease pathology, and the fact that APOE polymorphisms affect susceptibility to both Alzheimer’s and infectious diseases. The editorial also discusses evidence for causation (such as amyloid beta deposition observed after infecting cell cultures and mouse models with HSV1) and mechanism (such as polymorphisms in the human cholesterol 25-hydroxylase gene CH25H, which is selectively upregulated by infection and governs both amyloid beta deposition and Alzheimer’s disease susceptibility).