Is Alzheimer's disease an infectious neurological disease? A review of the literature

INTRODUCTION: Alzheimer's disease (AD) is a leading cause of dementia around the globe. Its pathogenesis is characterized primarily by the extracellular deposition of amyloid β peptides and intracellular neurofibrillary tangles. Despite the significant investments in neurological research, the exact molecular mechanism of AD pathogenesis is still not fully elucidated. Several studies converge on a hypothesis that pathogenic microbes might play a role in AD progression. Although this hypothesis has been considered relatively weak for decades, it has recently received considerable attention due to increasing evidence on the association between microorganisms and AD. There is a lack of experimental and scientific arguments conveying that these microorganisms engender cognitive and neuropathological deficits and modifications specific to AD, challenging the theory that it could be an infectious neurological disease. This review focuses on recent advances in the infection hypothesis and provides an overview of new findings portraying the significance of pathogenic microbes in AD and the challenges confronting the validity of the hypothesis. METHODOLOGY: Data were collected from medical journals published on PubMed, Ovid MEDLINE, ScienceDirect, and Embase bibliographical databases with a predefined search strategy. All articles considering neurological disorders, especially AD associated with infectious diseases, were included. RESULTS: This work focused on providing an overview of new findings around the relationship between microorganisms and AD, challenges facing the validity of the theory, and recommendations on how the scientific community can best develop alternative approaches to address the pathophysiology of AD. CONCLUSION: While many studies reinforce the suspicion of an infectious etiology of AD, it is important to note that it is yet not validated how microorganisms’ presence in the brain can develop AD due to the limited available evidence. Certainly, ground‐breaking work is mandatory in this field of research, and these reports so far warrant a thorough investigation into how a chronic infection may remain silent while progressing its neuroinflammation. Amid this uncertainty arises the hope that many researchers will take on this challenge and join this endeavor to benefit AD patients worldwide.