Polymicrobial Infections and Neurodegenerative Diseases

Purpose of Review Neurodegenerative diseases are a heterogeneous group of chronic disorders linked by the progressive degeneration of neurons in discrete regions of the central nervous system. Knowledge about the etiology of neurodegenerative diseases remains a major goal in modern medicinal research. In this review, we analyze and summarize the evidence for fungal and bacterial infections in the nervous tissue of patients with chronic neurodegenerative diseases. Recent Findings There is a growing body of evidence supporting the concept that polymicrobial infection could be the etiological agent for several neurodegenerative diseases. A variety of fungi and bacteria can be directly visualized in brain tissue from patients by immunohistochemistry using specific antibodies, and next-generation sequencing has recently revealed the identification of potentially causative microorganisms. Notably, the brain microbiota can vary from patient to patient, but importantly, some microbial genera are more relevant in a given disease. Multiple experimental approaches have identified a diversity of fungal and prokaryotic populations in the central nervous system of patients with different neurodegenerative disorders. This diversity present in each patient could account for the differences in the severity and evolution of clinical symptoms.