Does Dementia Have a Microbial Cause?

Area of Science:

• Neuroscience
• Infectious Diseases
• Pathology

Background:

• Alzheimer's disease (AD) is a progressive neurocognitive disorder characterized by neuronal loss, synaptic dysfunction, amyloid-beta (Aβ) plaques, and neurofibrillary tangles.
• The etiology of AD is complex and multifactorial, with ongoing research exploring various contributing factors.
• The role of pathogenic microbes in neurodegenerative diseases like AD is an area of significant scientific interest.

Purpose of the Study:

• To explore the potential contribution of pathogenic microbes to the development of dementia, specifically Alzheimer's disease.
• To review evidence supporting the AD pathogen hypothesis, which posits that microbes can trigger AD pathogenesis.
• To identify specific pathogens implicated in central nervous system (CNS) infections associated with AD.

Main Methods:

• Review of observational, epidemiological, experimental, and pathological studies.
• Examination of the AD pathogen hypothesis and its proposed mechanisms.
• Identification of microbial agents found in the AD brain.

Main Results:

• Evidence suggests a polymicrobial causality for dementia-inducing diseases.
• Specific pathogens including *Borrelia* sp., HSV-1, VZV (HHV-2), HHV-6/7, oral pathogens, *Chlamydophila pneumoniae*, and *Candida albicans* have been detected in the CNS of AD patients.
• These microbes can infect the CNS, evade immune responses, and persist in the AD brain.

Conclusions:

• Pathogenic microbes may act as triggers in AD, interacting with genetic factors to initiate Aβ accumulation, hyperphosphorylated tau (p-tau), and neuroinflammation.
• While significant progress has been made, the precise cause of Alzheimer's disease remains unclear.
• Further research is warranted to elucidate the role of microbial infections in AD pathogenesis.