Recent Insights into the Role of Herpesviridae in Alzheimer’s Disease: A Structured Narrative Review Based on a Systematic Literature Search

Background/Objectives: Herpesviridae have been increasingly investigated as possible contributors to Alzheimer’s disease (AD) because of their neurotropism, lifelong latency, and capacity to modulate inflammatory and amyloid-related pathways Methods: This structured narrative review, based on a systematic literature search, examined original studies published between December 2020 and December 2025 on the association between human herpesviridae and AD. Searches were conducted in PubMed, Web of Science, and Scopus using a PRISMA-informed screening framework. Results: The available evidence was heterogeneous across viruses and study designs. HSV-1 emerged as the most consistently implicated virus, supported by epidemiological, biomarker, neuroimaging, and experimental studies, although contradictory findings were also reported. VZV was mainly associated with AD through vascular, inflammatory, and vaccination-related evidence, with several studies suggesting lower dementia risk after zoster vaccination. CMV, EBV, and HHV-6 showed biologically plausible but less consistent associations, whereas HHV-7 and HHV-8 were supported only by limited or indirect evidence. Across studies, the proposed mechanisms included chronic neuroinflammation, vascular injury, amyloid and tau dysregulation, host immune responses, and cumulative infectious burden. Conclusions: Overall, the literature suggests that the relationship between herpesviridae and AD is not uniform and that HSV-1 appears to be the most relevant candidate. However, methodological heterogeneity, possible reverse causation, and unequal study intensity across viruses limit firm conclusions. More robust longitudinal and subtype-specific studies are needed to clarify causal relevance.