Increased incidence of dementia following herpesvirus infection in the Korean population

Association between herpes simplex virus 1 and dementia: a systematic review protocol

INTRODUCTION

Herpes simplex virus 1 (HSV-1) infects approximately two-thirds of the global population under the age of 50 years. Although widely prevalent, the possible implications of HSV-1 in neurodegenerative diseases, especially dementia and Alzheimer's disease, remain poorly understood. This review seeks to elucidate this association and explore the potential benefits of preventing or treating herpesvirus infections on dementia risk. The goal is to enhance our understanding of HSV-1's potential role in dementia, which could inform the development of future therapeutic interventions for these conditions.

METHODS AND ANALYSIS

PubMed, Embase (Elsevier/Ovid), Web of Science, Scopus, Global Health, PsycInfo, Cochrane Library and Clinicaltrials.gov will be searched from the inception of each respective database. Studies that have HSV-1 as an exposure and dementia, or its subtypes, as a primary outcome will be included. Two researchers will independently screen titles, abstracts and full texts, with discrepancies resolved by a third researcher. Systematic data extraction from eligible studies will be performed using a standardised template. Risk of bias of individual studies will be assessed with the Cochrane Collaboration approach. We will assess the overall quality of cumulative evidence using the Grading of Recommendations, Assessment, Development and Evaluations criteria. Statistical analysis will employ a random effects model, and heterogeneity will be determined with Cochrane's Q test and assessed using I2. Studies will be grouped by population subgroups and dementia subtypes when possible to explore nuances in results. We will consider performing meta-regression if heterogeneity remains after subgroup analyses. All statistical analyses will be conducted using Stata V.18 software (College Station, Texas, USA).

ETHICS AND DISSEMINATION

No ethical approval is required since data will be collected from existing studies. The review will be disseminated through peer-reviewed publication and at national and international conferences.

PROSPERO REGISTRATION NUMBER

CRD42024516789.

[Varicella zoster infection as a risk factor for dementia: a scoping review]

A scoping review analyzing 21 selected publications was conducted to determine "whether the varicella zoster virus (VZV) is a risk factor for dementia". One meta-analysis concluded that VZV infection increases dementia risk, while another meta-analysis contradicts this finding. Several reports have shown an increased risk of dementia associated with VZV infections of the eyes and central nervous system. Additionally, a third meta-analysis reported that VZV vaccination reduces dementia. Therefore, VZV infection may be a risk factor for dementia. However, most of the reviewed articles were retrospective cohort studies, which limits the strength of conclusions that can be drawn. To provide more robust evidence, prospective cohort studies and clinical trials are needed to evaluate the impact of VZV itself, as well as the effectiveness of vaccines and antiviral therapies.

Increased risk of dementia associated with herpes simplex virus infections: Evidence from a retrospective cohort study using U.S. electronic health records

BACKGROUND

Alzheimer's disease is the most common age-related dementia. Recent compelling evidence from previous retrospective electronic health record (EHRs) studies suggests that herpes simplex virus (HSV) infections may be a risk factor for developing dementia. However, no age and propensity score matched studies have been published in a United States general population cohort study to date.

OBJECTIVE

We aimed to identify whether HSV infection shows a significantly increased risk of the development of dementia in a sizable and heterogeneous cohort. We investigated whether herpes simplex virus type 1 (HSV1), herpes simplex virus type 2 (HSV2), or coinfections with both serotypes pose a greater risk of developing dementia across different biological sexes and racial groups.

METHODS

EHRs from patients with a history of HSV or specific serotypes (HSV1 or HSV2) infection were selected for analysis. These records were compared to a propensity-matched control group and analyzed for hazard and odds ratios through TriNetX.

RESULTS

There was a significant difference in dementia incidence in the HSV-infected group versus the control. Individuals with a history of HSV, HSV1, HSV2, and coinfection all showed a significant risk of developing dementia compared to controls. Males with HSV2 are at a higher risk of dementia outcome than females with HSV2.

CONCLUSIONS

While consistent with previous reports, these findings are the first to establish a higher risk of developing dementia in patients who have any HSV diagnosis using a nationwide, population-based matched cohort study in the United States.

Association between herpes zoster and Parkinson's disease and dementia: a systematic review and meta-analysis

Objectives

This meta-analysis investigated the relationship between herpes zoster and the risk of dementia or Parkinson's disease by analyzing published clinical studies.

Methods

We systematically searched PubMed, Cochrane, Embase, and Web of Science Core Collection databases on April 25, 2024. Hazard ratios (HR) were used for statistical analyses. Random-effects models were applied, and heterogeneity was assessed using the I2 statistic.

Results

Herpes zoster was associated with a non-significant trend toward increased dementia risk (HR = 1.11, 95% CI 0.99-1.24, p = 0.07) but significantly increased Parkinson's disease risk (HR = 1.15, 95% CI 1.03-1.30, p = 0.02). Subgroup analyses revealed that herpes zoster significantly elevated the risk of the prospective study subgroup (HR = 1.08, 95% CI 1.02-1.13, p = 0.004) and vascular dementia subgroup (HR = 1.17, 95% CI 1.00-1.37, p = 0.05). Significant heterogeneity was observed for both outcomes (dementia: I 2 = 98%, p < 0.00001; Parkinson's disease: I 2 = 94%, p < 0.00001).

Conclusion

Herpes zoster raises the risk of Parkinson's disease and vascular dementia, with a potential causal link to dementia. Early vaccination against herpes zoster is recommended over post-infection antiviral treatment to mitigate risks.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/ and our registration number is CRD42024555620.

Herpes zoster and long-term risk of subjective cognitive decline

BACKGROUND

Herpes zoster (HZ), commonly known as "shingles," may contribute to cognitive decline through mechanisms such as neuroinflammation or direct neuronal injury. However, evidence on the longitudinal association between HZ and cognitive decline is conflicting and whether the risk differs by APOE ε4-carrier status has not been studied; prospective cohort studies on the association between HZ vaccination and cognitive decline are also lacking.

METHODS

We included 149,327 participants from three large cohorts-the Nurses' Health Study (NHS), NHSII, and Health Professionals Follow-Up Study (HPFS)-to prospectively examine the association between HZ and subsequent subjective cognitive decline (SCD). Poisson regression was used to estimate the multivariable-adjusted relative risk (MVRR) of a 3-unit increment in SCD score according to years since HZ compared with participants with no history of HZ.

RESULTS

Compared with individuals with no history of HZ, the MVRR (95% CI) of a 3-unit increment in SCD score was significantly and independently higher among individuals with a history of HZ, but the duration of time since HZ when the elevated risk of SCD was statistically significant differed among the cohorts. In NHS, HZ was associated with higher long-term risk of SCD; compared with individuals with no history of HZ, the MVRR (95% CI) of a 3-unit increment in SCD score was 1.14 (1.01, 1.32) for ≥ 13 years since HZ. In NHS II, HZ was associated with higher risk of SCD in both the short-term [MVRR 1.34 (1.18, 1.53) for 1-4 years] and long-term [MVRR 1.20 (1.08, 1.34) for ≥ 13 years since HZ]. In HPFS, an elevated risk of SCD was suggested across all time points. Among the subset of participants with information on APOE ε4, there was a suggestion that the association differed by APOE ε4 carrier status, but the results were not consistent between women and men. Among the subset of women with information on HZ vaccination, there was a suggestion that the long-term risk of SCD may be greater among women who were not vaccinated against HZ.

CONCLUSIONS

Data from three large independent cohorts of women and men showed that HZ was associated with higher long-term risk of SCD, and the risk may differ by APOE ε4-carrier status.

Contribution of CNS and extra-CNS infections to neurodegeneration: a narrative review

Central nervous system infections have been suggested as a possible cause for neurodegenerative diseases, particularly sporadic cases. They trigger neuroinflammation which is considered integrally involved in neurodegenerative processes. In this review, we will look at data linking a variety of viral, bacterial, fungal, and protozoan infections to Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis and unspecified dementia. This narrative review aims to bring together a broad range of data currently supporting the involvement of central nervous system infections in the development of neurodegenerative diseases. The idea that no single pathogen or pathogen group is responsible for neurodegenerative diseases will be discussed. Instead, we suggest that a wide range of susceptibility factors may make individuals differentially vulnerable to different infectious pathogens and subsequent pathologies.

Update on modifiable risk factors for Alzheimer's disease and related dementias

PURPOSE OF REVIEW

All human beings undergo a lifelong cumulative exposure to potentially preventable adverse factors such as toxins, infections, traumatisms, and cardiovascular risk factors, collectively termed exposome. The interplay between the individual's genetics and exposome is thought to have a large impact in health outcomes such as cancer and cardiovascular disease. Likewise, a growing body of evidence is supporting the idea that preventable factors explain a sizable proportion of Alzheimer's disease and related dementia (ADRD) cases.

RECENT FINDINGS

Here, we will review the most recent epidemiological, experimental preclinical, and interventional clinical studies examining some of these potentially modifiable risk factors for ADRD. We will focus on new evidence regarding cardiovascular risk factors, air pollution, viral and other infectious agents, traumatic brain injury, and hearing loss.

SUMMARY

While greater and higher quality epidemiological and experimental evidence is needed to unequivocally confirm their causal link with ADRD and/or unravel the underlying mechanisms, these modifiable risk factors may represent a window of opportunity to reduce ADRD incidence and prevalence at the population level via health screenings, and education and health policies.

The associations of herpes simplex virus and varicella zoster virus infection with dementia: a nationwide retrospective cohort study

BACKGROUND

In this study, the risk of dementia in patients with a history of herpes simplex virus (HSV) or varicella zoster virus (VZV) infection was evaluated.

METHODS

This nationwide cohort study used data from the Korean National Health Insurance Service collected between 2006 and 2017. A total of 752,205 subjects ≥ 45 years of age not diagnosed with dementia until 2006 were included. A multivariate Cox regression model, adjusted for age, sex, and other comorbidities, was used to assess the hazard ratio (HR) for dementia based on VZV or HSV infection. The interaction effects of both viral infections were analysed. Viral infections are classified into four categories: eye, central nervous system (CNS), simple, and complicated. The hazard ratio (HR) of viral infection was analysed based on the type of dementia.

RESULTS

In multivariable analysis, both HSV and VZV infection were associated with an increased risk of dementia (HR = 1.38, 95% confidence interval, CI:1.33-1.43) and (HR = 1.41, 95% CI:1.37-1.46), respectively. Patients who experienced both HSV and VZV infections were also at an increased risk of dementia (HR = 1.57, 95% CI:1.50-1.63). The co-infection group showed the shortest time from viral infection to dementia diagnosis (4.09 ± 3.02 years). In the subgroup analysis, all types of HSV and VZV infections were associated with an increased risk of dementia compared to the non-infection group. The eye, CNS, and complicated VZV infections were associated with a significantly higher risk than simple VZV infections. There were no significant differences between the subtypes of HSV infection. Furthermore, HSV, VSV, and co-infection were associated with an increased risk of all dementia types, including Alzheimer's disease (AD) and vascular dementia (VD).

CONCLUSIONS

Individual HSV and VZV infections were associated with an increased risk of all types of dementia, including AD and VD. Patients co-infected with HSV and VZV, VZV infection in the eye, CNS, or complicated type were more vulnerable to the development of dementia.

Risk of dementia following herpes zoster infection among patients undertreatment versus those not: A systematic review and meta-analysis

Background and Aims

According to the previous studies, herpes zoster (HZ) has been associated with cognitive function and dementia. There is a hypothesis claiming that dementia risk may be reduced by receiving the antiviral treatment for HZ. The purpose of this systematic review and meta-analysis was to shed light on the association between dementia and HZ in individuals receiving and not receiving antiviral medications.

Methods

Studies investigating the association between HZ and dementia were identified through a systematic search in PubMed/MEDLINE, Scopus, Embase, Google Scholar, and Cochrane Library databases from January, 2000 to April, 2022. Data on the risk of dementia in HZ-infected patients under and not under antiviral treatment were extracted. The meta-analysis was conducted using a random-effects model. The modified ROBIN-I tool was used to evaluate the risk of bias assessment. By utilizing the funnel plots, publication bias was investigated.

Results

Six cohort studies on 538,531 patients were included. The overall risk of bias assessment was moderate. According to evidence-based cohort studies, there was a significant direct association between HZ and risk of dementia in patients with HZ, who did not receive antiviral treatments (hazard ratio [HR]: 1.15, 95% confidence interval [CI]: 1.03 to 1.28, p = 0.01). On the other hand, there was an inverse relationship between HZ and risk of dementia among patients with HZ, who received antiviral treatments (HR: 0.68, 95% CI: 0.59 to 0.77, p < 0.001).

Conclusions

This study demonstrated that antiviral therapies may significantly lower the risk of dementia in patients with HZ. This study also confirmed that patients with HZ, without receiving antiviral therapies, may have an increased risk of developing dementia. Further longitudinal research is warranted in this area.

The association between varicella zoster virus and dementia: a systematic review and meta-analysis of observational studies

PURPOSE

The relationship between varicella zoster virus (VZV) infection and the risk of dementia has not been previously studied specifically. Therefore, this study sought to determine the relationship between studying VZV infection and dementia occurring in the general population by conducting an extensive meta-analysis of published cases.

METHOD

A systematic literature search was conducted in seven online databases by October 31, 2022. Heterogeneity was tested by the I2 index. Pooled HR and 95% CI were used to estimate the effect of VZV infection on dementia. Sensitivity analyses and publication bias were also performed.

RESULT

Nine studies involving 3,326,673 subjects were included. VZV infection was associated with an increased risk of dementia (HR = 1.11, 95% CI: 1.02-1.21). The risk of dementia was reduced in those who received antiviral therapy compared to those who did not (HR = 0.84, 95% CI: 0.71-0.99). In addition, VZV infection was found to be associated with an increased risk of developing dementia in the pooled results of the moderate quality study (HR = 1.81,95% CI: 1.27-2.59), and this association persisted when subgroup analyses were performed based on region (Asia: HR = 1.18,95% CI: 1.04-1.33).

CONCLUSIONS

Our results suggest that VZV infection might increase the risk of developing dementia, but there is no clear mechanism about the true relationship, and since there is no effective treatment for dementia, and our results suggest that some populations can benefit from antiviral therapy, it is at least arguable that patients who develop VZV infection should be treated with appropriate antiviral medications.

Cross-Sectional and Longitudinal Associations Between Treatment for Herpes Virus Infection and the Dispensing of Antidementia Medicines: An Analysis of the Australian Pharmaceutical Benefits Scheme Database

Background

Evidence from previous observational studies suggest that infection by herpes simplex virus (HSV) and varicella zoster virus (VZV) increase the risk of dementia.

Objective

To investigate if older adults exposed to HSV treatment have lower risk of dementia than the rest of the population.

Methods

We used the 10% Australian Pharmaceutical Benefits Scheme (PBS) database from 2013 to 2022 to ascertain the cross-sectional, time-series and longitudinal association between exposure to HSV treatment and the dispensing of antidementia medicines. Participants were men and women aged 60 years or older. We used Anatomical Therapeutic Chemical (ATC) codes to identify medicines dispensed for the treatment of HSV and dementia.

Results

During the year 2022 6,868 (1.2%) of 559,561 of participants aged 60 years or over were dispensed antidementia agent. The odds ratio (OR) of being dispensed an antidementia agent among individuals dispensed treatment for HSV was 0.73 (99% CI = 0.56-0.95). Multilevel logistic regression for the 2013-2022 period for those dispensed HSV treatment was 0.87 (99% CI = 0.75-1.00). Split-time span series from 2013 was associated with hazard ratio of 0.98 (99% CI = 0.89-1.07) for individuals dispensed relative to those not dispensed HSV treatment. All analyses were adjusted for age, sex, and the dispensing of medicines for the treatment of diabetes, hyperlipidemia, hypertension, and ischemic heart disease.

Conclusions

The dispensing of antiviral medicines for the treatment of HSV and VZV is consistently, but not conclusively, associated with decreased dispensing of antidementia medicines. This suggests that treatment of HSV and VZV infections may contribute to reduce the risk of dementia.

Melanin: a unifying theory of disease as exemplified by Parkinson's, Alzheimer's, and Lewy body dementia

Melanin, a ubiquitous dark pigment, plays important roles in the immune system, including scavenging reactive oxygen species formed in response to ultraviolet radiation absorption, absorbing metals, thermal regulation, drug uptake, innate immune system functions, redox, and energy transduction. Many tissue types, including brain, heart, arteries, ovaries, and others, contain melanin. Almost all cells contain precursors to melanin. A growing number of diseases in which there is a loss of melanin and/or neuromelanin are increasingly thought to have infectious etiologies, for example, Alzheimer's disease (AD), Parkinson's disease (PD), Lewy Body Dementia (LBD), and vitiligo. AD, PD, LBD, and vitiligo have been linked with herpesvirus, which enters melanosomes and causes apoptosis, and with gut dysbiosis and inflammation. Herpesvirus is also linked with gut dysbiosis and inflammation. We theorize that under normal healthy states, melanin retains some of the energy it absorbs from electromagnetic radiation, which is then used to fuel cells, and energy from ATP is used to compliment that energy supply. We further theorize that loss of melanin reduces the energy supply of cells, which in the case of AD, PD, and LBD results in an inability to sustain immune system defenses and remove the plaques associated with the disease, which appear to be part of the immune system's attempt to eradicate the pathogens seen in these neurodegenerative diseases. In addition, in an attempt to explain why removing these plaques does not result in improvements in cognition and mood and why cognitions and moods in these individuals have ebbs and flows, we postulate that it is not the plaques that cause the cognitive symptoms but, rather, inflammation in the brain resulting from the immune system's response to pathogens. Our theory that energy retained in melanin fuels cells in an inverse relationship with ATP is supported by studies showing alterations in ATP production in relationship to melanin levels in melanomas, vitiligo, and healthy cells. Therefore, alteration of melanin levels may be at the core of many diseases. We propose regulating melanin levels may offer new avenues for treatment development.

COVID-19 and Alzheimer's Disease: What Is the Connection?

Wang et al. found that elderly COVID-19 patients were at risk of AD. The following facts suggest a possible explanation: reactivation of herpes simplex virus type 1 (HSV1) and other herpesviruses can occur in SARS-CoV-2 patients; in cell cultures, HSV1 infection causes occurrence of many AD-like features, as does reactivation of latent HSV1 after addition of certain infectious agents; recurrent experimental reactivation of HSV1-infected mice leads to formation of the main features of AD brains, and to cognitive decline. These suggest that COVID-19 results in repeated reactivation of HSV1 in brain, with subsequent accumulation of damage and eventual development of AD.