Seasonal variation in multiple sclerosis relapse

Climate change impacts the symptomology and healthcare of multiple sclerosis patients through fatigue and heat sensitivity - A systematic review

BACKGROUND

Climate change, in terms of global warming and heat waves, might negatively impact people with neurological diseases. Patients with Multiple Sclerosis (MS), which is characterized by heat sensitivity, may therefore have an increased vulnerability. Subsequently, we aimed to specifically investigate the state of knowledge on climate change and MS.

METHODS

We conducted a literature search in the Pub Med database during 2022-2024 using the search terms "multiple sclerosis" AND "climate ", "climate change", "global warming", "heat waves", and "seasonal variations". A total of 773 scientifical papers were retrieved and scrutinized according to the inclusion/exclusion criteria. Finally, 24 publications were manually selected based on their relevance to the intended topic, covering climate change related heat sensitivity in MS patients, associated healthcare burden, and treatment strategies.

RESULTS

Only few publications focused on climate change and its effect on MS. The search yielded 24 articles on effects of climate/environmental heat and seasonal variations on MS. There was both evidence of worsened clinical symptoms as well as negative studies. However, the majority of selected papers, 16/24 (67 %) revealed an impact on MS symptoms/hospitalization from environmental heat.

CONCLUSIONS

So far there has been limited interest in the vulnerability of MS patients to climate change. The future perspective of increased temperature and heat waves should be highlighted so that authorities prepare health systems to apply to this new, but logical and intuitive, scientific knowledge. As heat sensitivity also seems to affect neurological disorders beyond MS, further research is needed to develop general care strategies in the future.

Observational study of gadolinium-enhancing lesions in MRI in patients with multiple sclerosis from the Spanish Mediterranean coast: Seasonal variability and relationship with climatic factors

INTRODUCTION

Environmental factors appear to play an important role in the development and course of Multiple Sclerosis (MS). Seasonal variability in disease activity has been described and it is postulated that it may vary according to geographical area. The aim of this study is to analyse the monthly distribution of activity observed on Magnetic Resonance Imaging (MRI) and to look for a possible relationship with climate in patients with relapsing remitting MS.

MATERIAL AND METHODS

Retrospective observational study, carried out in the population of one hospital on the Spanish Mediterranean coast. A total of 238 MRI scans of 51 patients were evaluated. Climatological data were obtained from the Spanish State Meteorological Agency from 2012 to 2016. Activity was defined as contrast-enhancing lesions.

RESULTS

The distribution of gadolinium-enhancing lesions was found to be non-uniform across months (p = 0.008). Visual inspection suggests higher activity in July and August. Regarding weather, tropical nights (defined as days with a minimum temperature above 20 °C) were associated with increased risk of MRI activity (OR = 1.06, p = 0.001).

CONCLUSION

These findings suggest a non-uniform monthly distribution of gadolinium-enhancing lesions and an association between warmer nights and increased MRI activity, pointing to a potential impact of environmental factors on multiple sclerosis activity in neuroimaging.

Study of seasonality of attacks in MOG antibody-associated disease

BACKGROUND

Seasonal variation in attacks of acute disseminated encephalomyelitis (ADEM1) is reported in some studies. Myelin oligodendrocyte glycoprotein (MOG) antibodies are found in up to 50 % of ADEM cases. Despite this, there has been no adequately powered study of seasonality in MOG antibody-associated disease (MOGAD). We sought to determine whether there was an effect of season on incidence of total attacks and onset attacks of MOGAD.

METHODS

We searched the large national Oxford-based NMO Service database to identify attacks of MOGAD occurring between 2010 and 2021. Month of each attack was extracted and Edwards' test of seasonal variation was applied to determine whether there was a seasonal effect on total attacks and onset attacks.

RESULTS

Neither incidence of total attacks nor incidence of onset attacks varied significantly by month.

CONCLUSION

There is no evidence of seasonal fluctuations in the incidence of MOGAD attacks in the UK.

Risk of Relapse After COVID-19 Vaccination Among Patients With Multiple Sclerosis in France: A Self-Controlled Case Series

BACKGROUND AND OBJECTIVES

People with multiple sclerosis (MS) have an increased risk of severe coronavirus infection due to their level of motor disability or exposure to certain immunosuppressive treatments. Thus, patients with MS have had priority access to coronavirus disease 2019 (COVID-19) vaccination. However, relapses after vaccination have been reported, leading some patients to not seek the recommended booster doses. The main objective was to estimate the risk of severe relapse after 1, 2, and 3 (booster) doses of COVID-19 vaccination in patients with MS. The secondary objectives were to assess the risk of relapse in clinically meaningful subgroups according to the type of vaccine, the characteristics of the patients, and the use of disease-modifying treatments (DMTs).

METHODS

We conducted a nationwide study using data from the French National Health Data System. Patients with MS were identified according to ICD codes, specific treatments, and reimbursement data up to March 31, 2022. Relapses requiring treatment with high-dose corticosteroids were identified. A self-controlled case series method was used to evaluate the risk of relapse associated with COVID-19 vaccines in the 45 days after vaccination. The associated risk was evaluated after 1, 2, or 3 (booster) doses and is expressed as overall incidence rate ratios (IRRs) and in subgroups of interest.

RESULTS

Overall, 124,545 patients with MS were identified on January 1, 2021, and 82% received at least 1 dose of a COVID-19 vaccine (n = 102,524) until December 31, 2021, for a total of 259,880 doses. The combined IRR for MS relapse was 0.97 (0.91-1.03, p = 0.30). The same absence of risk was confirmed in various subgroups (age younger than 50 years, duration of MS < 10 years, use of DMT). A small increase in the relapse risk cannot be excluded after a booster dose (IRR 1.39 [1.08-1.80]) for patients with high MS activity, especially when not treated.

DISCUSSION

There is no increased risk of relapse requiring corticosteroid therapy after COVID-19 vaccination for almost all patients. We cannot exclude an increased risk after the booster dose for patients who have had at least 2 relapses in the previous 2 years.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that COVID-19 vaccination does not increase the risk of severe relapse in patients with MS.

Epidemiology and natural history of POLG disease in Norway: a nationwide cohort study

OBJECTIVE

To investigate the prevalence and natural history of POLG disease in the Norwegian population.

METHODS

A national, population-based, retrospective study using demographic, clinical, and genetic data of patients with genetically confirmed POLG disease. The patients were diagnosed between 2002 and 2022, and were included into the Norwegian POLG Patient Registry. Patients were stratified according to age at disease onset (early <12 years, juvenile to adult 12-40 years, late ≥40 years) and resident region.

RESULTS

Ninety-one patients were included. The point prevalence of POLG disease was 1:149,253. Birth prevalence was 1:48,780. Median age at clinical onset was 16 years (range: 2 months to 70 years). Onset occurred early in 35% (32 out of 91), juvenile-adult in 55% (50 out of 91) and late in 10% (9 out of 91). A distinct seasonal pattern in disease onset was observed, with 57% (52 out of 91) presenting between May and August. Forty-five patients (49%) had acute exacerbations that required intensive care, and this affected 72% of those in the early-onset group. The mortality rate was 54% (49 out of 91), with a median time from disease onset to death of 3 years (range: 1 month to 36 years).

INTERPRETATION

We provide the point prevalence and birth prevalence of POLG disease in the first nationwide study in which epidemiological and clinical data were integrated. Seasonal variations in clinical onset may offer valuable insights into disease mechanisms and modifying factors. The findings from this study are crucial for quantifying the disease burden, and contribute to evidence-based healthcare planning.

Seasonality and clinical characteristics of MS in an equatorial country

BACKGROUND

Month and season of birth have been associated with risk of multiple sclerosis (MS), but there is relatively little evidence regarding their influence on the timing and severity of disease at onset.

OBJECTIVE

To assess whether month and season of birth influence the age and phenotype at onset of MS as well as its severity in a cohort of Colombian patients.

METHODS

This study is an analysis on MS cases only, drawn from a previously published case-control study. MS cases confirmed with current diagnostic criteria cared for at least once in our center were included. We assessed the influence of the month and season of birth in the age at MS onset, MS severity score, and age-related MS severity score using multiple and pairwise comparisons. Age at onset was also studied using Kaplan-Meier survival estimates compared with the log-rank test. The likelihood of progressive MS onset was evaluated with OR estimated from logistic regression models adjusted for age at onset and sex.

RESULTS

668 MS cases were included. No significant differences were found in the age at MS onset according to month of birth or season of birth. Neither month of birth nor season of birth conferred significant differences in MS severity score or age-related MS severity score. No significant association was found between month (ORs ranging from 0.62 to 3.11, none significant) or season of birth (OR 0.91; 95 %CI: 0.46-1.84) with primary progressive MS.

CONCLUSION

The month or season of birth do not appear to influence the age onset and phenotype of MS in our country.

Occurrence and Risk Factors of Relapse Activity after Vaccination against COVID-19 in People with Multiple Sclerosis: 1-Year Follow-Up Results from a Nationwide Longitudinal Observational Study

Several studies reported post-SARS-CoV-2-vaccination (PV) symptoms. Even people with multiple sclerosis (PwMS) have concerns about disease activity following the SARS-CoV-2 vaccination. We aimed to determine the proportion of PwMS with PV relapses, the PV annualized relapse rate (ARR), the time from vaccination to subsequent relapses, and identify sociodemographic/clinical risk factors for PV relapses. PwMS were surveyed several times at baseline and four follow-ups as part of a longitudinal observational study regarding the safety and tolerability of the SARS-CoV-2 vaccination. The inclusion criteria for this analysis were age ≥18 years, ≥1 SARS-CoV-2 vaccination, and ≥1-year observation period since initial vaccination. Of 2466 PwMS, 13.8% reported PV relapses (mostly after second [N = 147] or booster vaccination [N = 145]) at a median of 8.0 (first/third quantile: 3.55/18.1) weeks PV, with the shortest period following initial vaccination (3.95 weeks). The ARR was 0.153 (95% confidence interval: 0.138-0.168), with a median observation period since initial vaccination of 1.2 years. Risk factors for PV relapses were younger age, female gender, moderate-severe disability levels, concurrent autoimmune diseases, relapsing-remitting MS courses, no DMT, and relapses within the year prior to the first vaccination. Patients' health conditions before/during initial vaccination may play a more important role in PV relapse occurrence than vaccination per se.

Presentations to eye emergency departments with flashes and floaters differ dependent on incident solar radiation

AIM

The aim of this retrospective review was to analyse the frequency of patients presenting with flashes and/or floaters (F/F) on bright versus dark days to the eye emergency department of a tertiary referral hospital (the Mater Misericordiae University Hospital) over a 3-year period. The diagnostic and clinical outcomes of F/F presentations were also analysed.

METHODS

This retrospective study assessed eye casualty attendances between January 2018 and December 2020. Solar irradiation (j/cm2) at ground level was retrieved from the records of Met Eireann (Irish National Meteorological Service) via their open access records. A review of electronic patient medical records using the in-house database patient centre was carried out of all patients who attended EED of during the study timeline on the 5 'brightest' and 5 'darkest' days of each year.

RESULTS

Seven hundred forty patient presentations were analysed in total. Overall, 16% (n = 119) of all patients that attended EED during the timeframe of the study presented with F/F. One hundred six patients (89%) presented with floaters, 40 patients (34%) presented with flashing lights/photopsia, and 35 patients (29%) presented with both F/F. More patients presented to EED with F/F on bright days when compared with dark days (74 vs 45, p < 0.05). Eighty-nine percent of all patients with F/F presented with monocular floaters. There were more floater presentations during bright when compared with dark days (70 vs 36, p < 0.05). More patients were diagnosed with PVD on bright days when compared with those diagnosed with PVD on dark days (43vs 15, p < 0.05). More RDs were diagnosed on dark days compared with bright days (7 vs 3, p < 0.05).

CONCLUSION

This study established that F/F presentations were more likely to present during bright days when compared with dark days. The diagnosis of PVD was more common during bright days, and RDs were diagnosed significantly more frequently on dark days. Although incident solar radiation was correlated with greater floaters/PVD presentation, causation is unlikely, and the duration of PVD may have been longer in patients presenting on bright days (i.e. pseudo-sudden symptoms).

Frequency and Predictors of Relapses following SARS-CoV-2 Vaccination in Patients with Multiple Sclerosis: Interim Results from a Longitudinal Observational Study

Despite protection from severe COVID-19 courses through vaccinations, some people with multiple sclerosis (PwMS) are vaccination-hesitant due to fear of post-vaccination side effects/increased disease activity. The aim was to reveal the frequency and predictors of post-SARS-CoV-2-vaccination relapses in PwMS. This prospective, observational study was conducted as a longitudinal Germany-wide online survey (baseline survey and two follow-ups). Inclusion criteria were age ≥18 years, MS diagnosis, and ≥1 SARS-CoV-2 vaccination. Patient-reported data included socio-demographics, MS-related data, and post-vaccination phenomena. Annualized relapse rates (ARRs) of the study cohort and reference cohorts from the German MS Registry were compared pre- and post-vaccination. Post-vaccination relapses were reported by 9.3% PwMS (247/2661). The study cohort's post-vaccination ARR was 0.189 (95% CI: 0.167-0.213). The ARR of a matched unvaccinated reference group from 2020 was 0.147 (0.129-0.167). Another reference cohort of vaccinated PwMS showed no indication of increased post-vaccination relapse activity (0.116; 0.088-0.151) compared to pre-vaccination (0.109; 0.084-0.138). Predictors of post-vaccination relapses (study cohort) were missing immunotherapy (OR = 2.09; 1.55-2.79; p < 0.001) and shorter time from the last pre-vaccination relapse to the first vaccination (OR = 0.87; 0.83-0.91; p < 0.001). Data on disease activity of the study cohort in the temporal context are expected for the third follow-up.

Seasonal Changes in Serum Metabolites in Multiple Sclerosis Relapse

Multiple sclerosis (MS) is a debilitating chronic disease of unknown etiology. There are limited treatment options due to an incomplete understanding of disease pathology. The disease is shown to have seasonal exacerbation of clinical symptoms. The mechanisms of such seasonal worsening of symptoms remains unknown. In this study, we applied targeted metabolomics analysis of serum samples using LC-MC/MC to determine seasonal changes in metabolites throughout the four seasons. We also analyzed seasonal serum cytokine alterations in patients with relapsed MS. For the first time, we can demonstrate seasonal changes in various metabolites in MS compared to the control. More metabolites were affected in MS in the fall season followed by spring, while summer MS was characterized by the smallest number of affected metabolites. Ceramides were activated in all seasons, suggesting their central role in the disease pathogenesis. Substantial changes in glucose metabolite levels were found in MS, indicating a potential shift to glycolysis. An increased serum level of quinolinic acid was demonstrated in winter MS. Histidine pathways were affected, suggesting their role in relapse of MS in the spring and fall. We also found that spring and fall seasons had a higher number of overlapping metabolites affected in MS. This could be explained by patients having a relapse of symptoms during these two seasons.

Seasonal and monthly variation in multiple sclerosis relapses: a systematic review and meta-analysis

BACKGROUND

Multiple Sclerosis (MS) relapses are episodes of transient disease exacerbation. There are contradictory findings regarding seasonal variation in MS relapses. In this systematic review and meta-analysis, we aimed to investigate the seasonal and monthly variation in relapse rates among patients with MS.

METHODS

We systematically queried PubMed, Scopus, and Web of Science for published papers until February 30, 2022.

RESULTS

A total of 24 studies were included in this systematic review and meta-analysis with a total of 29,106 patients with MS. We found that the relapse rate was significantly lower in fall compared to the average relapse rate in other seasons with a risk ratio (RR) of 0.97 (95% CI 0.95-0.98). Furthermore, patients with MS experienced a higher number of relapses in April (RR: 1.06, 95% CI 1.01-1.11) and March (RR: 1.08, 95% CI 1.00-1.16) compared to other months. Also, the risk of relapse was lower in August (RR: 0.92, 95% CI.85-0.98), September (RR: 0.97, 95% CI.94-0.99), October (RR: 0.92, 95% CI.89-0.96), and November (RR: 0.93, 95% CI.89-0.97).

CONCLUSION

Our systematic review and meta-analysis confirm the temporal fluctuations in the relapse of MS through a comprehensive review of the existing literature, with a lower relapse rate during late summer and fall and a higher relapse rate during early spring.

Circadian rhythm and disease: Relationship, new insights, and future perspectives

The circadian system is responsible for internal functions and regulation of the organism according to environmental cues (zeitgebers). Circadian rhythm dysregulation or chronodisruption has been associated with several diseases, from mental to autoimmune diseases, and with life quality change. Following this, some therapies have been developed to correct circadian misalignments, such as light therapy and chronobiotics. In this manuscript, we describe the circadian-related diseases so far investigated, and studies reporting relevant data on this topic, evidencing this relationship, are included. Despite the actual limitations in published work, there is clear evidence of the correlation between circadian rhythm dysregulation and disease origin/development, and, in this way, clock-related therapies emerge as great progress in the clinical field. Future improvements in such interventions can lead to the development of successful chronotherapy strategies, deeply contributing to enhanced therapeutic outcomes.

Effect of Seasonal Variation on Relapse Rate in Patients With Relapsing-Remitting Multiple Sclerosis in Saudi Arabia

Multiple sclerosis (MS) is becoming a global subject of study in which some demographic variations are thought to be correlated with its activity. Relapsing-remitting multiple sclerosis (RRMS) is the most common demyelinating disorder, characterized by periods of exacerbating attacks, followed by partial or complete remission. Several factors might play a role in disease progression and relapse frequency, such as vitamin D, ultraviolet B radiation, estrogen levels, smoking, obesity, and unhealthy lifestyles. In this study, we identified the relationship between seasonal variation and relapse rate and correlated the latter with sex, age, and vitamin D levels in patients with RRMS in Jeddah, Saudi Arabia. We retrospectively collected data from 182 RRMS patients between 2016 and 2021. A total of 219 relapses were documented in 106 patients (58.2 %). The relapse per patient ratio showed a sinusoidal pattern, peaking in January at a rate of 0.49 and troughed in June at a rate of 0.18. There was no difference in relapse rates between men and women (p =0.280). There was a significant negative correlation between vitamin D levels and relapse rate (r = −0.312, p =0.024). Therefore, the relapse rate was higher during the winter and was correlated with low vitamin D levels. However, relapses are likely multifactorial, and more population-based studies are needed to understand the role of environmental variables in MS exacerbation. A better understanding of this relationship will allow for improved treatment and possibly better prevention of relapse.

Seasonal variation in attacks of neuromyelitis optica spectrum disorders and multiple sclerosis: Evaluation of 794 attacks from a nationwide registry in Argentina

BACKGROUND

Identification of triggers that potentially instigate attacks in neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) has remained challenging. We aimed to analyze the seasonality of NMOSD and MS attacks in an Argentinean cohort seeking differences between the two disorders.

METHODS

A retrospective study was conducted in a cohort of NMOSD and MS patients followed in specialized centers from Argentina and enrolled in RelevarEM, a nationwide, longitudinal, observational, non-mandatory registry of MS/NMOSD patients. Patients with complete relapse data (date, month and year) at onset and during follow-up were included. Attack counts were analyzed by month using a Poisson regression model with the median monthly attack count used as reference.

RESULTS

A total of 551 patients (431 MS and 120 NMOSD), experiencing 236 NMOSD-related attacks and 558 MS-related attacks were enrolled. The mean age at disease onset in NMOSD was 39.5 ± 5.8 vs. 31.2 ± 9.6 years in MS (p < 0.01). Mean follow-up time was 6.1 ± 3.0 vs. 7.4 ± 2.4 years (p < 0.01), respectively. Most of the included patients were female in both groups (79% vs. 60%, p < 0.01). We found a peak of number of attacks in June (NMOSD: 28 attacks (11.8%) vs MS: 33 attacks (5.9%), incidence rate ratio 1.82, 95%CI 1.15-2.12, p = 0.03), but no differences were found across the months in both disorders when evaluated separately. Strikingly, we observed a significant difference in the incidence rate ratio of attacks during the winter season when comparing NMOSD vs. MS (NMOSD: 75 attacks (31.7%) vs MS: 96 attacks (17.2%), incidence rate ratio 1.82, 95%CI 1.21-2.01, p = 0.02) after applying Poisson regression model. Similar results were observed when comparing the seropositive NMOSD (n = 75) subgroup vs. MS.

CONCLUSIONS

Lack of seasonal variation in MS and NMOSD attacks was observed when evaluated separately. Future epidemiological studies about the effect of different environmental factors on MS and NMOSD attacks should be evaluated prospectively in Latin America population.

Case Report: Multiple Sclerosis Relapses After Vaccination Against SARS-CoV2: A Series of Clinical Cases

Objective: To describe a temporal association between COVID-19 vaccine administration and multiple sclerosis (MS) relapses.

Methods: This case series study was collected in four MS Centres in Central Italy, using data from 16 MS patients who received COVID-19 vaccination and presented both clinically and radiologically confirmed relapses between March and June 2021. We collected patients' relevant medical history, including demographics, MS clinical course, disease-modifying treatment (DMT) received (if applicable), and data from MRI scans obtained after the COVID-19 vaccination.

Results: Three out of 16 patients received a diagnosis of MS with a first episode occurring after COVID-19 vaccination; 13 had already a diagnosis of MS and, among them, 9 were on treatment with DMTs. Ten patients received BNT162b2/Pfizer-BioNTech, 2 patients mRNA-1273/Moderna, and 4 patients ChAdOx1 nCoV-19/AstraZeneca. All MS relapses occurred from 3 days to 3 weeks after receiving the first dose of the COVID-19 vaccination or the booster. All patients had evidence of radiological activity on MRI.

Discussion: Clinical and radiological findings in these cohort of MS patients confirmed disease re/activation and suggested a temporal association between disease activity and COVID-19 vaccination. The nature of this temporal association, whether causative or incidental, remains to be established.

Evaluation of non-endemic pemphigus foliaceus in a large series of patients: a single-center retrospective study from Turkey focuses on the relapses

BACKGROUND

Pemphigus foliaceus is exceedingly rare around the world, except within the few regions where it occurs as an endemic variant. Various factors can trigger immune mechanisms that induce pemphigus foliaceus or worsen its course.

OBJECTIVE

To determine the demographic and clinical characteristics of the patients with pemphigus foliaceus in a large series from a non-endemic country, investigate the triggering factors, and seasonal patterns.

METHODS

The data of the patients diagnosed with pemphigus foliaceus in the study's center between 1989-2018 were retrospectively analyzed.

RESULTS

Sixty-eight patients (mean age, 45.7 ± 14.5 years) were included in the study. The number of onsets reached its peak in spring-summer (p = 0.008). A total of 117 relapses occurred in 42 patients and were most common in spring-summer (not significant). Specific trigger factors were detected in 45 relapses. In the other 72 relapses, the peak was observed in spring-summer (p = 0.005). There were no significant differences in the demographic and clinical variables investigated between relapsed and non-relapsed patients.

STUDY LIMITATIONS

Retrospective design.

CONCLUSIONS

Triggering factors could not be identified in more than half of the relapses in the study's series. The subgroup of relapses (without identified causes), as well as the onsets of the disease, showed a significant seasonal variation with a peak in spring-summer; however, the seasonal variable did not justify the total group of relapses. Although the seasonal variation may be caused by a combination of factors, UV radiation should be considered a trigger factor for the peaks in spring-summer, particularly in Turkey.

Seasonal and daytime variation in multiple immune parameters in humans: Evidence from 329,261 participants of the UK Biobank cohort

Seasonal disease outbreaks are perennial features of human infectious disease but the factors generating these patterns are unclear. Here we investigate seasonal and daytime variability in multiple immune parameters in 329,261 participants in UK Biobank and test for associations with a wide range of environmental and lifestyle factors, including changes in day length, outdoor temperature and vitamin D at the time the blood sample was collected. Seasonal patterns were evident in lymphocyte and neutrophil counts, and C-reactive protein CRP, but not monocytes, and these were independent of lifestyle, demographic, and environmental factors. All the immune parameters assessed demonstrated significant daytime variation that was independent of confounding factors. At a population level, human immune parameters vary across season and across time of day, independent of multiple confounding factors. Both season and time of day are fundamental dimensions of immune function that should be considered in all studies of immuno-prophylaxis and disease transmission.

Drivers of Infectious Disease Seasonality: Potential Implications for COVID-19

Not 1 year has passed since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19). Since its emergence, great uncertainty has surrounded the potential for COVID-19 to establish as a seasonally recurrent disease. Many infectious diseases, including endemic human coronaviruses, vary across the year. They show a wide range of seasonal waveforms, timing (phase), and amplitudes, which differ depending on the geographical region. Drivers of such patterns are predominantly studied from an epidemiological perspective with a focus on weather and behavior, but complementary insights emerge from physiological studies of seasonality in animals, including humans. Thus, we take a multidisciplinary approach to integrate knowledge from usually distinct fields. First, we review epidemiological evidence of environmental and behavioral drivers of infectious disease seasonality. Subsequently, we take a chronobiological perspective and discuss within-host changes that may affect susceptibility, morbidity, and mortality from infectious diseases. Based on photoperiodic, circannual, and comparative human data, we not only identify promising future avenues but also highlight the need for further studies in animal models. Our preliminary assessment is that host immune seasonality warrants evaluation alongside weather and human behavior as factors that may contribute to COVID-19 seasonality, and that the relative importance of these drivers requires further investigation. A major challenge to predicting seasonality of infectious diseases are rapid, human-induced changes in the hitherto predictable seasonality of our planet, whose influence we review in a final outlook section. We conclude that a proactive multidisciplinary approach is warranted to predict, mitigate, and prevent seasonal infectious diseases in our complex, changing human-earth system.

Seasonal patterns of relapse and disability in Danish MS patients: A population-based cohort study

BACKGROUND

The importance of environmental risk factors in the onset of multiple sclerosis (MS) has been studied extensively. Similarly, a growing number of studies address the importance of environmental factors, including seasonality, for ongoing activity of established disease. Specifically, past research demonstrates higher rates of relapse activity in summer months among individuals with MS. Our study adds to the existing literature on seasonality of disease relapse by analysing a large population-based and virtually complete cohort of patient with relapsing and remitting MS (RRMS) in an area of temperate climate.

METHODS

The Danish Multiple Sclerosis Registry includes follow-up for all patients receiving disease modifying treatment from 1996-2020, with near-complete registration of all relapses and their dates. We compared the observed and expected numbers of relapses for each calendar month and calculated month-specific annualized relapse rates (ARR) using Poisson regression. In addition, we analysed seasonal variation in disability as measured by the Expanded Disability Status Scale (EDSS).

RESULTS

From 1996 to 2020 we followed 13,575 MS patients treated with disease modifying therapy (4165 men and 9410 women) for a total of 82,187 person years and 134,593 control visits. The mean age at entry was 41.1 years with standard deviation 10.9 years. We recorded 16,083 relapses throughout the observation period, and for 15,728 of the relapses the date of onset was known. Relapses were unevenly distributed by calendar month (p < 0.00001). The most prominent deviation was a paucity of relapses in July in which the ARR was 0.166 compared with mean of 0.191 for the whole year. Otherwise, the ARR formed a plateau slightly above mean during the spring months. Mean EDSS was slightly higher in autumn (2.78) than in spring (2.74), but there was no difference between winter and summer; p < 0.0001.

CONCLUSION

In contrast with previous studies, we observed a nadir of relapses in July among Danish patients with RRMS. This finding may be related to increased exposure to sunlight in the summer, particularly during vacation when outdoor recreational activities are more frequent and potential exposure to infections is decreased. Confirmation of this in future studies is warranted.

Seasonal variation of onset in patients with anti-aquaporin-4 antibodies and anti-myelin oligodendrocyte glycoprotein antibody

This study aimed to determine the seasonal impact on the clinical onset of inflammatory neurological diseases of the central nervous system by analyzing the onset month with information on clinical manifestations in Japanese patients. As a result, patients with anti-aquaporin-4 antibodies (AQP4-IgG)-positive neuromyelitis optica spectrum disorders (NMOSD) showed spring-summer predominance of the clinical onset. Conversely, patients with anti-myelin oligodendrocyte glycoprotein antibody (MOG-IgG)-associated disease showed autumn-winter predominance of the clinical onset. Both seasonal variations were irrespective of the clinical manifestation. Environmental factors with seasonal variation influence the development of neurological conditions related to AQP4-IgG and MOG-IgG.

Seasonal Variations in Macrophages/Microglia Underlie Changes in the Mouse Model of Multiple Sclerosis Severity

Both immune and neurodegenerative mechanisms underlie multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). MS/EAE are triggered by encephalitogenic immune cells, including Th1 and Th17 cells, whereas T regulatory (Treg) cells are involved in inflammation resolution. Pro-inflammatory macrophages/microglia also play a deleterious role in the disease. Seasonal variations in MS relapses, active lesions, and pro- and anti-inflammatory cytokine levels have been described in MS patients and have been related with both perinatal and adult exposure to sunlight and other environmental factors. However, some data in EAE mice suggest that these variations might be, at least partially, endogenously determined. Thus, our objective was to study the effect of the season of birth and disease induction on the course of EAE, and immune cell infiltration in the central nervous system (CNS) in myelin oligodendrocyte glycoprotein (MOG_35-55)-induced EAE in 8 weeks old, female C57BL/6N mice maintained under constant, controlled conditions. EAE severity as well as pathogenic (Th1, Th17, macrophages/microglia) and protective (Treg) subsets was found to vary according to the season of birth or of EAE induction. Summer-born or summer-immunized animals developed a milder disease, which coincided with variations in numbers of T effector/regulatory subsets, and significantly low numbers of macrophages/microglia. These results suggest that endogenous rhythms in immune responses might cause seasonal variations in EAE severity, and, maybe, in the course of MS, and that they might be related to macrophages/microglia.

Relapse Patterns in NMOSD: Evidence for Earlier Occurrence of Optic Neuritis and Possible Seasonal Variation

Neuromyelitis optica spectrum disorders (NMOSD) and multiple sclerosis (MS) show overlap in their clinical features. We performed an analysis of relapses with the aim of determining differences between the two conditions. Cases of NMOSD and age- and sex-matched MS controls were collected from across Australia and New Zealand. Demographic and clinical information, including relapse histories, were recorded using a standard questionnaire. There were 75 cases of NMOSD and 101 MS controls. There were 328 relapses in the NMOSD cases and 375 in MS controls. Spinal cord and optic neuritis attacks were the most common relapses in both NMOSD and MS. Optic neuritis (p < 0.001) and area postrema relapses (P = 0.002) were more common in NMOSD and other brainstem attacks were more common in MS (p < 0.001). Prior to age 30 years, attacks of optic neuritis were more common in NMOSD than transverse myelitis. After 30 this pattern was reversed. Relapses in NMOSD were more likely to be treated with acute immunotherapies and were less likely to recover completely. Analysis by month of relapse in NMOSD showed a trend toward reduced risk of relapse in February to April compared to a peak in November to January (P = 0.065). Optic neuritis and transverse myelitis are the most common types of relapse in NMOSD and MS. Optic neuritis tends to occur more frequently in NMOSD prior to the age of 30, with transverse myelitis being more common thereafter. Relapses in NMOSD were more severe. A seasonal bias for relapses in spring-summer may exist in NMOSD.

Seasonal distribution of attacks in aquaporin-4 antibody disease and myelin-oligodendrocyte antibody disease

BACKGROUND

Seasonal variation in incidence and exacerbations has been reported for neuroinflammatory conditions such as multiple sclerosis and acute disseminated encephalomyelitis (ADEM). It is unknown whether seasonality also influences aquaporin-4 antibody (AQP4-Ab) disease and myelin-oligodendrocyte antibody (MOG-Ab) disease.

OBJECTIVE

We examined the seasonal distribution of attacks in AQP4-Ab disease and MOG-Ab disease.

METHODS

Observational study using data prospectively recorded from three cohorts in the United Kingdom.

RESULTS

There was no clear seasonal variation in AQP4-Ab or MOG-Ab attacks for either the onset attack nor subsequent relapses. In both groups, the proportion of attacks manifesting with each of the main phenotypes (optic neuritis, transverse myelitis, ADEM/ADEM-like) appeared stable across the year. This study is the first to examine seasonal distribution of MOG-Ab attacks and the largest in AQP4-Ab disease so far.

CONCLUSION

Lack of seasonal distribution in AQP4-Ab and MOG-Ab disease may argue against environment factors playing a role in the aetiopathogenesis of these conditions.

Differential Expression of HERV-W in Peripheral Blood in Multiple Sclerosis and Healthy Patients in Two Different Ethnic Groups

Overexpression of the Human endogenous retrovirus W (HERV-W) group of inherited retroviruses has been consistently linked with Multiple Sclerosis (MS). However most of the studies on this link have focused on European genetic groups with a very high risk of MS and it is not clear that this relationship holds for all ethnic groups. This study examined via qPCR the RNA expression in peripheral blood of HERV-W (the multiple sclerosis associated retrovirus variant MSRV) of MS patients and healthy controls from two ethnic groups with very different risk rates of MS. Population one was derived from the UK with a Northern European genetic background and an MS risk rate of 108/100,000, population two was derived from the republic of Tatarstan, Russian Federation, with a mixed Russian (Eastern European) and Tartar (Turkic or Volga/Urals) population with an MS risk rate of 21-31/100,000. The Russian population displayed a significantly higher basal level of expression of MSRV in both healthy and MS individuals when compared to the British control population with a trend in the Russian population towards higher expression levels in MS patients than healthy patients.

Circadian rhythms in adaptive immunity

The circadian clock provides organisms with the ability to track time of day, allowing them to predict and respond to cyclical changes in the external environment. In mammals this clock consists of multiple auto-regulatory feedback loops generated by a network of circadian clock proteins. This network provides the fundamental basis for rhythms in behaviour and physiology. This clockwork machinery exists in most cells, including those of the immune system. In recent years evidence has emerged highlighting the important role of molecular clocks in dictating the response of immune pathways. While initial work highlighted the effect of the clock in the 'first line of defence', the innate immune system, it has become increasingly apparent that it also plays a role in the more tailored, later-stage adaptive immune response. This review provides an overview of the role of the circadian cycle in the adaptive immune response. We interrogate the depth of knowledge on cell intrinsic clocks within adaptive immune cells and how these cells may be temporally directed by extrinsic rhythmic signals. We discuss the role of the circadian clock in diseases associated with adaptive immunity such as multiple sclerosis, asthma and parasitic infection. We also discuss the current knowledge on timing of vaccination, and the implications this may have on how we can harness and modulate temporal gating of the adaptive immune response in a clinical setting.

Environmental and genetic risk factors for MS: an integrated review

Recent findings have provided a molecular basis for the combined contributions of multifaceted risk factors for the onset of multiple sclerosis (MS). MS appears to start as a chronic dysregulation of immune homeostasis resulting from complex interactions between genetic predispositions, infectious exposures, and factors that lead to pro-inflammatory states, including smoking, obesity, and low sun exposure. This is supported by the discovery of gene-environment (GxE) interactions and epigenetic alterations triggered by environmental exposures in individuals with particular genetic make-ups. It is notable that several of these pro-inflammatory factors have not emerged as strong prognostic indicators. Biological processes at play during the relapsing phase of the disease may result from initial inflammatory-mediated injury, while risk factors for the later phase of MS, which is weighted toward neurodegeneration, are not yet well defined. This integrated review of current evidence guides recommendations for clinical practice and highlights research gaps.

The Interaction between Viral and Environmental Risk Factors in the Pathogenesis of Multiple Sclerosis

Multiple sclerosis (MS) is a chronic debilitating inflammatory disease of unknown ethology targeting the central nervous system (CNS). MS has a polysymptomatic onset and is usually first diagnosed between the ages of 20–40 years. The pathology of the disease is characterized by immune mediated demyelination in the CNS. Although there is no clinical finding unique to MS, characteristic symptoms include sensory symptoms visual and motor impairment. No definitive trigger for the development of MS has been identified but large-scale population studies have described several epidemiological risk factors for the disease. This list is a confusing one including latitude, vitamin D (vitD) levels, genetics, infection with Epstein Barr Virus (EBV) and endogenous retrovirus (ERV) reactivation. This review will look at the evidence for each of these and the potential links between these disparate risk factors and the known molecular disease pathogenesis to describe potential hypotheses for the triggering of MS pathology.

Ozone, NO2 and PM10 are associated with the occurrence of multiple sclerosis relapses. Evidence from seasonal multi-pollutant analyses

BACKGROUND

Triggers of multiple sclerosis (MS) relapses are essentially unknown. PM10 exposure has recently been associated with an increased risk of relapses.

OBJECTIVES

We further explore the short-term associations between PM10, NO2, benzene (C6H6), O3, and CO exposures, and the odds of MS relapses' occurrence.

METHODS

Using a case-crossover design, we studied 424 MS patients living in the Strasbourg area, France between 2000 and 2009 (1783 relapses in total). Control days were chosen to be ± 35 days relative to the case (relapse) day. Exposure was modeled through ADMS-Urban software at the census block scale. We consider single-pollutant and multi-pollutant conditional logistic regression models coupled with a distributed-lag linear structure, stratified by season ("hot" vs. "cold"), and adjusted for meteorological parameters, pollen count, influenza-like epidemics, and holidays.

RESULTS

The single-pollutant analyses indicated: 1) significant associations between MS relapse incidence and exposures to NO2, PM10, and O3, and 2) seasonality in these associations. For instance, an interquartile range increase in NO2 (lags 0-3) and PM10 exposure were associated with MS relapse incidence (OR = 1.08; 95%CI: [1.03-1.14] and OR = 1.06; 95%CI: [1.01-1.11], respectively) during the "cold" season (i.e., October-March). We also observed an association with O3 and MS relapse incidence during "hot" season (OR = 1.16; 95%CI: [1.07-1.25]). C6H6 and CO were not significantly related to MS relapse incidence. However, using multi-pollutant models, only O3 remained significantly associated with the odds of relapse triggering during "hot" season.

CONCLUSION

We observed significant single-pollution associations between the occurrence of MS relapses and exposures to NO2, O3 and PM10, only O3 remained significantly associated with occurrence of MS relapses in the multi-pollutant model.