The Effect of Ultraviolet Radiation on Human Viral Infections

Ultraviolet radiation, vitamin D, and COVID-19

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has become pandemic on March 11^th, 2020. COVID-19 has a range of symptoms that includes fever, fatigue, dry cough, aches, and labored breathing to acute respiratory distress and possibly death. Health systems and hospitals have been completely rearranged since March 2020 in order to limit the high rate of virus spreading. Hence, a great debate on deferrable visits and treatments including phototherapy for skin diseases is developing. In particular, as regards phototherapy very few data are currently available regarding the chance to continue it, even if it may be a useful resource for treating numerous dermatological patients. However, phototherapy has an immunosuppressive action possibly facilitating virus infection. In the context of COVID-19 infection risk it is important to pointed out whether sunlight, phototherapy and in particular ultraviolet radiation (UV-R) constitute or not a risk for patients. In this review we aimed to focus on the relationship between UV-R, sunlight, phototherapy, and viral infections particularly focusing on COVID-19.

Possible Roles of Permafrost Melting, Atmospheric Transport, and Solar Irradiance in the Development of Major Coronavirus and Influenza Pandemics

Major pandemics involving respiratory viruses develop semi-regularly and require a large flux of novel viruses, yet their origination is equivocal. This paper explores how natural processes could give rise to this puzzling combination of characteristics. Our model is based on available data regarding the emergence of historic influenzas, early COVID-19 cases and spreading, the microbiome of permafrost, long-distance airborne transport of viruses reaching stratospheric levels, ultraviolet immunosuppression, sunlight variations, weather patterns, Arctic thawing, and global warming. Atmospheric conveyance is supported by hemispheric distribution disparities, ties of COVID-19 cases to air pollution particulate concentrations, and contemporaneous animal infections. The following sequence is proposed: (1) virus emergence after hot Arctic summers, predominantly near solar irradiance maxima or involving wildfires, indicates release of large amounts of ancient viruses during extensive permafrost melting, which are then incorporated in autumn polar air circulation, where cold storage and little sunlight permit survival. (2) Pandemics onset in winter to spring at rather few locations: from climate data on Wuhan, emergence occurs where the North Polar Jet stream hovers while intersecting warmer, moist air, producing rain which deposits particulates with the viral harvest on a vulnerable human population. (3) Spring and summer increases in COVID-19 cases link to high solar irradiance, implicating ultraviolet immune suppression as one means of amplification. (4) Viruses multiplied by infected humans at close range being incorporated in atmospheric circulation explains rapid global spread, periodic case surges (waves), and multi-year durations. Pollution and wind geography affect uptake and re-distribution. Our model can be tested, e.g., against permafrost stored in laboratories as well as Artic air samples, and suggests mitigating actions.

Investigating the Potential for Ultraviolet Light to Modulate Morbidity and Mortality From COVID-19: A Narrative Review and Update

During the COVID-19 (coronavirus disease of 2019) pandemic, researchers have been seeking low-cost and accessible means of providing protection from its harms, particularly for at-risk individuals such as those with cardiovascular disease, diabetes and obesity. One possible way is via safe sun exposure, and/or dietary supplementation with induced beneficial mediators (e.g., vitamin D). In this narrative review, we provide rationale and updated evidence on the potential benefits and harms of sun exposure and ultraviolet (UV) light that may impact COVID-19. We review recent studies that provide new evidence for any benefits (or otherwise) of UV light, sun exposure, and the induced mediators, vitamin D and nitric oxide, and their potential to modulate morbidity and mortality induced by infection with SARS-CoV-2 (severe acute respiratory disease coronavirus-2). We identified substantial interest in this research area, with many commentaries and reviews already published; however, most of these have focused on vitamin D, with less consideration of UV light (or sun exposure) or other mediators such as nitric oxide. Data collected to-date suggest that ambient levels of both UVA and UVB may be beneficial for reducing severity or mortality due to COVID-19, with some inconsistent findings. Currently unresolved are the nature of the associations between blood 25-hydroxyvitamin D and COVID-19 measures, with more prospective data needed that better consider lifestyle factors, such as physical activity and personal sun exposure levels. Another short-coming has been a lack of measurement of sun exposure, and its potential to influence COVID-19 outcomes. We also discuss possible mechanisms by which sun exposure, UV light and induced mediators could affect COVID-19 morbidity and mortality, by focusing on likely effects on viral pathogenesis, immunity and inflammation, and potential cardiometabolic protective mechanisms. Finally, we explore potential issues including the impacts of exposure to high dose UV radiation on COVID-19 and vaccination, and effective and safe doses for vitamin D supplementation.

Solar Ultraviolet Radiation and Vitamin D Deficiency on Epstein-Barr Virus Reactivation: Observational and Genetic Evidence From a Nasopharyngeal Carcinoma-Endemic Population

Background

We investigated the relationship of Epstein-Barr virus viral capsid antigen (EBV VCA-IgA) serostatus with ambient and personal ultraviolet radiation (UVR) and vitamin D exposure.

Methods

Using data from a multicenter case-control study, we included 1026 controls subjects in 2014–2017 in Hong Kong, China. Odds ratios (ORs) and 95% confidence intervals (CIs) of the association between UVR exposure and EBV VCA-IgA (seropositivity vs seronegativity) were calculated using unconditional logistic regression models adjusted for potential confounders.

Results

We observed a large increase in seropositivity of EBV VCA-IgA in association with duration of sunlight exposures at both 10 years before recruitment and age 19–30 years (adjusted OR = 3.59, 95% CI = 1.46–8.77; and adjusted OR = 2.44, 95% CI = 1.04–5.73 for ≥8 vs <2 hours/day; P for trend = .005 and .048, respectively). However, no association of EBV VCA-IgA serostatus with other indicators of UVR exposure was found. In addition, both circulating 25-hydroxyvitamin D (25OHD) and genetic predicted 25OHD were not associated with EBV VCA-IgA serostatus.

Conclusions

Our results suggest that personal UVR exposure may be associated with higher risk of EBV reactivation, but we did not find clear evidence of vitamin D exposure (observational or genetic), a molecular mediator of UVR exposure. Further prospective studies in other populations are needed to confirm this finding and to explore the underlying biological mechanisms. Information on photosensitizing agents, and serological markers of EBV, and biomarkers related to systemic immunity and inflammation should be collected and are also highly relevant in future studies.

Balance between Health Risks and Benefits for Outdoor Workers Exposed to Solar Radiation: An Overview on the Role of Near Infrared Radiation Alone and in Combination with Other Solar Spectral Bands

Near infrared or infrared A (IRA) accounts for over 40% of the solar spectrum (SS) and is able to reach subcutaneous tissue as well as the retina. Outdoor workers are occupationally exposed to solar radiation (SR), but the level of exposure may differ widely depending on the job performed, time spent outdoors, latitude, altitude, season, personal protection, etc. Until now, risk assessment and management for outdoor workers has focused on the prevention of both acute and long-term effects on the eye and the skin due to solar ultraviolet radiation (UVR) with little consideration of the other components of the SS (a possible exception is represented by visible radiation with reference to the eye). A growing body of evidence coming from in vitro studies indicates that IRA is involved in cellular reactive oxygen species (ROS) production and may interfere with the respiratory chain in the mitochondria. Moreover, it can modulate gene expression and some metabolic pathways. The biological action of IRA is only partly attributable to a thermal mechanism, should it be also involved in photochemical ones. The cellular and molecular pathways affected by IRA are partly similar and partly different with respect to those involved in the case of visible ultraviolet A (UVA) and ultraviolet B (UVB) radiation. Consequently, the net effect of the SS is very difficult to predict at different levels of the biological organization, making more difficult the final balance of health risk and benefits (for the skin, eye, immune system, blood pressure, etc.) in a given exposure situation. Moreover, few in vivo studies and no epidemiological data are presently available in this regard. Investigating this topic may contribute to better defining the individual exposome. More practically, it is expected to bring benefits to the risk assessment and management for outdoor workers exposed to SS, contributing to: (1) better definition of the individual profiles of susceptibility, (2) more focused preventive and protective measures, (3) better implementation of the health surveillance and (4) a more effective information and training.

Ultraviolet Radiation Exposure and the Risk of Herpes Zoster in Three Prospective Cohort Studies

OBJECTIVE

To examine the association between ultraviolet radiation (UVR) exposure and the risk of herpes zoster (HZ) in 3 prospective cohorts.

PATIENTS AND METHODS

We included 205,756 participants from the Health Professionals Follow-up Study (HPFS; 1986-2008), Nurses' Health Study (NHS; 1996-2012), and Nurses' Health Study II (NHS II; 1991-2013). Ambient UVR exposure was based on updated geocoded address histories linked with a high-resolution spatiotemporal ultraviolet model. Incident HZ cases were identified by self-reported clinician diagnosis. Sunburn history and medical, lifestyle, and dietary factors were assessed using biennial questionnaires. Multivariable Cox proportional hazards models were used.

RESULTS

A total of 24,201 cases of HZ occurred during 3,626,131 person-years. Ambient UVR exposure was associated with a higher risk of HZ in men (HPFS: multivariable-adjusted hazard ratio [MVHR] comparing highest vs lowest quintiles, 1.14; 95% CI, 1.02-1.29; P=.03 for trend) but not in women (NHS: MVHR, 0.99; 95% CI, 0.93-1.05; NHS II: MVHR, 0.96; 95% CI, 0.90-1.03). A higher lifetime number of severe sunburns was associated with a higher risk of HZ in all cohorts (HPFS: MVHR for ≥10 sunburns vs none, 1.08; 95% CI, 0.96-1.20; P=.02 for trend; NHS: MVHR, 1.14; 95% CI, 1.05-1.22; P=.01 for trend; NHS II: MVHR, 1.13; 95% CI, 1.00-1.28; P<.001 for trend).

CONCLUSION

Ambient UVR exposure was associated with a higher risk of HZ in men but not in women. A history of severe sunburn was associated with a modest increased risk of HZ in men and women, possibly because of immunosuppression from overexposure to the sun.

A Novel In Vivo Infection Model To Study Papillomavirus-Mediated Disease of the Female Reproductive Tract

Papillomaviruses exhibit species-specific tropism, thereby limiting understanding and research of several aspects of HPV infection and carcinogenesis. The discovery of a murine papillomavirus (MmuPV1) provides the opportunity to study papillomavirus infections in a tractable, in vivo laboratory model. MmuPV1 infects and causes disease in the cutaneous epithelium, as well as the mucosal epithelia of the oral cavity and anogenital tract. In this report, we describe a murine model of MmuPV1 infection and neoplastic disease in the female reproductive tracts of wild-type immunocompetent FVB mice. Low-grade dysplastic lesions developed in reproductive tracts of FVB mice infected with MmuPV1 for 4 months, and mice infected for 6 months developed significantly worse disease, including squamous cell carcinoma (SCC). We also tested the contribution of estrogen and/or UV radiation (UVR), two cofactors we previously identified as being involved in papillomavirus-mediated disease, to cervicovaginal disease. Similar to HPV16 transgenic mice, exogenous estrogen treatment induced high-grade precancerous lesions in the reproductive tracts of MmuPV1-infected mice by 4 months and together with MmuPV1 efficiently induced SCC by 6 months. UV radiation and exogenous estrogen cooperated to promote carcinogenesis in MmuPV1-infected mice. This murine infection model represents the first instance of de novo papillomavirus-mediated carcinogenesis in the female reproductive tract of wild-type mice resulting from active virus infection and is also the first report of the female hormone estrogen contributing to this process. This model will provide an additional platform for fundamental studies on papillomavirus infection, cervicovaginal disease, and the role of cellular cofactors during papillomavirus-induced carcinogenesis.IMPORTANCE Tractable and efficient models of papillomavirus-induced pathogenesis are limited due to the strict species-specific and tissue-specific tropism of these viruses. Here, we report a novel preclinical murine model of papillomavirus-induced cervicovaginal disease in wild-type, immunocompetent mice using the recently discovered murine papillomavirus, MmuPV1. In this model, MmuPV1 establishes persistent viral infections in the mucosal epithelia of the female reproductive tract, a necessary component needed to accurately mimic HPV-mediated neoplastic disease in humans. Persistent MmuPV1 infections were able to induce progressive neoplastic disease and carcinogenesis, either alone or in combination with previously identified cofactors of papillomavirus-induced disease. This new model will provide a much-needed platform for basic and translational studies on both papillomavirus infection and associated disease in immunocompetent mice.

A time for everything and everything in its time - exploring the mechanisms underlying seasonality of COPD exacerbations

Across Europe, COPD affects 23 million people leading to annual health care costs of ~€25.1 billion. This burden is particularly severe during winter months in association with the peak incidence of exacerbation events. Seasonal variation in the health status of patients with COPD places additional and often critical pressure on already strained health care resources. COPD exacerbations are characterized by worsening day-to-day symptoms of an individual and often triggered by respiratory infections, but the process by which this occurs in a seasonal fashion is likely to be multifactorial. In this review, we discuss recent population studies that highlight the impact of seasonality in COPD and review the proposed biological mechanisms underlying this. An appraisal of the role of the host susceptibility and response, environmental triggers and the biology of respiratory pathogens is detailed. The impact of each aspect is considered, and an integrated model of the context for the whole individual and society in general is explored.

Rodent Papillomaviruses

Preclinical infection model systems are extremely valuable tools to aid in our understanding of Human Papillomavirus (HPV) biology, disease progression, prevention, and treatments. In this context, rodent papillomaviruses and their respective infection models are useful tools but remain underutilized resources in the field of papillomavirus biology. Two rodent papillomaviruses, MnPV1, which infects the Mastomys species of multimammate rats, and MmuPV1, which infects laboratory mice, are currently the most studied rodent PVs. Both of these viruses cause malignancy in the skin and can provide attractive infection models to study the lesser understood cutaneous papillomaviruses that have been frequently associated with HPV-related skin cancers. Of these, MmuPV1 is the first reported rodent papillomavirus that can naturally infect the laboratory strain of mice. MmuPV1 is an attractive model virus to study papillomavirus pathogenesis because of the ubiquitous availability of lab mice and the fact that this mouse species is genetically modifiable. In this review, we have summarized the knowledge we have gained about PV biology from the study of rodent papillomaviruses and point out the remaining gaps that can provide new research opportunities.

Ultraviolet Radiation and Kaposi Sarcoma Incidence in a Nationwide US Cohort of HIV-Infected Men

Background

Although ultraviolet radiation (UVR) is established as both an inducer of herpes simplex virus reactivation and as the primary risk factor for many common skin cancers, its relationship with human herpes virus 8 (HHV8) infection or risk of Kaposi sarcoma (KS) is unknown.

Methods

Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for the association between ambient UVR, history of nonmelanoma skin cancer (NMSC; as a biomarker of personal cumulative UVR dose), and incidence of first primary KS in a nationwide US cohort of white and African American male veterans infected with HIV between 1986 and 1996 (prior to the widespread availability of treatment) using Cox regression. All statistical tests were two-sided.

Results

Based on discharge records, there were 422 newly diagnosed KS cases among 17 597 HIV-infected veterans. Cohort members with prior NMSC had a statistically significantly increased risk of KS (HR = 8.64, 95% CI = 6.23 to 11.96) in the total population. Risk of KS was higher for quartile 4 vs 1 among the total population (HR = 1.49, 95% CI = 1.02 to 2.16, P_trend UVR quartile [coded 1 to 4] = .02) and among whites (HR = 1.75, 95% CI = 1.11 to 2.78, P_trend = .009), but not among African Americans (HR = 1.23, 95% CI = 0.71 to 2.15, P_trend = .23).

Conclusions

KS risk was elevated among HIV-infected men with NMSC diagnosis and in those living in locations with high ambient UVR at time of HIV diagnosis. Our novel findings suggesting that UVR exposure may increase KS risk warrant further investigation.

UV "Indices"-What Do They Indicate?

Ultra-Violet (UV) radiation covers the spectrum of wavelengths from 100 to 400 nm. The potency and biological activity for a variety of endpoints differ by wavelength. For monitoring and communication purposes, different UV action spectra have been developed. These spectra use different weighting functions. The action spectrum for erythemal dose is the most widely used one. This erythemal dose per time or dose-rate has been further simplified into a “UV index”. Following this example, in our review we use the term “index” or (plural) “indices” in a more general description for all simplified single-value measures for any biologically effective UV dose, e.g., for human non-melanoma skin cancer and for previtamin D production rate. Ongoing discussion about the existence of an increased melanoma risk due to UV-A exposure underscores the uncertainties inherent in current weighting functions. Thus, we performed an online literature search to review the data basis for these indices, to understand their relevance for an individual, and to assess the applicability of the indices for a range of exposure scenarios. Even for natural (solar) UV, the spectral composition varies spatially and temporally. Artificial UV sources and personal protection introduce further variation to the spectral composition. Many biological effects are proposed for UV radiation. Only few endpoints have been studied sufficiently to estimate a reliable index. Weighting functions for chronic effects and most importantly for cancer endpoints have been developed in animal models, and often for proxy endpoints only. Epidemiological studies on biological effects of UV radiation should not only depend on single-value weighted UV dose estimates (indexes) but should strive for a more detailed description of the individual exposure. A better understanding of the adverse and beneficial effects of UV radiation by wavelength would also improve medical counseling and health communication regarding individual health-supportive behavior.

The Skin Microbiome: Is It Affected by UV-induced Immune Suppression?

Human skin apart from functioning as a physical barricade to stop the entry of pathogens, also hosts innumerable commensal organisms. The skin cells and the immune system constantly interact with microbes, to maintain cutaneous homeostasis, despite the challenges offered by various environmental factors. A major environmental factor affecting the skin is ultraviolet radiation (UV-R) from sunlight. UV-R is well known to modulate the immune system, which can be both beneficial and deleterious. By targeting the cells and molecules within skin, UV-R can trigger the production and release of antimicrobial peptides, affect the innate immune system and ultimately suppress the adaptive cellular immune response. This can contribute to skin carcinogenesis and the promotion of infectious agents such as herpes simplex virus and possibly others. On the other hand, a UV-established immunosuppressive environment may protect against the induction of immunologically mediated skin diseases including some of photodermatoses such as polymorphic light eruption. In this article, we share our perspective about the possibility that UV-induced immune suppression may alter the landscape of the skin’s microbiome and its components. Alternatively, or in concert with this, direct UV-induced DNA and membrane damage to the microbiome may result in pathogen associated molecular patterns (PAMPs) that interfere with UV-induced immune suppression.

Increasing Incidence of Herpes Zoster Over a 60-year Period From a Population-based Study

BACKGROUND

Temporal increases in the incidence of herpes zoster (HZ) have been reported but studies have examined short study periods, and the cause of the increase remains unknown. We examined the long-term trend of HZ.

METHODS

A population-based cohort study was conducted in Olmsted County, Minnesota, using data from 1945-1960 and 1980-2007. Medical records review of possible cases was performed to confirm incident cases of HZ, the patient's immune status, and prescribing of antivirals for HZ. We examined the relative change in the temporal trend in the incidence rates before and after the introduction of the varicella vaccination program.

RESULTS

Of the 8017 patients with HZ, 58.7% were females and 6.6% were immunocompromised. The age- and sex-adjusted incidence rate of HZ increased from 0.76 per 1000 person-years (PY) (95% confidence interval [CI], .63-.89) in 1945-1949 to 3.15 per 1000 PY (95% CI, 3.04-3.26) in 2000-2007. The rate of increase across the time period was 2.5% per year after adjusting for age and sex (adjusted incidence rate ratio, 1.025 [95% CI, 1.023-1.026]; P < .001). The incidence of HZ significantly increased among all age groups and both sexes. We found no change in the rate of increase before vs after the introduction of the varicella vaccination program.

CONCLUSIONS

The incidence of HZ has increased >4-fold over the last 6 decades. This increase is unlikely to be due to the introduction of varicella vaccination, antiviral therapy, or change in the prevalence of immunocompromised individuals.

Effects of meteorologic factors and schooling on the seasonality of group A streptococcal pharyngitis

The objective of this study was to determine the seasonal pattern of group A streptococcal pharyngitis in children attended at a hospital emergency department in the Mediterranean island of Mallorca (Spain), and its association with meteorologic factors and schooling. We conducted a retrospective review of the medical records of children aged 1-15 years with a diagnosis of Streptococcus pyogenes pharyngitis between January 2006 and December 2011. The number of S. pyogenes pharyngitis was correlated to temperature, humidity, rainfall, atmospheric pressure, wind speed, solar radiation, and schooling, using regression and time series techniques. A total of 906 patients (median, 4 years old) with S. pyogenes pharyngitis, confirmed by throat culture, were attended during the study period. A seasonal pattern was observed with a peak activity in June and a minimum in September. Mean temperature, solar radiation, and school holidays were the best predicting variables (R(2) = 0.68; p < 0.001). S. pyogenes activity increased with the decrease of mean temperature (z = -2.4; p < 0.05), the increase of solar radiation (z = 4.2; p < 0.001), and/or the decrease in school holidays (z = -2.4; p < 0.05). In conclusion, S. pyogenes pharyngitis had a clear seasonality predominating in springtime, and an association with mean temperature, solar radiation, and schooling was observed. The resulting model predicted 68 % of S. pyogenes pharyngitis.

A prospective study of the clinical characteristics of patients with herpes simplex and varicella zoster keratitis, presenting to a New Zealand emergency eye clinic

PURPOSE

To identify the demographic and clinical associations of patients presenting with herpetic keratitis in New Zealand compared with presentations of presumed microbial keratitis.

METHODS

A prospective, 6-month, observational case series of presumed microbial keratitis (including marginal keratitis), specifically identifying all cases of herpes simplex and varicella zoster keratitis attending an emergency eye clinic was conducted. Main outcome measures included demographics, presenting signs and symptoms, and medical, ocular, and drug history.

RESULTS

A total of 140 cases of herpetic keratitis were identified, which comprised 125 cases of herpes simplex virus (89%) and 15 cases of varicella zoster virus (11%). Herpes simplex keratitis was associated with a history of keratitis (n = 58, phi = 0.24, P < 0.0001), Maori ethnicity (n = 27, phi = 0.26, P < 0.0001), respiratory disease (n = 18, phi = 0.14, P = 0.009), corticosteroid use (n = 23, phi = 0.22, P < 0.0001), and cardiovascular disease (CVD) (n = 10, phi = 0.11, P = 0.03). Inverse association was observed between herpes simplex keratitis and ocular surface disease (n = 8, phi = -0.16, P < 0.002) and Asian ethnicity (n = 4, phi = -0.11, P = 0.04). Varicella zoster keratitis was associated with CVD (n = 3, phi = 0.15, P = 0.03).

CONCLUSIONS

Patients with asthma, CVD, on long-term corticosteroid inhalers or creams, or of Maori ethnicity need particular assessment to investigate herpes simplex as a possible cause of keratitis. Clinicians prescribing inhaled corticosteroids or topical corticosteroid creams should be aware of possible association with herpes simplex keratitis.

[Evaluation of in vitro efficacy of combined riboflavin and ultraviolet-A (365 nm) for Acanthamoeba]

INTRODUCTION

Acanthamoeba keratitis is a rare but serious disease and is particularly difficult to treat when the diagnosis is delayed, partly because of the limitations of current therapies. The purpose of our study is to evaluate the anti-amoebic effectiveness of riboflavin and UV-A on Acanthamoeba castellani.

MATERIALS AND METHODS

We tested the effect of 0.02% chlorhexidine alone (C), the combination of riboflavin 1% and UV-A (UV-A+R), and the combination of the two treatments (R+C+UV-A) on cultures of vegetative and cystic forms of A. castellani. We conducted a parasite count under optical microscopy for each treated area at day 1, 4 and 8.

RESULTS

There was a decrease in the number of cysts for all three treatments (C, UV-A+R, R+C+UV-A). This reduction was greater for the plates treated with R+UV-A (P <0.01 at D8) and those treated with C+R+UV-A (P<0.001 at D8) compared to those exposed to chlorhexidine alone (C). There was no decrease in the number of amoebic trophozoites for the three treatments (C, UV-A+R, R+C+UV-A), but encystment was observed.

DISCUSSION

Given the in vitro efficacy of riboflavin combined with UV-A against cystic forms of A. castellani and excellent in vivo tolerance of the procedure, the treatment of acanthamoeba keratitis might be improved by this new therapeutic approach.

Will Global Climate Change Alter Fundamental Human Immune Reactivity: Implications for Child Health?

The human immune system is an interface across which many climate change sensitive exposures can affect health outcomes. Gaining an understanding of the range of potential effects that climate change could have on immune function will be of considerable importance, particularly for child health, but has, as yet, received minimal research attention. We postulate several mechanisms whereby climate change sensitive exposures and conditions will subtly impair aspects of the human immune response, thereby altering the distribution of vulnerability within populations-particularly for children-to infection and disease. Key climate change-sensitive pathways include under-nutrition, psychological stress and exposure to ambient ultraviolet radiation, with effects on susceptibility to infection, allergy and autoimmune diseases. Other climate change sensitive exposures may also be important and interact, either additively or synergistically, to alter health risks. Conducting directed research in this area is imperative as the potential public health implications of climate change-induced weakening of the immune system at both individual and population levels are profound. This is particularly relevant for the already vulnerable children of the developing world, who will bear a disproportionate burden of future adverse environmental and geopolitical consequences of climate change.

Solar radiation and water vapor pressure to forecast chickenpox epidemics

The clear seasonality of varicella infections in temperate regions suggests the influence of meteorologic conditions. However, there are very few data on this association. The aim of this study was to determine the seasonal pattern of varicella infections on the Mediterranean island of Mallorca (Spain), and its association with meteorologic conditions and schooling. Data on the number of cases of varicella were obtained from the Network of Epidemiologic Surveillance, which is composed of primary care physicians who notify varicella cases on a compulsory basis. From 1995 to 2012, varicella cases were correlated to temperature, humidity, rainfall, water vapor pressure, atmospheric pressure, wind speed, and solar radiation using regression and time-series models. The influence of schooling was also analyzed. A total of 68,379 cases of varicella were notified during the study period. Cases occurred all year round, with a peak incidence in June. Varicella cases increased with the decrease in water vapor pressure and/or the increase of solar radiation, 3 and 4 weeks prior to reporting, respectively. An inverse association was also observed between varicella cases and school holidays. Using these variables, the best fitting autoregressive moving average with exogenous variables (ARMAX) model could predict 95 % of varicella cases. In conclusion, varicella in our region had a clear seasonality, which was mainly determined by solar radiation and water vapor pressure.

Are hospitalizations for rotavirus gastroenteritis associated with meteorologic factors?

Local climatic factors might explain seasonal patterns of rotavirus infections, but few models have been proposed to determine the effects of weather conditions on rotavirus activity. Here, we study the association of meteorologic factors with rotavirus activity, as determined by the number of children hospitalized for rotavirus gastroenteritis on the Mediterranean island of Mallorca (Spain). We conducted a retrospective review of the medical records of children aged 0-5 years admitted for rotavirus gastroenteritis between January 2000 and December 2010. The number of rotavirus hospitalizations was correlated to temperature, humidity, rainfall, atmospheric pressure, water vapor pressure, wind speed, and solar radiation using regression and time-series techniques. A total of 311 patients were hospitalized for rotavirus gastroenteritis in the 11-year study period, with a seasonal pattern from December to June, and a peak incidence in February. After multiple regressions, weekly rotavirus activity could be explained in 82 % of cases (p < 0.001) with a one-week lag meteorologic model. Rotavirus activity was negatively associated to temperature and positively associated to atmospheric pressure, solar radiation, and wind speed. Temperature and solar radiation were the factors that contributed most to the model, with a peak rotavirus activity at 9 °C and 800 10KJ/m(2), respectively. In conclusion, hospitalization for rotavirus was strongly associated with mean temperature, but an association of rotavirus activity with solar radiation, atmospheric pressure, and wind speed was also demonstrated. This model predicted more than 80 % of rotavirus hospitalizations.

Association between unprotected ultraviolet radiation exposure and recurrence of ocular herpes simplex virus

Studies have suggested that exposure to ultraviolet (UV) light may increase risk of herpes simplex virus (HSV) recurrence. Between 1993 and 1997, the Herpetic Eye Disease Study (HEDS) randomized 703 participants with ocular HSV to receipt of acyclovir or placebo for prevention of ocular HSV recurrence. Of these, 308 HEDS participants (48% female and 85% white; median age, 49 years) were included in a nested study of exposures thought to cause recurrence and were followed for up to 15 months. We matched weekly UV index values from the National Oceanic and Atmospheric Administration to each participant's study center and used marginal structural Cox models to account for time-varying psychological stress and contact lens use and selection bias from dropout. There were 44 recurrences of ocular HSV, yielding an incidence of 4.3 events per 1,000 person-weeks. Weighted hazard ratios comparing persons with ≥8 hours of time outdoors to those with less exposure were 0.84 (95% confidence interval (CI): 0.27, 2.63) and 3.10 (95% CI: 1.14, 8.48) for weeks with a UV index of <4 and ≥4, respectively (ratio of hazard ratios = 3.68, 95% CI: 0.43, 31.4). Though results were imprecise, when the UV index was higher (i.e., ≥4), spending 8 or more hours per week outdoors was associated with increased risk of ocular HSV recurrence.

The challenges of UV-induced immunomodulation for children's health

Exposure to solar ultraviolet radiation (UVR) is recognised to have both beneficial and harmful effects on human health. With regard to immune responses, it can lead to suppression of immunity and to the synthesis of vitamin D, a hormone that can alter both innate and adaptive immunity. The consequences in children of such UV-induced changes are considerable: first there are positive outcomes including protection against some photoallergic (for example polymorphic light eruption) and T cell-mediated autoimmune diseases (for example multiple sclerosis) and asthma, and secondly there are negative outcomes including an increased risk of skin cancer (squamous cell carcinoma, basal cell carcinoma and cutaneous malignant melanoma) and less effective control of several infectious diseases. Many uncertainties remain regarding the amount of sun exposure that would provide children with the most effective responses against the variety of immunological challenges that they are likely to experience.

Modulation of the immune system by UV radiation: more than just the effects of vitamin D?

Humans obtain most of their vitamin D through the exposure of skin to sunlight. The immunoregulatory properties of vitamin D have been demonstrated in studies showing that vitamin D deficiency is associated with poor immune function and increased disease susceptibility. The benefits of moderate ultraviolet (UV) radiation exposure and the positive latitude gradients observed for some immune-mediated diseases may therefore reflect the activities of UV-induced vitamin D. Alternatively, other mediators that are induced by UV radiation may be more important for UV-mediated immunomodulation. Here, we compare and contrast the effects of UV radiation and vitamin D on immune function in immunopathological diseases, such as psoriasis, multiple sclerosis and asthma, and during infection.

The consequences of UV-induced immunosuppression for human health

Exposure to UV radiation can cause suppression of specific immune responses. The pathways leading to the down-regulation are complex, starting from the absorption of UV photons by chromophores in the skin and ending with local and systemic changes in immune mediators, the generation of T and B regulatory cells and inhibition of effector and memory T cell activation. The consequences for human health are thought to be both beneficial and adverse. The former are illustrated by protection against polymorphic light eruption, and possible protection against T cell-mediated autoimmune diseases and asthma. The latter are illustrated by skin cancer, cutaneous lupus erythematosus and infectious diseases including vaccination. Many outstanding questions remain in this rapidly developing and controversial area, not least what advice to give the general public regarding their sun exposure. While considerable advances have been made in the development of strategies that preserve the health benefits of sunlight exposure and decrease its detrimental effects, further research is required before optimal levels of protection are achieved.

Effect of season of inoculation on immune response to rubella vaccine in children

The yearly seasons are marked by changes in the amount of sunlight. Ultraviolet radiation (UVR) is known to adversely affect the course of viral infections, immunologic memory and cellular and humoral immune responses. Our objectives were to investigate potential differences in the immune response of the rubella vaccine after 3-4 years by season of inoculation. Children aged 4-5 years attending four kindergartens in villages in northern Israel, all of whom had been vaccinated at 1 year of age, were enrolled in the study. Participants were divided into three groups by season of the year in which the inoculation was performed: summer (N = 63), winter (N = 36) and intermediate (N = 104). Main outcome measures were mean geometrical titer of rubella antibodies and complete, partial or no immunity to rubella by season of inoculation. Of the 203 children tested, 186 (91.6%) had adequate antibody levels, 7 (3.4%) had equivocal levels and 10 (4.9%) had inadequate levels. Significantly higher mean geometrical titers were found in the winter-inoculated compared with the summer-inoculated group (73.0 ± 2.6 vs 47.6 ± 2.8; p < 0.05). The same tendency was noted in the percent of infants properly immunized. This preliminary study shows a strong correlation between the immune response to rubella vaccine and the season of vaccination. Immunogenicity may be improved by inoculating children during seasons of less sunlight or by reducing the children's exposure to sunlight following inoculation. This practice is especially important in areas with extreme seasonal variability in solar radiation and tropical areas. Further studies are needed to corroborate and expand these findings.

Ultraviolet radiation and immunosuppression

Ultraviolet (UV) radiation is a complete carcinogen. The effects of UV radiation are mediated via direct damage to cellular DNA in the skin and suppression of image surveillance mechanisms. In the context of organ transplantation, addiction of drugs which suppress the immune system add greatly to the carcinogenicity of UV radiation. This review considers the mechanisms of such effects.

Genome-wide identification of susceptibility alleles for viral infections through a population genetics approach

Viruses have exerted a constant and potent selective pressure on human genes throughout evolution. We utilized the marks left by selection on allele frequency to identify viral infection-associated allelic variants. Virus diversity (the number of different viruses in a geographic region) was used to measure virus-driven selective pressure. Results showed an excess of variants correlated with virus diversity in genes involved in immune response and in the biosynthesis of glycan structures functioning as viral receptors; a significantly higher than expected number of variants was also seen in genes encoding proteins that directly interact with viral components. Genome-wide analyses identified 441 variants significantly associated with virus-diversity; these are more frequently located within gene regions than expected, and they map to 139 human genes. Analysis of functional relationships among genes subjected to virus-driven selective pressure identified a complex network enriched in viral products-interacting proteins. The novel approach to the study of infectious disease epidemiology presented herein may represent an alternative to classic genome-wide association studies and provides a large set of candidate susceptibility variants for viral infections.

Viruses have represented a constant threat to human communities throughout their history, therefore, human genes involved in anti-viral response can be thought of as targets of virus-driven selective pressure. Here we utilized the marks left by selection to identify viral infection-associated allelic variants. We analyzed more than 660,000 single nucleotide polymorphisms (SNPs) genotyped in 52 human populations, and we used virus diversity (the number of different viruses in a geographic region) to measure virus-driven selective pressure. Results showed that genes involved in immune response and in the biosynthesis of glycan structures functioning as viral receptors display more variants associated with virus diversity than expected by chance. The same holds true for genes encoding proteins that directly interact with viral components. Genome-wide analysis identified 441 variants, mapping to 139 human genes, significantly associated with virus-diversity. We analyzed the functional relationships among genes subjected to virus-driven selective pressure and identified a complex interaction network enriched in viral products-interacting proteins. Therefore, we describe a novel approach for the identification of gene variants that may be involved in the susceptibility to viral infections.

The dark and the sunny sides of UVR-induced immunosuppression: photoimmunology revisited

Immunosuppression induced by solar UVR is regarded as one of the major negative impacts of sunlight on human health. Despite this immunosuppression, bacterial superinfections are rarely observed after UVR exposure. A possible explanation for this seeming paradox may be that although it suppresses T-cell-mediated immune reactions, UVR induces the release of cutaneous antimicrobial peptides--an essential component of the innate immune system. The "sunshine vitamin," vitamin D, also appears to be involved, as UVR suppresses the adaptive but induces the innate immune response. T cells in the skin are the critical cellular mediators of the vast majority of inflammatory dermatoses, and thus probably more harmful than beneficial. Hence, it is tempting to speculate that a certain and constant level of immunosuppression by physiological UVR doses might be beneficial, taming overshooting immune reactions. At the same time, by inducing antimicrobial peptides, these low UVR doses may foster the antibacterial defense. Thus, suppression of the adaptive and induction of the innate immune system by UVR may be components of a physiological protection process. These insights might have effect on the future recommendations for daily sun protection.