Health effects of static magnetic fields--a review of the epidemiological evidence

Potential health effects of static magnetic fields have received far less attention than, for example, power frequency or radiofrequency fields. Static fields are found in certain occupational settings, e.g. in the aluminium and chloralkali industries, in arc-welding processes, and certain railways systems. Magnetic resonance imaging (MRI) for medical diagnosis is another source. This paper summarizes the epidemiological evidence of static magnetic field exposure and long-term health effects. There are only a few epidemiological studies available, and the majority of these have focused on cancer risks. There are some reports on reproductive outcomes, and sporadic studies of other outcomes. Overall, few occupational studies have focused specifically on effects of static magnetic field exposure, and exposure assessment have consequently been poor or non-existent. Results from studies that have estimated static magnetic field exposure have not indicated any increased cancer risks, but they are generally based on small numbers of cases and crude exposure assessment. Control of confounding has been limited, and it is likely that the “healthy worker” effect have influenced the results. A few studies have reported results on reproductive outcomes among aluminium workers and MRI operators, but limitations in study designs prevent conclusions. A problem in epidemiological studies of static magnetic fields is that workers in exposed occupations are also exposed to a wide variety of other potentially harmful agents, including some known carcinogens. In conclusion, the available evidence from epidemiological studies is not sufficient to draw any conclusions about potential health effects of static magnetic field exposure.     

Linking within- and between-host dynamics in the evolutionary epidemiology of infectious diseases

Nested models (also called embedded models) explicitly link dynamical processes that occur at different scales. Recently there has been considerable interest in linking within- and between-host levels of disease dynamics in the study of pathogen evolution. Here we review the extent to which these nested models have increased our understanding of pathogen evolution. We suggest that, although such models have been useful for determining the nature of tradeoffs between epidemiological parameters and for evaluating the consequences of conflicting selection pressures at different scales, the vast majority of previous results could likely have been obtained without the use of nested models per se. Nevertheless, these models have proven very useful through their highlighting of the importance of within-host disease dynamics on pathogen evolution.     

Dissecting cause and effect in the pathogenesis of psychiatric disorders: genes, environment and behaviour

It has long been established that the development of psychiatric illness results from a complex interplay between genetic and environmental factors. Postmortem and genetic linkage studies have identified a number of promising candidate genes which have been reinforced by replication and functional studies. However, the fact that concordance rates for monozygotic twins rarely approach 100% highlights the involvement of environmental factors. Whilst epidemiological studies of psychiatric cohorts have demonstrated potential risk factors, such studies are clearly limited and in many cases the potential mechanism linking a given risk factor with pathogenesis remains unclear. A very powerful method of elucidating the mechanisms underlying gene-environment interactions is the use of appropriate animal models of psychiatric pathology. Whilst animals cannot be used to map the entire complexity of diseases such as schizophrenia, dissecting the symptom profile into more simply encapsulated traits or endophenotypes has proved to be a successful approach. Such endophenotypes provide a measurable link between aetiological factors and phenotypic outcome. Given the potential for the careful control and modification of an experimental animal's environment, the combination of studies of candidate genes with investigations of environmental factors is an effective heuristic tool, allowing examination of behavioural endophenotypes in conjunction with cellular and molecular outcomes. This review will consider the extant genetic, molecular, pharmacological and lesion-based models of psychiatric disorders, and the relevant methods of environmental manipulation appearing in the literature. We will discuss studies where such models have been combined, and the potential for future experimentation in this area.     

Analysis of continuous covariables in epidemiological studies: Dose‐response modelling and confounder adjustment

The analysis of continuous covariables with regression models commonly used in epidemiology are reviewed and compared. While some methods have been in use for decades, other more recent methods are not yet common or have not yet been formally described. It is shown that recently developed methods such as fractional polynomials and others are very useful to obtain dose‐response curves or for confounder adjustment. Different methods have their specific merits making it difficult to give general recommendations. The application of some of the methods is demonstrated with real data examples from epidemiological studies. Some suggestions for practical strategies in analysing continuous covariables are given.     

Comparison of three different ways of measuring distances between residences and high voltage power lines

The aim of this study was to evaluate whether distance data based on calculations by use of digitalized geographical information systems (GIS) and distance data based on measurements on 1:5000 maps agree sufficiently with on site distance measurements to be used as input to magnetic field calculations in epidemiological studies. The analysis were performed by use of weighted kappa (kappa(w)) statistical method described by Bland and Altman for comparison of measures of agreement. Map measurements showed better agreement with on site measurements than GIS calculations did. However, we consider both methods appropriate for use in larger epidemiological studies if the results are interpreted with caution. GIS calculations have the advantage of being both time and cost saving.     

Patterns in parasite epidemiology: the peak shift

A characteristic relationship between infection and host age, with levels of infection reaching a peak in particular age classes, has been reported for many parasites. However, several field studies have shown that this relationship is not invariant: if age-infection data are compared across host populations, the peak level of infection is higher and occurs at a younger age when the transmission rate is high, and is lower and occurs at an older age when it is low. This pattern is called the ;peak shift'. Here, Mark Woolhouse reviews the evidence for and the implications of the peak shift. The peak shift is consistent with the predictions of mathematical models that assume gradually acquired protective immunity, and this interpretation is supported by experimental studies using animals. This agreement between theory, experimental evidence and field studies strongly suggests that acquired immunity has a major impact on epidemiological patterns not only for parasites such as malaria, where the importance of acquired immunity is not in doubt, but also for many parasitic helminths, where the role of acquired immunity is less widely accepted.     

Epidemiology of insect-transmitted plant viruses: modelling disease dynamics and control interventions

Abstract. Plant viruses are an important constraint to crop production world‐wide. Rarely have plant virologists, vector entomologists and crop specialists worked together in search of sustainable management practices for viral diseases. Historically, modelling approaches have been vector‐based dealing with empirical forecasting systems or simulation of vector population dynamics. More recently, epidemiological models, such as those used in human/animal epidemiology, have been introduced in an attempt to characterize and analyse the population ecology of viral diseases. The theoretical bases for these models and their use in evaluating control strategies in terms of the interactions between host, virus and vector are considered here. Vector activity and behaviour, especially in relation to virus transmission, are important determinants of the rate and extent of epidemic development. The applicability and flexibility of these models are illustrated by reference to specific case studies, including the increasing importance of whitefly‐transmitted viruses. Some outstanding research and methodological issues are considered.     

Environmental chemical mediated male reproductive toxicity: Drosophila melanogaster as an alternate animal model

Industrialization and indiscriminate use of agrochemicals have increased the human health risk. Recent epidemiological studies raised a concern for male reproduction given their observations of reduced sperm counts and altered semen quality. Interestingly, environmental factors that include various metals, pesticides and their metabolites have been causally linked to such adversities by their presence in the semen at levels that correlate to infertility. The epidemiological observations were further supported by studies in animal models involving various chemicals. Therefore, in this review, we focused on male reproductive toxicity and the adverse effects of different environmental chemicals on male reproduction. However, it is beyond the scope of this review to provide a detailed appraisal of all of the environmental chemicals that have been associated with reproductive toxicity in animals. Here, we provided the evidence for reproductive adversities of some commonly encountered chemicals (pesticides/metals) in the environment. In view of the recent thrust for an alternate to animal models in research, we subsequently discussed the contributions of Drosophila melanogaster as an alternate animal model for quick screening of toxicants for their reproductive toxicity potential. Finally, we emphasized the genetic and molecular tools offered by Drosophila for understanding the mechanisms underlying the male reproductive toxicity.     

Animal models that elucidate basic principles of the developmental origins of adult diseases

Human epidemiological and animal laboratory studies show that suboptimal environments in the womb and during early neonatal life alter development and predispose the individual to lifelong health problems. The concept of the developmental origins of adult diseases has become well accepted because of the compelling animal studies that have precisely defined the outcomes of specific exposures such as nutrient restriction, overfeeding during pregnancy, maternal stress, and exogenously administered glucocorticoids. This review focuses on the use of animal models to evaluate exposures, mechanisms, and outcomes involved in developmental programming of hypertension, diabetes, obesity, and altered pituitary-adrenal function in offspring in later life. Ten principles of developmental programming are described as fundamental, regardless of the exposure during development and the physiological system involved in the altered outcome. The 10 principles are discussed in the context of the physiological systems involved and the animal model studies that have been conducted to evaluate exposures, mechanisms, and outcomes. For example, the fetus responds to challenges such as hypoxia and nutrient restriction in ways that help to ensure its survival, but this "developmental plasticity" may have long-term consequences that may not be beneficial in adult life. To understand developmental programming, which represents the interaction of nature and nurture, it is necessary to integrate whole animal systems physiology, in vitro cellular biology, and genomic and proteomic approaches, and to use animal models that are carefully characterized and appropriate for the questions under study. Animal models play an important role in this evaluation because they permit combined in vivo and in vitro study at different critical time windows during the exposure and the ensuing developmental responses.     

An historical overview of the activities in the field of exposure and risk assessment of non-ionizing radiation in Bulgaria

Abstract

The exposure and risk evaluation process in Bulgaria concerning non-ionizing radiation health and safety started in the early 1970s. Then, the first research laboratory “Electromagnetic fields in the working environment” was founded in the framework of the Centre of Hygiene, belonging to the Medical Academy, Sofia. The main activities were connected with developing legislation, new equipment for measurement of electromagnetic fields, new methods for measurement and exposure assessment, in vivo and human studies for developing methods, studying the effect of non-ionizing radiation on human body, developing exposure limits. Most of the occupations as metal industry, plastic welding, energetics, physiotherapy, broadcasting, telephone stations, computer industry, etc., have been covered by epidemiological investigations and risk evaluation. In 1986, the ANSI standard for safe use of lasers has been implemented as national legislation that gave the start for studies in the field of risk assessment concerning the use of lasers in industry and medicine. The environmental exposure studies started in 1991 following the very fast implementation of the telecommunication technologies. Now, funds for research are very insignificant, and studies in the field of risk assessment are very few. Nevertheless, Bulgaria has been an active member of the WHO International EMF Project, since 1997, and that gives good opportunity for collaboration with other Member states, and for implementation of new approach in the EMF policy for workers and people’s protection against non-ionizing radiation exposure.     

Detection and disinfection of pathogens in storm-generated flows.

The disease-producing potential of recreational waters is currently estimated through the use of certain bacterial indicators that are believed to be positively correlated with the presence of fecal contamination. In general, these indicators and their recommended limiting values have been adopted for use from existing standard methods for the analysis of sanitary waste water. However, no indicator currently in use today exists solely in the feces of man and not also elsewhere, e.g., in soils, vegetation, and the feces of animals. Storm-water runoff is often rich in bacteria originating from these nonhuman sources and can contain high densities of indicator bacteria; however, existing epidemiological studies of recreational waters receiving storm-water runoff have reported little correlation between current indicator densities and the incidences of swimming illnesses. In addition, microbial analyses of storm-water runoff have revealed a predominance of nonenteric disease-causing bacteria and viruses that have been linked to respiratory illnesses and skin infections. Fecal-based indicators in use today provide no information on the risks resulting from body contact with these nonenteric pathogens. Consequently, for receiving waters containing discharges that originate primarily from separate storm drainage systems, current bacterial indicators are ill suited to accurately assess the water's total illness-producing capabilities. This paper briefly reviews the development of current bacterial standards and evaluates their adoption in the field of storm-water testing. The unique disinfection requirements of storm-generated runoff are discussed, and advanced disinfection practices are reviewed. The need for additional epidemiological studies that address the disease-causing potential of nonhuman and nonenteric pathogens commonly found in storm-water runoff from urban, agricultural, and rural watershed areas is emphasized in order to determine the actual health risks associated with storm water runoff contact.     

Murine mutants in the study of systemic iron metabolism and its disorders: an update on recent advances

Many past and recent advances in the field of iron metabolism have relied upon the use of mouse models of disease. These models have arisen spontaneously in breeder colonies or have been engineered for global or conditional ablation or overexpression of select genes. Full phenotypic characterization of these models typically involves maintenance on iron-loaded or -deficient diets, treatment with oxidative or hemolytic agents, breeding to other mutant lines or other stresses. In this review, we focus on systemic iron biology and the contributions that mouse model-based studies have made to the field. We have divided the field into three broad areas of research: dietary iron absorption, regulation of hepcidin expression and cellular iron metabolism. For each area, we begin with an overview of the current understanding of key molecular and cellular determinants then discuss recent advances. Finally, we conclude with brief comments on prospects for future study. This article is part of a Special Issue entitled: Cell Biology of Metals.     

Nearly right or precisely wrong? Natural versus laboratory studies of vector-borne diseases

Recent studies that compare experimental vector-borne disease systems incorporating elements of natural pathogen-vector-host interactions with model systems using unnatural associations have highlighted quantitative, and even qualitative, differences in the results. Here, Sarah Randolph and Pat Nuttall argue that the use of mathematical models to explore epidemiological processes and patterns depends on accurate parameter values obtained from natural systems.     

Verification, validation and sensitivity studies in computational biomechanics

Computational techniques and software for the analysis of problems in mechanics have naturally moved from their origins in the traditional engineering disciplines to the study of cell, tissue and organ biomechanics. Increasingly complex models have been developed to describe and predict the mechanical behavior of such biological systems. While the availability of advanced computational tools has led to exciting research advances in the field, the utility of these models is often the subject of criticism due to inadequate model verification and validation (V&V). The objective of this review is to present the concepts of verification, validation and sensitivity studies with regard to the construction, analysis and interpretation of models in computational biomechanics. Specific examples from the field are discussed. It is hoped that this review will serve as a guide to the use of V&V principles in the field of computational biomechanics, thereby improving the peer acceptance of studies that use computational modeling techniques.     

Reinfection, exposure and immunity in human schistosomiasis

In this review Paul Hagan will focus on the results of the reinfection studies that have been completed on Schistosoma mansoni in Kenya and Brazil and on S. haematobium in The Gambia. The review will also draw on the data from other immunological, molecular and epidemiological studies that have provided information that may be relevant to an understanding of immunity in human schistosomiasis. No attempt will be made to describe the latest advances that have been reported from studies of the animal models of schistosomiasis; these are adequately dealt with elsewhere.     

Neuroinflammation and oxidative stress: Co-conspirators in the pathology of Parkinson’s disease

Parkinson’s disease (PD) is a complex disease, with genetics and environment contributing to the disease onset. Recent studies of causative PD genes have confirmed the involvement of cellular mechanisms engaged in mitochondrial and UPS dysfunction, oxidative stress and apoptosis in the progressive degeneration of the dopaminergic neurons in PD. In addition, clinical, epidemiological and experimental evidence has implicated neuroinflammation in the disease progression. This review will discuss neuroinflammation in PD, with particular focus on the genetic and toxin-based models of the disease. These studies have confirmed elevated oxidative stress and the pro-inflammatory response occurs early in the disease and these processes contribute to and/or exacerbate the nigro-striatal degeneration. In addition, the experimental models discussed here have also provided strong evidence that these pathways are an important link between the familial and sporadic causes of PD. The potential application of anti-inflammatory interventions in limiting the dopaminergic neuronal cell death in these models is discussed with evidence suggesting that the further investigation of their use as part of multi-targeted clinical trials is warranted.     

Decreased overall virulence in coinfected hosts leads to the persistence of virulent parasites

Multiple infections are known to affect virulence evolution. Some studies even show that coinfections may decrease the overall virulence (the disease-induced mortality of a coinfected host). Yet, epidemiological studies tend to overlook the overall virulence, and within-host models tend to ignore epidemiological processes. Here, I develop an epidemiological model where overall virulence is an explicit function of the virulence of the coinfecting strains. I show that in most cases, a unique strain is evolutionarily stable (in accordance with the model I use here). However, when the overall virulence is lower than the virulence of each of the coinfecting strains (i.e., when coinfections decrease virulence), the evolutionary equilibrium may be invaded by highly virulent strains, leading to the coexistence of two strains on an evolutionary timescale. This model has theoretical and experimental implications: it underlines the importance of overall virulence and of epidemiological feedbacks on virulence evolution.     

ELF magnetic fields: animal studies, mechanisms of action

Animal studies can contribute to addressing the issue of possible greater health risk for children exposed to 50–60 Hz extremely low frequency (ELF) magnetic fields (MFs), mostly in terms of teratological effects and cancer.Teratology has been extensively studied in animals exposed to ELF MFs but experiments have not established adverse developmental effects.Childhood leukaemia has been the only cancer consistently reported in epidemiological studies as associated with exposure to ELF MFs. This association has been the basis for the classification as “possibly carcinogenic to humans” by the International Agency for Research on Cancer in 2002. Animal experiments have provided only limited support for these epidemiological findings. However, none but one study used an animal model for acute lymphoblastic leukaemia (ALL), the main form of childhood leukaemia, and exposures to ELF MFs were not carried out over the whole pregnancy period, when the first hit of ALL is assumed to occur.Moreover, there are no generally accepted biophysical mechanisms that could explain carcinogenic effects of low-level MFs. The radical pair mechanism and related cryptochromes (CRY) molecules have recently been identified in birds and other non-mammalian species, as a sensor of the geomagnetic field, involved in navigation. The hypothesis has to be tested in mammalian models. CRY, which is part of the molecular circadian clock machinery, is a ubiquitous protein likely to be involved in cancer cell growth and DNA repair.In summary, we now have some clues to test for a better characterization of the interaction between ALL and ELF MFs exposure.     

Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy—an approach to a dose assessment

Epidemiological studies related to radiofrequency (RF) electromagnetic fields (EMF) have mainly used crude proxies for exposure, such as job titles, distance to, or use of different equipment emitting RF EMF. The Royal Norwegian Navy (RNoN) has measured RF field emitted from high‐frequency antennas and radars on several spots where the crew would most likely be located aboard fast patrol boats (FPB). These boats are small, with short distance between the crew and the equipment emitting RF field. We have described the measured RF exposure aboard FPB and suggested different methods for calculations of total exposure and annual dose. Linear and spatial average in addition to percentage of ICNIRP and squared deviation of ICNIRP has been used. The methods will form the basis of a job exposure matrix where relative differences in exposure between groups of crew members can be used in further epidemiological studies of reproductive health. Bioelectromagnetics 31:350–360, 2010. © 2010 Wiley‐Liss, Inc.