Temporal and spatial scales in epidemiological concepts.

Traditional concepts in epidemiology are reviewed from ecological, cultural, and logical perspectives. In zoological epidemiology (including the study of human and livestock diseases caused by pathogens), temporal and spatial scales are typically not used in definitions, by hypotheses, and theories concerning epidemic and endemic diseases. The same is true for botanical and theoretical epidemiology, although these two subdisciplines use a different definition of an epidemic than does zoological epidemiology. If hypotheses are to be tested and implemented, more precise concepts that include general temporal and spatial scales are needed. Criteria proposed here for identifying temporal and spatial scales are based on the need for consistency of observation and ecological validity. Consistency of observation depends upon the relative life cycles of the hosts and pathogens and upon the environmental effects that lead to stable or unstable population structures. Pathogens are classified as absent, sporadic, or persistent (endemic). Epidemics can occur in the latter two cases but require a separate evaluation. A definition of an epidemic based on temporal and spatial scales and statistics is proposed for use by all subdisciplines. An epidemic occurs when an indicator variable reaches a statistically unusually high value due to transmission of a pathogen in an ecologically proper space-time unit. Threshold theorems in botanical and theoretical epidemiology are also discussed. These proposals do not directly affect modeling, but changes to hypotheses may influence model analyses.     

Human dimensions indicators of coastal ecosystem services: A hierarchical perspective

Coastal resource management revolves around defining the dynamic between people and the marine and coastal resources they use and depend upon for a large range of goods and services. The process of defining that dynamic is iterative and must account not only for changing natural resource conditions but also for changing social conditions. Decision-making therefore happens within a context of a social system that includes differing levels of capacity, commitment, economics, political mandates and pressures, and cultural and traditional frameworks. The aim of this paper is to introduce a hierarchical approach in which the large number of variables needed to measure the complex, numerous and abstract social concepts used to evaluate the delivery of ecosystem services can be aggregated into smaller sets of indicators, which can ultimately be aggregated into a single report card. These variables and indicators can identify and describe non-economic human dimensions societal benefits derived as ecosystem services that are readily collected, that can identify changes over time, and are appropriate to specific coastal regions. The identified indicators would capture changes in the delivery of overall ecosystem services impacted by, or that will impact, changes in particular sets of environmental characteristics that are valued by society at large.     

Shared Cultural History as a Predictor of Political and Economic Changes among Nation States

Political and economic risks arise from social phenomena that spread within and across countries. Regime changes, protest movements, and stock market and default shocks can have ramifications across the globe. Quantitative models have made great strides at predicting these events in recent decades but incorporate few explicitly measured cultural variables. However, in recent years cultural evolutionary theory has emerged as a major paradigm to understand the inheritance and diffusion of human cultural variation. Here, we combine these two strands of research by proposing that measures of socio-linguistic affiliation derived from language phylogenies track variation in cultural norms that influence how political and economic changes diffuse across the globe. First, we show that changes over time in a country’s democratic or autocratic character correlate with simultaneous changes among their socio-linguistic affiliations more than with changes of spatially proximate countries. Second, we find that models of changes in sovereign default status favor including socio-linguistic affiliations in addition to spatial data. These findings suggest that better measurement of cultural networks could be profoundly useful to policy makers who wish to diversify commercial, social, and other forms of investment across political and economic risks on an international scale.     

Variability of 3D arterial geometry and dynamics,and its pathologic implications

Geometric parameters and features vary within the vasculature. Furthermore, at any given anatomic site, there are substantial variations in geometry among individuals. These variations can contribute to a corresponding variability in the hemodynamic environment and, to the extent that hemodynamics affects the atherosclerotic process, the progress of vascular disease. Measurements of the geometry and wall morphometry of post-mortem human coronary arteries demonstrate a relationship between these variables that supports the notion that geometric variations can contribute to a corresponding variability in the local rate of progression of arterial disease. The dynamic geometry of the coronary arteries also varies from site to site and among individuals, and this variability too may play a role in the epidemiology of coronary artery disease.     

The systematics and population genetics of Opisthorchis viverrini sensu lato: implications in parasite epidemiology and bile duct cancer

Together with host and environmental factors, the systematics and population genetic variation of Opisthorchis viverrini may contribute to recorded local and regional differences in epidemiology and host morbidity in opisthorchiasis and cholangiocarcinoma (CCA). In this review, we address recent findings that O. viverrini comprises a species complex with varying degrees of population genetic variation which are associated with specific river wetland systems within Thailand as well as the Lao PDR. Having an accurate understanding of systematics is a prerequisite for a meaningful assessment of the population structure of each species within the O. viverrini complex in nature, as well as a better understanding of the magnitude of genetic variation that occurs within different species of hosts in its life cycle. Whether specific genotypes are related to habitat type(s) and/or specific intermediate host species are discussed based on current available data. Most importantly, we focus on whether there is a correlation between incidence of CCA and genotype(s) of O. viverrini. This will provide a solid basis for further comprehensive investigations of the role of genetic variation within each species of O. viverrini sensu lato in human epidemiology and genotype related morbidity as well as co-evolution of parasites with primary and secondary intermediate species of host.     

Emerging helminth zoonoses

As our ability to recognise and diagnose human disease caused by helminth parasites has improved, so our understanding of the epidemiology and clinical manifestations of these diseases has improved. Humans can develop patent infection with a wide range of helminth parasites, whose natural host is another vertebrate. Rather than focusing on a comprehensive review of zoonotic helminth infections, this review describes in detail examples of zoonotic helminth infections that have newly appeared in human populations, or have existed but are increasing in incidence or geographic range. Examples include intestinal capillariasis, anisakidosis, eosinophilic enteritis, oesophagostomiasis and gnathostomiasis. Potential reasons for the emergence of these infections, including changes in social, dietary or cultural mores, environmental changes, and the improved recognition of heretofore neglected infections often coupled with an improved ability to diagnose infection are discussed.     

Spatial and temporal modelling for parasite transmission studies and risk assessment

Spatial and temporal modelling of parasite transmission and risk assessment require relevant spatial information at appropriate spatial and temporal scales. There is now a large literature that demonstrates the utility of satellite remote sensing and spatial modelling within geographical information systems (GIS) and firmly establishes these technologies as the key tools for spatial epidemiology. This review outlines the strength of satellite remotely sensed data for spatial mapping of landscape characteristics in relation to disease reservoirs, host distributions and human disease. It is suggested that current satellite technology can fulfill the spatial mapping needs of disease transmission and risk modelling, but that temporal resolution, which is a function of the satellite data acquisition characteristics, may be a limitating factor for applications requiring information about landscape or ecosystem dynamics. The potential of the Modis sensor for spatial epidemiology is illustrated with reference to mapping spatial and temporal vegetation dynamics and small mammal parasite hosts on the Tibetan plateau. Future research directions and priorities for landscape epidemiology are considered.     

Spatial scale and evolutionary history determine the degree of taxonomic homogenization across island bird assemblages

It is widely documented that human activities have elevated the extirpation of natural populations as well as the successful introduction to new areas of non-native species. These dual processes of introduction and extirpation can change the similarity of communities, but the direction and magnitude these changes take are likely to depend on the manner in which introductions and extirpations occur, the spatial scale at which the changes are measured, and the initial similarity of the communities before the human-induced drivers occurred. Here, we explore patterns of extirpation and introduction and their influence on the similarity of global oceanic island bird assemblages from four different Oceans (Atlantic, Caribbean, Indian, Pacific). We show that different historical patterns of introduction and extirpation have produced varying trends in compositional similarity both between islands within archipelagos and between islands across different archipelagos within the same ocean. Patterns of bird assemblage convergence (i.e. taxonomic homogenization) or divergence (i.e. taxonomic differentiation) among islands depended on the scale of examination, the evolutionary associations among species of the region, and the cultural history of human colonization. These factors are all likely to be leading to a series of multiple interacting processes that are shaping the complex compositional changes observed among global island bird faunas over time.     

A multilevel analytical framework for studying cultural evolution in prehistoric hunter–gatherer societies

Over the past decade, a major debate has taken place on the underpinnings of cultural changes in human societies. A growing array of evidence in behavioural and evolutionary biology has revealed that social connectivity among populations and within them affects, and is affected by, culture. Yet the interplay between prehistoric hunter–gatherer social structure and cultural transmission has typically been overlooked. Interestingly, the archaeological record contains large data sets, allowing us to track cultural changes over thousands of years: they thus offer a unique opportunity to shed light on long‐term cultural transmission processes. In this review, we demonstrate how well‐developed methods for social structure analysis can increase our understanding of the selective pressures underlying cumulative culture. We propose a multilevel analytical framework that considers finer aspects of the complex social structure in which regional groups of prehistoric hunter–gatherers were embedded. We put forward predictions of cultural transmission based on local‐ and global‐level network metrics of small‐scale societies and their potential effects on cumulative culture. By bridging the gaps between network science, palaeodemography and cultural evolution, we draw attention to the use of the archaeological record to depict patterns of social interactions and transmission variability. We argue that this new framework will contribute to improving our understanding of social interaction patterns, as well as the contexts in which cultural changes occur. Ultimately, this may provide insights into the evolution of human behaviour.     

Burkholderia cepacia complex species: health hazards and biotechnological potential

The Burkholderia cepacia complex is a group of nine closely related bacterial species that have useful properties in the natural environment as plant pest antagonists, plant growth promoters and degradative agents of toxic substances. Because these species are human opportunistic pathogens, especially in cystic fibrosis patients, biotechnological applications that involve environmental releases have been severely restricted. Recent progress in understanding the taxonomy, epidemiology and ecology of the B. cepacia complex species has unravelled considerable variability in their pathogenicity and ecological properties, which has set the basis for a reassessment of the risk posed by individual species to human health.     

Changing cultures, changing cuisines: Cultural transitions and dietary change in Iron Age, Roman, and Early Medieval Croatia

Food is well-known to encode social and cultural values, for example different social groups use different consumption patterns to act as social boundaries. When societies and cultures change, whether through drift, through population replacement or other factors, diet may also alter despite unchanging resource availability within a region. This study investigates the extent to which dietary change coincides with cultural change, to understand the effects of large-scale migrations on the populations' diets. Through stable carbon and nitrogen isotope analysis of Iron Age, Roman, and Early Medieval human bone collagen, we show that in Croatia large-scale cultural change led to significant changes in diet. The isotopic evidence indicates that Iron Age diet consisted of C(3) foodstuffs with no isotopic evidence for the consumption of C(4) or marine resources. With the Roman conquest, marine resources were added to the diet, although C(3) foodstuffs continued to play an important role. In the Early Medieval period, this marine component was lost and varying amounts of C(4) foodstuffs, probably millet, were added to the otherwise C(3) diet. In both of these transitions it is likely that the changes in diet are related to the arrival of a new people into the area.     

The evolution of epidemic influenza

Recent developments in complete-genome sequencing, antigenic mapping and epidemiological modelling are greatly improving our knowledge of the evolution of human influenza virus at the epidemiological scale. In particular, recent studies have revealed a more complex relationship between antigenic evolution, natural selection and reassortment than previously realized. Despite these advances, there is much that remains to be understood about the epidemiology of influenza virus, particularly the processes that determine the virus's strong seasonality. We argue that a complete understanding of the evolutionary biology of this important human pathogen will require a genomic view of genetic diversity, including the acquisition of polymorphism data from within individual hosts and from geographical regions, particularly the tropics, which have been poorly surveyed to date.     

Effects of natural selection on interpopulation divergence at polymorphic sites in human protein-coding Loci

To develop new strategies for searching for genetic associations with complex human diseases, we analyzed 2784 single-nucleotide polymorphisms (SNPs) in 396 protein-coding genes involved in biological processes relevant to cancer and other complex diseases, with respect to gene diversity within samples of individuals representing the three major historic human populations (African, European, and Asian) and with respect to interpopulation genetic distance. Reduced levels of both intrapopulation gene diversity and interpopulation genetic distance were seen in the case of SNPs located within the 5'-UTR and at nonsynonymous SNPs, causing radical changes to protein structure. Reduction of gene diversity at SNP loci in these categories was evidence of purifying selection acting at these sites, which in turn causes a reduction in interpopulation divergence. By contrast, a small number of SNP sites in these categories revealed unusually high genetic distances between the two most diverged populations (African and Asian); these loci may have historically been subject to divergent selection pressures.     

Plausible mechanisms for brain structural and size changes in human evolution

Encephalization has many contexts and implications. On one hand, it is concerned with the transformation of eating habits, social relationships and communication, cognitive skills and the mind. Along with the increase in brain size on the other hand, encephalization is connected with the creation of more complex brain structures, namely in the cerebral cortex. It is imperative to inquire into the mechanisms which are linked with brain growth and to find out which of these mechanisms allow it and determine it. There exist a number of theories for understanding human brain evolution which originate from neurological sciences. These theories are the concept of radial units, minicolumns, mirror neurons, and neurocognitive networks. Over the course of evolution, it is evident that a whole range of changes have taken place in regards to heredity. These changes include new mutations of genes in the microcephalin complex, gene duplications, gene co-expression, and genomic imprinting. This complex study of the growth and reorganization of the brain and the functioning of hereditary factors and their external influences creates an opportunity to consider the implications of cultural evolution and cognitive faculties.     

Cultural Rules, Rituals, and Behavior Regulation

While it is generally agreed that culture and biology are both relevant to an understanding of human behavior, there is little consensus about the appropriate use of reductionist procedures. Disagreement abounds concerning the nature of the interaction and the relative contribution of distal and proximal mechanisms. An understanding of such issues may emerge only with long study of the interaction of variables at different conceptual levels of organization that intervene between the genes and culture. It is toward this larger end that the limited efforts of this paper are directed. Two cultural phenomena are considered: Murdoch's "social laws of sexual choice," and aspects of human ritual behavior. Although these constitute a unique organization of cultural items, I attempt to show how they are influenced by underlying biopsychological processes. I specifically reject, however, the view that cultural phenomena are isomorphic with, or can be completely reduced to, such processes. Emergent novelty and multiple possibilities are always present at more inclusive levels of organization. I argue that the relationship between the different sets of system variables is based on homologous functions and not merely on analogies.
SEYMOUR PARKER is Professor, Department of Anthropology, University of Utah, Salt Lake City. UT 84112     

Inter-individual differences in the metabolism of environmental toxicants: cytochrome P450 1A2 as a prototype.

Cytochrome P450 (P450) 1A2 provides an interesting paradigm for inter-individual differences in the metabolism of pro-carcinogens. The enzyme is known to vary 40-fold among individuals and may contribute to cancers caused by heterocyclic amines and other chemicals. Rat and human P450 1A2 are known to be 75% identical and were compared for several catalytic activities. The human enzyme was an order of magnitude more efficient in the N-hydroxylation of two heterocyclic amines. Further, the levels of P450 1A2 expressed in human livers show a 40-fold variation, with some as high as 0.25 nmol P450 1A2 per milligram microsomal protein. Some human liver samples are more active (than those isolated from polychlorinated biphenyl-treated rats) in the activation of heterocyclic amines. A bacterial genotoxicity assay has been developed in which human P450 1A2 and NADPH-P450 reductase are expressed within Escherichia coli and bacterial mutants can be assayed using reversion to lac prototrophy. A random mutagenesis strategy for human P450 1A2 has been developed and used to examine the changes in catalytic activity seen with many single-amino acid substitutions. These results may be of relevance in consideration of genetic polymorphisms. Further, the findings pose a challenge to molecular epidemiology effort in that results with one substrate do not necessarily predict those for others. Some dinitropyrenes are P450 1A2 substrates but others are not. 6-Nitrochrysene can be activated by human P450 1A2 but the (mono) nitropyrenes examined were not; these were oxidized by P450 3A4 instead.     

The epidemiology of malaria in Papua New Guinea

Papua New Guinea (PNG) is a patchwork of different ecological zones, inhabited by human populations of exceptional cultural and linguistic diversity. This results in complex variations in vector ecology and malaria epidemiology. Malaria is the main cause of morbidity in many health facilities in lowland areas, but it is absent in much of the highlands. All four human malaria species occur, but endemicity varies widely, with Plasmodium falciparum locally reaching holo-endemic levels that are rarely found outside sub-Saharan Africa. The high frequency of Plasmodium vivax is an important difference to most African situations. PNG is therefore a prime location for studies of interactions between different parasite species, and of the biology of local human genetic adaptation and its implications for malaria morbidity and mortality.