Control Strategies for the Spread of Malaria in Humans With Variable Attractiveness

The transmission dynamics of malaria in humans with variable attractiveness is modeled with the possibility of prophylactic measures such as personal protection and treatment. At the disease-free equilibria, the basic reproduction number and a measure for effective disease control are computed. Simulations show that a 10% increase in personal protection leads to a decrease in secondary transmission, and that a 10% increase in the treatment rate leads to a 7% reduction in secondary transmission. Personal protection and effective treatment should be applied together. Personal protection fails with increasing degree of attractiveness.     

Models and Proposals for Malaria: A Review

Mathematical models to study the dynamics of malaria continue to be developed and upgraded on the parasite component, which is the causative agent for malaria; on the human component that serves as a reservoir of infection for the blood feeding female mosquitoes; on the disease transmitting vector, the component mostly responsible for the movement of the parasite agent from one human to another; or on the life cycle of the malaria parasite as a pathogen both within the human and vector populations. The consideration of so-far neglected features can be beneficial for the control of malaria.     

The Life Course,Cohort Dynamics,and International Differences in Aging Trajectories

In recent years, population health research has focused on understanding the determinants of later-life health. Two strands of that work have focused on (1) international comparisons of later-life health and (2) assessing the early-life origins of disease and disability and the importance of life course processes. However, the less frequently examined intersection of these approaches remains an important frontier. The present study contributes to the integration of these approaches. We use the Health and Retirement Study family of data sets and a cohort dynamic approach to compare functional health trajectories across 12 high-income countries and to examine the role of life course processes and cohort dynamics in contributing to variation in those trajectories. We find substantial international variation in functional health trajectories and an important role of cohort dynamics in generating that variation, with younger cohorts often less healthy at comparable ages than the older cohorts they are replacing. We further find evidence of heterogeneous effects of life course processes on health trajectories. The results have important implications for future trends in morbidity and mortality as well as public policy.     

Ergodicity and extinction in a stochastic susceptible-infected-recovered-susceptible epidemic model with influence of information

An epidemic model with stochastic contact transmission coefficient takes into account white noise and the influence of information. Sufficient conditions for the extinction and persistence of the disease are expressed. The existence of a stationary distribution and the ergodic property are proved. The peak of infected population can be decreased by information. The analytical results are showed by simulations and the influence of white noise and information on the dynamics of epidemics are evaluated.     

The Depopulation of Hispanic America after the Conquest

During the century following Columbus's landfall, the population of America experienced a precipitous decline. A widely accepted explanation is the diffusion of Eurasian pathogens among the nonimmune Indians with the attendant catastrophic mortality. Contemporary observers—conquerors, administrators, missionaries, and chroniclers—while mentioning disease among factors in the decline, were convinced that the demographic collapse was due to a plurality of factors, such as serfdom and the confiscation of labor, excessive work, economic and social dislocation, wars and conflicts, and impediments to reproduction. Reconsideration of historical evidence supports the notion that new pathologies cannot satisfactorily explain the varying demographic impacts of Conquest. The Tainos of the Antilles were on the verge of extinction before the first smallpox epidemics struck the islands in 1518; the Guaranís of Paraguay were flourishing in spite of recurrent epidemics; in Peru civil wars were the major cause of decline during the first two decades of Spanish rule. A reappraisal of the Indian catastrophe must consider—together with the impact of the new viruses—the modes and circumstances of European domination.     

Stabilization effects of spatial aggregation of vectors in plant disease systems

Stabilization effects of spatial aggregation of vectors were examined in insect-borne plant disease systems by constructing a model that describes the yearly dynamics of rice stripe virus disease transmitted by the small brown planthopperLaodelphax striatellus (Fallén). Two transmission paths between vectors were considered: vertical transmission from parents through eggs, and horizontal transmission from infected plants by acquisition feeding. In this model, a paddy field was divided into quadrats and horizontal transmission was assumed to occur within each quadrat. A negative binomial distribution was used to describe the frequency distribution of vectors per quadrat. The parameters of the model were estimated using field data collected in Ibaraki Prefecture, Japan. The model showed that (1) the disease cannot invade into an epidemiological system if the mean crowding of vectors is less than a critical value, (2) the proportion of infected vectors is maintained at about 30% irrespective of the vector density if vectors are highly aggregated, and (3) the proportion of infected plants is maintained at a low level irrespective of the vector density if vectors are highly aggregated. It was also shown that these stabilization effects of aggregation in this epidemiological system come from a mechanism that is common to other systems such as single-species systems and competition systems.     

Urbanization as a Global Historical Process: Theory and Evidence from sub‐Saharan Africa

Urbanization has traditionally been understood as a byproduct of economic development, but this explanatory framework fails to account for the phenomenon of “urbanization without growth” observed in sub‐Saharan Africa throughout the 1980s and 1990s. In light of this apparent anomaly, I argue that urbanization is better understood as a global historical process driven by population dynamics associated with technological and institutional innovations that have substantially improved disease control and food security in urban settlements across the globe. These innovations first emerged in Europe in the eighteenth and nineteenth centuries and were subsequently diffused through colonialism, trade, and international development assistance. A range of qualitative and quantitative evidence is presented to demonstrate that this historically grounded theory of urbanization offers a more convincing explanation for the stylized facts of Africa's urban transition—and hence the process of world urbanization more broadly—than the traditional economic account.     

Infectious diseases -- new and ancient threats to world health

Infectious and parasitic diseases remain a leading cause of death and disability in developing countries and are re-emerging as a serious health problem in developed countries. Outbreaks of Ebola, dengue hemorrhagic fever, cholera, and bubonic plague have occurred in low-income countries and multidrug-resistant organisms have surfaced throughout the world. Since 1973, over 28 new disease-causing microbes have been identified. This issue of "Population Bulletin" analyzes the impact of factors such as population growth, urbanization, migration, poverty, travel, agricultural practices, climate changes, natural disasters, and medical technology on the resurgence of infectious and parasitic diseases as well as the influence of diseases such as AIDS on population dynamics and socioeconomic development. Most of these diseases could be prevented, cured, or eradicated with known public health measures. National governments can help reduce poverty, step up immunization programs, and lessen the chances of introducing new diseases. Nongovernmental organizations can disseminate preventive knowledge and monitor disease outbreaks. The medical profession can strengthen infection control precautions and institute surveillance of the use of antibiotics and other antimicrobial agents. Since the geographic isolation that used to contain disease outbreaks has been replaced by permeable international borders, the campaign against infectious and parasitic diseases must be global.     

An econometric and neoclassical analysis of the timing and spacing of births in Canada from 1950 to 1990

This paper estimates a reduced form neoclassical model of Canadian fertility dynamics using an econometric technique that integrates several features not usually found in the demographic and economic literature. We find considerable support for the neoclassical model. We also find that correlated unobservables and parity stopping effects play an important role in Canadian fertility dynamics as well as other socio-demographic features of Canadian women. However, we fail to totally characterize the important drops in the fertility rate that took place for this era. Received: 2 May 1996 / Accepted: 27 March 1997     

Seasonal forcing on the dynamics ofClethrionomys rufocanus: Modeling geographic gradients in population dynamics

We interpret gradients in population dynamics of the gray-sided vole from the southwestern part of the island of Hokkaido to its northeastern part within the framework of a phenomenological model involving the relative length of summer and winter. In Hokkaido, as in other northern regions, both spring and fall is considered as short transition periods between the two main seasons — summer (the primary breeding season) and winter (the non-reproductive or secondary breeding season). We show that the geographic transition in dynamics may be understood as the combined consequence of different patterns of density-dependence during summer and winter, and geographically varying season lengths. Differences are shown to exist between summer and winter with respect to strength of density-dependence. Direct density-dependence, in particular, is stronger during winter than during summer. A model is presented to show how relative lengths of seasons can induce both stable and periodically fluctuating population dynamics. The results are compared and contrasted with what is otherwise known about the gradient in rodent dynamics in Fennoscandia.     

The Population Education Transition Curve: Education Gradients Across Population Exposure to New Health Risks

The salutary effect of formal education on health-risk behaviors and mortality is extensively documented: ceteris paribus, greater educational attainment leads to healthier lives and longevity. Even though the epidemiological evidence has strongly indicated formal education as a leading “social vaccine,” there is intermittent reporting of counter-education gradients for health-risk behavior and associated outcomes for certain populations during specific periods. How can education have both beneficial and harmful effects on health, and under which contexts do particular effects emerge? It is useful to conceptualize the influence of education as a process sensitive to the nature, timing of entry, and uniqueness of a new pleasurable and desirable lifestyle and/or product (such as smoking) with initially unclear health risks for populations. Developed herein is a hypothesis that the education gradient comprises multiple potent pathways (material, psychological, cognitive) by which health-risk behaviors are influenced, and that there can be circumstances under which pathways act in opposite directions or are differentially suppressed and enhanced. We propose the population education transition (PET) curve as a unifying functional form to predict shifting education gradients across the onset and course of a population’s exposure to new health risks and their associated consequences. Then, we estimate PET curves for cases with prior epidemiological evidence of heterogeneous education gradients with health-risk behaviors related to mass-produced cigarettes in China and the United States; saturated fats, sugar, and processed food diets in Latin America; and HIV infection in sub-Saharan Africa. Each offers speculation on interactions between environmental factors during population exposure and education pathways to health-risk behaviors that could be responsible for the temporal dynamics of PET curves. Past epidemiological studies reporting either negative or positive education gradients may not represent contradictory findings as much as come from analyses unintentionally limited to just one part of the PET process. Last, the PET curve formulation offers richer nuances about educational pathways, macro-historical population dynamics, and the fundamental cause of disease paradigm.     

人口变动对气候变化的影响

人口与气候变化关系是一个非常缺乏研究的领域。本文总结近年有关人口变动对气候变化影响研究领域的状况,讨论不同研究方法和模型的应用成果及其局限性,特别介绍了应用整合评估模型iPETS对主要国家和地区温室气体排放预测结果,指出人口变动与经济发展、技术变动等都是人类影响气候变化的决定因素;人口变动的影响不只是人口规模的增减,人口和家庭户结构及其空间分布的变化也是应该考虑的内容;家庭户应该成为气候变化研究的人口分析单位;人口老化、城市化、家庭规模缩小等都是影响未来气候变化的重要人口因素。本研究提供了改进气候预测模型对人口变量处理方式的实例,指出了在制定减缓气候变化政策过程中考虑人口因素的重要性和可操作建议。     

An individual-based model for competingDrosophila populations

An individual-based model forDrosophila is formulated, based on competition amongst larvae consuming the same batch of food. The predictions of the model are supported by data for single speciesDrosophila populations reared in the laboratory. The model is used to build a simple discrete model for the dynamics ofDrosophila populations that are kept over a number of generations. The dynamics of a single species is shown to give either a stable equilibrium or fluctuations which can be periodic or chaotic. When the dynamics of a species in the absence of the other is periodic or chaotic, we found coexistence or two alternative states, on neither of which the species can coexist.     

人口对干旱区生态环境演变的作用机制与问题分析——以新疆为例

本文以中国最大的干旱区———新疆为例 ,分析了干旱区人口变动与生态环境退化之间的主要作用机制以及存在的主要矛盾。认为人口数量增长引起的资源环境压力 ,是导致干旱区环境退化的主要人为诱因 ,而人口的素质状况则决定了人口资源环境压力下最终的环境演化方向与后果。在各种矛盾中 ,人口的快速增长所导致的资源环境压力 ,是目前新疆人口与环境之间最大的矛盾 ,而不均匀的人口空间分布模式则加剧了这种资源环境压力 ,新疆较低的人口综合素质则决定了新疆长期以来在资源环境面前所采取的主要方式和最终环境后果 ,是以环境退化为主的表现模式。     

Young Adult Dating Relationships and the Management of Sexual Risk

Young adult involvement in sexual behavior typically occurs within a relationship context, but we know little about the ways in which specific features of romantic relationships influence sexual decision-making. Prior work on sexual risk taking focuses attention on health issues rather than relationship dynamics. We draw on data from the Toledo Adolescent Relationships Study (n = 475) to examine the association between qualities and dynamics of current/most recent romantic relationships such as communication and emotional processes, conflict, demographic asymmetries, and duration and the management of sexual risk. We conceptualize ‘risk management’ as encompassing multiple domains, including (1) questioning the partner about previous sexual behaviors/risks, (2) using condoms consistently, and (3) maintaining sexual exclusivity within the relationship. We identify distinct patterns of risk management among dating young adults and find that specific qualities and dynamics of these relationships are linked to variations in risk management. Results from this paper suggest the need to consider relational dynamics in efforts to target and influence young adult sexual risk-taking and reduce STIs, including HIV.     

Analyzing migration decisions: the first step-whose decisions?

Many theories of geographic mobility assume that the change-of-residence process includes a substantial degree of choice. This paper classifies stated reasons for moving from the 1973 through 1977 Annual Housing Survey into forced, imposed, and preference-dominated categories. About 25 percent of residential mobility and 40 percent of migration occurred under conditions of substantial constraint. Mobility was most often constrained by family dynamics; for migration, occupational relocations frequently imposed the decision-to-move process and determined destinations. The volume of constrained movement indicates that its impact upon individuals, population dynamics, and voluntaristic theories of mobility deserves greater consideration.     

Up and on or down and out? Gender, immigration and the consequences of temporary employment in Canada

What happens to temporary workers when their jobs end? Is temporary employment a fleeting way station to a better job, or does it herald an ongoing cycle of precariousness? What are the implications of temporary employment dynamics for broader patterns of inequality in labour markets? European researchers have focused increasing attention on these issues in the context of concern about the relationship between inequality and insecurity in labour markets with strong regulatory protections for insiders. However, research on the outcomes of temporary employment in the less regulated labour markets of North America remains limited. This paper draws on rich representative panel data from Statistics Canada's Survey of Labour and Income Dynamics (SLID) and competing risks Cox regression to assess the outcomes and dynamics of temporary employment in this understudied context. Key contributions include more precise estimates of transitions, consideration of multiple theoretically relevant outcomes (permanent jobs; new temporary jobs; and periods of unemployment and labour force withdrawal), and situation of the effect of gender and immigration status on temporary employment transitions in the context of the dynamics of permanent jobs. Findings present a more pessimistic picture of overall temporary job outcomes than prior research but suggest that the dynamics of temporary work do not magnify inequalities of gender and immigration status.     

How do Recent Population Trends Matter to Climate Change?

Although integrated assessment models (IAM) of the Intergovernmental Panel on Climate Change (IPCC) consider population as one of the root causes of greenhouse gas emissions, how population dynamics affect climate change is still under debate. Population is rarely mentioned in policy debates on climate change. Studies in the past decade have added significantly to understanding the mechanisms and complexity of population and climate interactions. In addition to the growth of total population size, research shows that changes in population composition (i.e. age, urban–rural residence, and household structure) generate substantial effects on the climate system. Moreover, studies by the impact, vulnerability and adaptation (IAV) community also reveal that population dynamics are critical in the near term for building climate change resilience and within adaptation strategies. This paper explores how global population dynamics affect carbon emissions and climate systems, how recent demographic trends matter to worldwide efforts to adapt to climate change, and how population policies could make differences for climate change mitigation and adaptation.     

Mass immigration and population dynamics in israel

Israel, in her 25 years of existence, received an unprecedented volume of immigration, which was the major source of her high population growth. This immigration was heavily concentrated in the first five years, 1948-1952; mass immigration of 711,000 supplemented an initial population of 630;000. Subsequently, since 1952, a very peculiar age-sex structure has developed: namely, instead of a pyramid, a wide rectangle for the younger age groups "topped" with a narrow pyramid for the older age groups. The peculiar age-sex dynamics is analyzed in relation to the volume of immigration with its uneven time distribution, the age selectivity of migrants and fertility-mortality patterns of migrants. It is concluded that the uneven time distribution of immigration and the higher fertility of migrants are jointly responsible for the development of Israel's peculiar age dynamics, and that the absence of either of these two factors alone would eliminate it. The peculiar dynamics has societal implications in the short and the long run, some of which are discussed.     

The colonialism of Canada’s Métis health population dynamics: caught between bad data and no data at all

In the last two decades, Canada’s brand of colonial recognition politics has fueled several social and cultural changes that have, in turn, produced startling growths in the “Métis population” in Canada. Demographers and policy makers alike have expressed dubiousness about the extent to which “non-demographic factors” (that is, factors other than fertility and mortality) are fueling this growth, a dubiousness expressed in the growing use of “ethnic mobility” to explain population growth. In this article I explore the historical contexts within which the idea of a single Métis population took hold as a statistical technology, the kinds of social and cultural juxtaposition that making use of a single population masks, and the impact single population estimates have on the ability of Métis nation policy actors to fashion evidence-based policy relevant to the concerns of the Métis nation. While the dynamics and the data perused in this article are specific to Canada, they possess broader resonances with other nation-states grappling with their colonial histories and longstanding Indigenous peoples as these dynamics relate to official data dynamics.