Global warming is changing the dynamics of Arctic host-parasite systems

Global climate change is altering the ecology of infectious agents and driving the emergence of disease in people, domestic animals, and wildlife. We present a novel, empirically based, predictive model for the impact of climate warming on development rates and availability of an important parasitic nematode of muskoxen in the Canadian Arctic, a region that is particularly vulnerable to climate change. Using this model, we show that warming in the Arctic may have already radically altered the transmission dynamics of this parasite, escalating infection pressure for muskoxen, and that this trend is expected to continue. This work establishes a foundation for understanding responses to climate change of other host-parasite systems, in the Arctic and globally.

Mapping the basic reproduction number (R₀) for vector-borne diseases: a case study on bluetongue virus

Geographical maps indicating the value of the basic reproduction number, R₀, can be used to identify areas of higher risk for an outbreak after an introduction. We develop a methodology to create R₀ maps for vector-borne diseases, using bluetongue virus as a case study. This method provides a tool for gauging the extent of environmental effects on disease emergence. The method involves integrating vector-abundance data with statistical approaches to predict abundance from satellite imagery and with the biologically mechanistic modelling that underlies R₀. We illustrate the method with three applications for bluetongue virus in the Netherlands: 1) a simple R₀ map for the situation in September 2006, 2) species-specific R₀ maps based on satellite-data derived predictions, and 3) monthly R₀ maps throughout the year. These applications ought to be considered as a proof-of-principle and illustrations of the methods described, rather than as ready-to-use risk maps. Altogether, this is a first step towards an integrative method to predict risk of establishment of diseases based on mathematical modelling combined with a geographic information system that may comprise climatic variables, landscape features, land use, and other relevant factors determining the risk of establishment for bluetongue as well as of other emerging vector-borne diseases.

Canine leishmaniasis in southeastern Spain

To examine prevalence changes and risk factors for canine leishmaniasis, we conducted a cross-sectional seroprevalence study and a survey during April–June 2006. Seroprevalence had increased at the meso-Mediterranean bioclimatic level over 22 years. Risk was highest for dogs that were older, large, lived outside, and lived at the meso-Mediterranean level.

The evolution of water balance in Glossina (Diptera: Glossinidae): correlations with climate

The water balance of tsetse flies (Diptera: Glossinidae) has significant implications for understanding biogeography and climate change responses in these African disease vectors. Although moisture is important for tsetse population dynamics, evolutionary responses of Glossina water balance to climate have been relatively poorly explored and earlier studies may have been confounded by several factors. Here, using a physiological and GIS climate database, we investigate potential interspecific relationships between traits of water balance and climate. We do so in conventional and phylogenetically independent approaches for both adults and pupae. Results showed that water loss rates (WLR) were significantly positively related to precipitation in pupae even after phylogenetic adjustment. Adults showed no physiology-climate correlations. Ancestral trait reconstruction suggests that a reduction in WLR and increased size probably evolved from an intermediate ancestral state and may have facilitated survival in xeric environments. The results of this study therefore suggest an important role for water balance physiology of pupae in determining interspecific variation and lend support to conclusions reached by early studies of tsetse physiology.

Global warming and malaria: knowing the horse before hitching the cart

Speculations on the potential impact of climate change on human health frequently focus on malaria. Predictions are common that in the coming decades, tens - even hundreds - of millions more cases will occur in regions where the disease is already present, and that transmission will extend to higher latitudes and altitudes. Such predictions, sometimes supported by simple models, are persuasive because they are intuitive, but they sidestep factors that are key to the transmission and epidemiology of the disease: the ecology and behaviour of both humans and vectors, and the immunity of the human population. A holistic view of the natural history of the disease, in the context of these factors and in the precise setting where it is transmitted, is the only valid starting point for assessing the likely significance of future changes in climate.

Epidemiology of West Nile infection in Volgograd, Russia, in relation to climate change and mosquito (Diptera: Culicidae) bionomics

In 1999, there was the large outbreak of West Nile fever (WNF) in Southern Russia (>500 cases in the Volgograd Province). In 2000-2004, the WNF incidence rate decreased steadily to zero, but a new outbreak occurred in 2007 (64 cases). The analysis of historical climate data for Volgograd from 1900 to present showed that the years 1999 and 2007 were the hottest ones due to a very mild "winter" (Dec.-Mar.) and a hot "summer" (June-Sep.). There are up to 15 potential WNF vectors in Volgograd, but only Culex pipiens and Culex modestus are abundant in late summer, both in urban and rural settings. Only these species are naturally attracted to and feed on both humans and birds. The RNA of pathogenic WN virus genovariant was found by reverse transcriptase polymerase chain reaction only in Culex mosquitoes at the infection rate of about 0.04%. So these species may be considered as potential WNF "bridge vectors" between birds and humans as well as main vectors in sylvatic avain cycle. Their abundance in an epidemic season was higher in the years with a mild winter and a hot summer, so this phenomenon may serve as a connecting link between a climate and WNF epidemiology. These findings give some hints on the predisposing factors for WNF epidemic as well as the possibility to predict WNF outbreaks in the temperate climate zones.

Climate change effects on plague and tularemia in the United States

Plague and tularemia are serious zoonotic diseases endemic to North America. We evaluated spatial patterns in their transmission in view of changing climates. First, we tested whether observed shifts since the 1960s are consistent with expected patterns of shift given known climate changes over that period. Then, we used general circulation model results summarizing global patterns of changing climates into the future to forecast likely shifts in patterns of transmission over the next 50 years. The results indicate that these diseases are indeed shifting in accord with patterns of climatic shift, but that overall geographic shifts will likely be subtle, with some northward movement of southern limits and possibly northward movement of northern limits as well.

Preparing the U.S. health community for climate change

In society's effort to address and prepare for climate change, the health community itself must ensure that it is prepared. Health personnel will require flexible and iterative action plans to address climate change at the individual, hospital, local health department, state, and national levels. This requires that health workers analyze the impact of climate change with a view to human health, and then formulate robust policy and demonstrate authentic leadership. In this review, we summarize the status of the health community's preparation for climate change and provide specific recommendations for action at each level. Although preparation status and recommendations vary, our observation is that it is not enough for public health and medical care agencies and departments to develop policies and advocate change. They have a direct responsibility to demonstrate substantive leadership.

Health impact assessment of global climate change: expanding on comparative risk assessment approaches for policy making

Climate change is projected to have adverse impacts on public health. Cobenefits may be possible from more upstream mitigation of greenhouse gases causing climate change. To help measure such cobenefits alongside averted disease-specific risks, a health impact assessment (HIA) framework can more comprehensively serve as a decision support tool. HIA also considers health equity, clearly part of the climate change problem. New choices for energy must be made carefully considering such effects as additional pressure on the world's forests through large-scale expansion of soybean and oil palm plantations, leading to forest clearing, biodiversity loss and disease emergence, expulsion of subsistence farmers, and potential increases in food prices and emissions of carbon dioxide to the atmosphere. Investigators must consider the full range of policy options, supported by more comprehensive, flexible, and transparent assessment methods.

Integrated approaches and empirical models for investigation of parasitic diseases in northern wildlife

A decade of research has yielded a multidisciplinary approach for detection, prediction, and potential mitigation measures.

The North is a frontier for exploration of emerging infectious diseases and the large-scale drivers influencing distribution, host associations, and evolution of pathogens among persons, domestic animals, and wildlife. Leading into the International Polar Year 2007–2008, we outline approaches, protocols, and empirical models derived from a decade of integrated research on northern host–parasite systems. Investigations of emerging infectious diseases associated with parasites in northern wildlife involved a network of multidisciplinary collaborators and incorporated geographic surveys, archival collections, historical foundations for diversity, and laboratory and field studies exploring the interface for hosts, parasites, and the environment. In this system, emergence of parasitic disease was linked to geographic expansion, host switching, resurgence due to climate change, and newly recognized parasite species. Such integrative approaches serve as cornerstones for detection, prediction, and potential mitigation of emerging infectious diseases in wildlife and persons in the North and elsewhere under a changing global climate.

Climate change and infectious diseases

The worldwide upturn in the occurrence of both new (emerging) and reemerging or spreading infectious diseases highlights the importance of underlying environmental and social conditions as determinants of the generation, spread, and impact of infectious diseases in human populations. Human ecology is undergoing rapid transition. This encompasses urbanization, rising consumerism, changes in working conditions, population aging, marked increases in mobility, changes in culture and behavior, evolving health-care technologies, and other factors. Global climate change is becoming a further, and major, large-scale influence on the pattern of infectious disease transmission. It is likely to become increasingly important over at least the next halfcentury, as the massive, highinertial, and somewhat unpredictable process of climate change continues. The many ways in which climate change does and will influence infectious diseases are subject to a plethora of modifying influences by other factors and processes: constitutional characteristics of hosts, vectors and pathogens; the prevailing ambient conditions; and coexistent changes in other social, economic, behavioral, and environmental factors. This global anthropogenic process, climate change, along with other unprecedented global environmental changes, is beginning to destabilize and weaken the planet's life-support systems. Infectious diseases, unlike other diseases, depend on the biology and behavior—each often climate-sensitive—of two or more parties. Hence, these diseases will be particularly susceptible to changes as the world's climate and its climate-sensitive geochemical and ecological systems undergo change over the coming decades.

Thermal tolerance in a south-east African population of the tsetse fly Glossina pallidipes (Diptera, Glossinidae): implications for forecasting climate change impacts

For tsetse (Glossina spp.), the vectors of human and animal trypanosomiases, the physiological mechanisms linking variation in population dynamics with changing weather conditions have not been well established. Here, we investigate high- and low-temperature tolerance in terms of activity limits and survival in a natural population of adult Glossina pallidipes from eastern Zambia. Due to increased interest in chilling flies for handling and aerial dispersal in sterile insect technique control and eradication programmes, we also provide further detailed investigation of low-temperature responses. In wild-caught G. pallidipes, the probability of survival for 50% of the population at low-temperatures was at 3.7, 8.9 and 9.6 degrees C (95% CIs: +/-1.5 degrees C) for 1, 2 and 3 h treatments, respectively. At high temperatures, it was estimated that treatments at 37.9, 36.2 and 35.6 degrees C (95% CIs: +/-0.5 degrees C) would yield 50% population survival for 1, 2 and 3 h, respectively. Significant effects of time and temperature were detected at both temperature extremes (GLZ, p<0.05 in all cases) although a time-temperature interaction was only detected at high temperatures (p<0.0001). We synthesized data from four other Kenyan populations and found that upper critical thermal limits showed little variation among populations and laboratory treatments (range: 43.9-45.0 degrees C; 0.25 degrees C/min heating rate), although reduction to more ecologically relevant heating rates (0.06 degrees C/min) reduce these values significantly from approximately 44.4 to 40.6 degrees C, thereby providing a causal explanation for why tsetse distribution may be high-temperature limited. By contrast, low-temperature limits showed substantial variation among populations and acclimation treatments (range: 4.5-13.8 degrees C; 0.25 degrees C/min), indicating high levels of inter-population variability. Ecologically relevant cooling rates (0.06 degrees C/min) suggest tsetses are likely to experience chill coma temperatures under natural conditions (approximately 20-21 degrees C). The results from acute hardening experiments in the Zambian population demonstrate limited ability to improve low-temperature tolerance over short (hourly) timescales after non-lethal pre-treatments. In flies which survived chilling, recovery times were non-linear with plateaus between 2-6 and 8-12 degrees C. Survival times ranged between 4 and 36 h and did not vary between flies which had undergone chill coma by comparison with flies which had not, even after factoring body condition into the analyses (p>0.5 in all cases). However, flies with low chill coma values had the highest body water and fat content, indicating that when energy reserves are depleted, low-temperature tolerance may be compromised. Overall, these results suggest that physiological mechanisms may provide insight into tsetse population dynamics, hence distribution and abundance, and support a general prediction for reduced geographic distribution under future climate warming scenarios.

Effect of meteorological factors on clinical malaria risk among children: an assessment using village-based meteorological stations and community-based parasitological survey

Background

Temperature, rainfall and humidity have been widely associated with the dynamics of malaria vector population and, therefore, with spread of the disease. However, at the local scale, there is a lack of a systematic quantification of the effect of these factors on malaria transmission. Further, most attempts to quantify this effect are based on proxy meteorological data acquired from satellites or interpolated from a different scale. This has led to controversies about the contribution of climate change to malaria transmission risk among others. Our study addresses the original question of relating meteorological factors measured at the local scale with malaria infection, using data collected at the same time and scale.

Methods

676 children (6–59 months) were selected randomly from three ecologically different sites (urban and rural). During weekly home visits between December 1, 2003, and November 30, 2004, fieldworkers tested children with fever for clinical malaria. They also collected data on possible confounders monthly. Digital meteorological stations measured ambient temperature, humidity, and rainfall in each site. Logistic regression was used to estimate the risk of clinical malaria given the previous month's meteorological conditions.

Results

The overall incidence of clinical malaria over the study period was 1.07 episodes per child. Meteorological factors were associated with clinical malaria with mean temperature having the largest effect.

Conclusion

Temperature was the best predictor for clinical malaria among children under five. A systematic measurement of local temperature through ground stations and integration of such data in the routine health information system could support assessment of malaria transmission risk at the district level for well-targeted control efforts.

Comparative risk assessment of the burden of disease from climate change

The World Health Organization has developed standardized comparative risk assessment methods for estimating aggregate disease burdens attributable to different risk factors. These have been applied to existing and new models for a range of climate-sensitive diseases in order to estimate the effect of global climate change on current disease burdens and likely proportional changes in the future. The comparative risk assessment approach has been used to assess the health consequences of climate change worldwide, to inform decisions on mitigating greenhouse gas emissions, and in a regional assessment of the Oceania region in the Pacific Ocean to provide more location-specific information relevant to local mitigation and adaptation decisions. The approach places climate change within the same criteria for epidemiologic assessment as other health risks and accounts for the size of the burden of climate-sensitive diseases rather than just proportional change, which highlights the importance of small proportional changes in diseases such as diarrhea and malnutrition that cause a large burden. These exercises help clarify important knowledge gaps such as a relatively poor understanding of the role of nonclimatic factors (socioeconomic and other) that may modify future climatic influences and a lack of empiric evidence and methods for quantifying more complex climate-health relationships, which consequently are often excluded from consideration. These exercises highlight the need for risk assessment frameworks that make the best use of traditional epidemiologic methods and that also fully consider the specific characteristics of climate change. These include the longterm and uncertain nature of the exposure and the effects on multiple physical and biotic systems that have the potential for diverse and widespread effects, including high-impact events.

Infectious Disease in the Age of Globalization

This chapter explores the links between globalization and infectious diseases in relation to changes in four major spheres—economic, environmental, political and demographic, and technological. It highlights areas where the evidence suggests that processes of globalization have led to changes in the distribution, transmission rate, and, in some cases, management of infectious diseases.

Sustainable waste management in the UK: the public health role

This paper discusses waste management in the UK and its relationship with health. It aims to outline the role of health professionals in the promotion of waste management, and argues for a change in their role in waste management regulation to help make the process more sustainable. The most common definition of sustainable development is that by the Brundtland commission, i.e. "development that meets the needs of the present without compromising the ability of future generations to meet their own needs". Managing waste sites in a manner that minimises toxic impacts on the current and future generations is obviously a crucial part of this. Although the management of waste facilities is extremely complex, the Integrated Pollution Prevention and Control regime, which requires the input of public health professionals on the regulation of such sites, means that all waste management installations should now be operating in a fashion that minimises any toxicological risks to human health. However, the impacts upon climate change, resource use and health inequalities, as well as the effects of waste transportation, are currently not considered to be part of public health professionals' responsibilities when dealing with these sites. There is also no requirement for public health professionals to become involved in waste management planning issues. The fact that public health professionals are not involved in any of these issues makes it unlikely that the potential impacts upon health are being considered fully, and even more unlikely that waste management will become more sustainable. This paper aims to show that by only considering direct toxicological impacts, public health professionals are not fully addressing all the health issues and are not contributing towards sustainability. There is a need for a change in the way that health professionals deal with waste management issues.

Climate change and human health impacts in the United States: an update on the results of the U.S. national assessment

The health sector component of the first U.S. National Assessment, published in 2000, synthesized the anticipated health impacts of climate variability and change for five categories of health outcomes: impacts attributable to temperature, extreme weather events (e.g., storms and floods) , air pollution, water- and food-borne diseases, and vector- and rodent-borne diseases. The Health Sector Assessment (HSA) concluded that climate variability and change are likely to increase morbidity and mortality risks for several climate-sensitive health outcomes, with the net impact uncertain. The objective of this study was to update the first HSA based on recent publications that address the potential impacts of climate variability and change in the United States for the five health outcome categories. The literature published since the first HSA supports the initial conclusions, with new data refining quantitative exposure-response relationships for several health end points, particularly for extreme heat events and air pollution. The United States continues to have a very high capacity to plan for and respond to climate change, although relatively little progress has been noted in the literature on implementing adaptive strategies and measures. Large knowledge gaps remain, resulting in a substantial need for additional research to improve our understanding of how weather and climate, both directly and indirectly, can influence human health. Filling these knowledge gaps will help better define the potential health impacts of climate change and identify specific public health adaptations to increase resilience.

Climate change and human health: impacts, vulnerability, and mitigation

It is now widely accepted that climate change is occurring as a result of the accumulation of greenhouse gases in the atmosphere arising from the combustion of fossil fuels. Climate change may affect health through a range of pathways--eg, as a result of increased frequency and intensity of heat waves, reduction in cold-related deaths, increased floods and droughts, changes in the distribution of vector-borne diseases, and effects on the risk of disasters and malnutrition. The overall balance of effects on health is likely to be negative and populations in low-income countries are likely to be particularly vulnerable to the adverse effects. The experience of the 2003 heat wave in Europe shows that high-income countries might also be adversely affected. Adaptation to climate change requires public-health strategies and improved surveillance. Mitigation of climate change by reducing the use of fossil fuels and increasing the use of a number of renewable energy technologies should improve health in the near term by reducing exposure to air pollution.

Climate change and human health: impacts, vulnerability and public health

It is now widely accepted that climate change is occurring as a result of the accumulation of greenhouse gases in the atmosphere arising from the combustion of fossil fuels. Climate change may affect health through a range of pathways, for example as a result of increased frequency and intensity of heat waves, reduction in cold related deaths, increased floods and droughts, changes in the distribution of vector-borne diseases and effects on the risk of disasters and malnutrition. The overall balance of effects on health is likely to be negative and populations in low-income countries are likely to be particularly vulnerable to the adverse effects. The experience of the 2003 heat wave in Europe shows that high-income countries may also be adversely affected. Adaptation to climate change requires public health strategies and improved surveillance. Mitigation of climate change by reducing the use of fossil fuels and increasing a number of uses of the renewable energy technologies should improve health in the near-term by reducing exposure to air pollution.

Impact of regional climate change on human health

The World Health Organisation estimates that the warming and precipitation trends due to anthropogenic climate change of the past 30 years already claim over 150,000 lives annually. Many prevalent human diseases are linked to climate fluctuations, from cardiovascular mortality and respiratory illnesses due to heatwaves, to altered transmission of infectious diseases and malnutrition from crop failures. Uncertainty remains in attributing the expansion or resurgence of diseases to climate change, owing to lack of long-term, high-quality data sets as well as the large influence of socio-economic factors and changes in immunity and drug resistance. Here we review the growing evidence that climate-health relationships pose increasing health risks under future projections of climate change and that the warming trend over recent decades has already contributed to increased morbidity and mortality in many regions of the world. Potentially vulnerable regions include the temperate latitudes, which are projected to warm disproportionately, the regions around the Pacific and Indian oceans that are currently subjected to large rainfall variability due to the El Niño/Southern Oscillation sub-Saharan Africa and sprawling cities where the urban heat island effect could intensify extreme climatic events.

Climate change and human health: estimating avoidable deaths and disease

Human population health has always been central in the justification for sustainable development but nearly invisible in the United Nations Framework Convention on Climate Change negotiations. Current scientific evidence indicates that climate change will contribute to the global burden of disease through increases in diarrhoeal disease, vector-borne disease, and malnutrition, and the health impacts of extreme weather and climate events. A few studies have estimated future potential health impacts of climate change but often generate little policy-relevant information. Robust estimates of future health impacts rely on robust projections of future disease patterns. The application of a standardized and established methodology has been developed to quantify the impact of climate change in relation to different greenhouse gas emission scenarios. All health risk assessments are necessarily biased toward conservative best-estimates of health effects that are easily measured. Global, regional, and national risk assessments can take no account of irreversibility, or plausible low-probability events with potentially very high burdens on human health. There is no "safe limit" of climate change with respect to health impacts as health systems in some regions do not adequately cope with the current climate variability. Current scientific methods cannot identify global threshold health effects in order for policymakers to regulate a "tolerable" amount of climate change. We argue for the need for more research to reduce the potential impacts of climate change on human health, including the development of improved methods for quantitative risk assessment. The large uncertainty about the future effects of climate change on human population health should be a reason to reduce greenhouse gas emissions, and not a reason for inaction.

North Atlantic weather oscillation and human infectious diseases in the Czech Republic, 1951-2003

Longitudinal correlation between the North Atlantic Oscillation large-scale weather system (NAO) and the annual incidence rate of 14 viral, bacterial and protozoan national notifiable human diseases in the Czech Republic was examined. In simple correlation, cases of salmonellosis, erysipelas, infectious mononucleosis and toxoplasmosis were positively correlated with the winter NAO index, while hepatitis A and shigellosis were negatively correlated, and the other diseases tested (rubella, mumps, chickenpox, tick-borne encephalitis, Lyme borreliosis, leptospirosis, tularemia and scarlet fever) were uncorrelated with NAO. However, 8 of the 14 diseases also revealed a significant time trend, either increasing (infectious mononucleosis, salmonellosis, erysipelas, toxoplasmosis) or decreasing (hepatitis A, scarlet fever, leptospirosis, shigellosis) during the period. When the effect of NAO on incidence of the diseases was then controlled for calendar year using partial correlation analysis and detrended regression, only toxoplasmosis and infectious mononucleosis were found significantly positively correlated with the NAO when the index was lagged 1 or 2 years, and leptospirosis was correlated negatively with a lag of 2 years. Large-scale weather changes as described by NAO therefore do not seem to be a crucial factor in the fluctuation of annual incidence rate of the majority of tested infectious diseases in the Czech Republic, while other factors, especially social and public health circumstances, are obviously more important.

Nonstationary influence of El Niño on the synchronous dengue epidemics in Thailand

BACKGROUND

Several factors, including environmental and climatic factors, influence the transmission of vector-borne diseases. Nevertheless, the identification and relative importance of climatic factors for vector-borne diseases remain controversial. Dengue is the world's most important viral vector-borne disease, and the controversy about climatic effects also applies in this case. Here we address the role of climate variability in shaping the interannual pattern of dengue epidemics.

METHODS AND FINDINGS

We have analysed monthly data for Thailand from 1983 to 1997 using wavelet approaches that can describe nonstationary phenomena and that also allow the quantification of nonstationary associations between time series. We report a strong association between monthly dengue incidence in Thailand and the dynamics of El Niño for the 2-3-y periodic mode. This association is nonstationary, seen only from 1986 to 1992, and appears to have a major influence on the synchrony of dengue epidemics in Thailand.

CONCLUSION

The underlying mechanism for the synchronisation of dengue epidemics may resemble that of a pacemaker, in which intrinsic disease dynamics interact with climate variations driven by El Niño to propagate travelling waves of infection. When association with El Niño is strong in the 2-3-y periodic mode, one observes high synchrony of dengue epidemics over Thailand. When this association is absent, the seasonal dynamics become dominant and the synchrony initiated in Bangkok collapses.

Climate change and the recent emergence of bluetongue in Europe

Bluetongue, a devastating disease of ruminants, has historically made only brief, sporadic incursions into the fringes of Europe. However, since 1998, six strains of bluetongue virus have spread across 12 countries and 800 km further north in Europe than has previously been reported. We suggest that this spread has been driven by recent changes in European climate that have allowed increased virus persistence during winter, the northward expansion of Culicoides imicola, the main bluetongue virus vector, and, beyond this vector's range, transmission by indigenous European Culicoides species - thereby expanding the risk of transmission over larger geographical regions. Understanding this sequence of events may help us predict the emergence of other vector-borne pathogens.

Environmental health implications of global climate change

This paper reviews the background that has led to the now almost-universally held opinion in the scientific community that global climate change is occurring and is inescapably linked with anthropogenic activity. The potential implications to human health are considerable and very diverse. These include, for example, the increased direct impacts of heat and of rises in sea level, exacerbated air and water-borne harmful agents, and--associated with all the preceding--the emergence of environmental refugees. Vector-borne diseases, in particular those associated with blood-sucking arthropods such as mosquitoes, may be significantly impacted, including redistribution of some of those diseases to areas not previously affected. Responses to possible impending environmental and public health crises must involve political and socio-economic considerations, adding even greater complexity to what is already a difficult challenge. In some areas, adjustments to national and international public health practices and policies may be effective, at least in the short and medium terms. But in others, more drastic measures will be required. Environmental monitoring, in its widest sense, will play a significant role in the future management of the problem.

Effect of topography on the risk of malaria infection in the Usambara Mountains, Tanzania

We investigated whether the risk of infection with malaria parasites was related to topography in the Usambara Mountains, Tanzania. Clinical surveys were carried out in seven villages, situated at altitudes from 300 m to 1650 m. Each village was mapped and incorporated into a Digital Terrain Model. Univariate analysis showed that the risk of splenomegaly declined with increasing altitude and with decreasing potential for water to accumulate. Logistic regression showed that altitude alone could correctly predict 73% of households where an occupant had an enlarged spleen or not. The inclusion of land where water is likely to accumulate within 400 m of each household increased the accuracy of the overall model slightly to 76%, but significantly improved predictions between 1000 m and 1200 m, where malaria is unstable, and likely to be epidemic. This novel approach illustrates how topography could help identify local areas prone to epidemics in the African highlands.

Predicting the geography of species' invasions via ecological niche modeling

Species' invasions have long been regarded as enormously complex processes, so complex as to defy predictivity. Phases of this process, however, are emerging as highly predictable: the potential geographic course of an invasion can be anticipated with high precision based on the ecological niche characteristics of a species in its native geographic distributional area. This predictivity depends on the premise that ecological niches constitute long-term stable constraints on the potential geographic distributions of species, for which a sizeable body of evidence is accumulating. Hence, although the entire invasion process is indeed complex, the geographic course that invasions are able to take can be anticipated with considerable confidence.

Global change and human vulnerability to vector-borne diseases

Global change includes climate change and climate variability, land use, water storage and irrigation, human population growth and urbanization, trade and travel, and chemical pollution. Impacts on vector-borne diseases, including malaria, dengue fever, infections by other arboviruses, schistosomiasis, trypanosomiasis, onchocerciasis, and leishmaniasis are reviewed. While climate change is global in nature and poses unknown future risks to humans and natural ecosystems, other local changes are occurring more rapidly on a global scale and are having significant effects on vector-borne diseases. History is invaluable as a pointer to future risks, but direct extrapolation is no longer possible because the climate is changing. Researchers are therefore embracing computer simulation models and global change scenarios to explore the risks. Credible ranking of the extent to which different vector-borne diseases will be affected awaits a rigorous analysis. Adaptation to the changes is threatened by the ongoing loss of drugs and pesticides due to the selection of resistant strains of pathogens and vectors. The vulnerability of communities to the changes in impacts depends on their adaptive capacity, which requires both appropriate technology and responsive public health systems. The availability of resources in turn depends on social stability, economic wealth, and priority allocation of resources to public health.

Effect of temperature on the development of the aquatic stages of Anopheles gambiae sensu stricto (Diptera: Culicidae)

Global warming may affect the future pattern of many arthropod-borne diseases, yet the relationship between temperature and development has been poorly described for many key vectors. Here the development of the aquatic stages of Africa's principal malaria vector, Anopheles gambiae s.s. Giles, is described at different temperatures. Development time from egg to adult was measured under laboratory conditions at constant temperatures between 10 and 40 degrees C. Rate of development from one immature stage to the next increased at higher temperatures to a peak around 28 degrees C and then declined. Adult development rate was greatest between 28 and 32 degrees C, although adult emergence was highest between 22 and 26 degrees C. No adults emerged below 18 degrees C or above 34 degrees C. Non-linear models were used to describe the relationship between developmental rate and temperature, which could be used for developing process-based models of malaria transmission. The utility of these findings is demonstrated by showing that a map where the climate is suitable for the development of aquatic stages of A. gambiae s.s. corresponded closely with the best map of malaria risk currently available for Africa.

Lutzomyia vectors for cutaneous leishmaniasis in Southern Brazil: ecological niche models, predicted geographic distributions, and climate change effects

Geographic and ecological distributions of three Lutzomyia sand flies that are cutaneous leishmaniasis vectors in South America were analysed using ecological niche modelling. This new tool provides a large-scale perspective on species' geographic distributions, ecological and historical factors determining them, and their potential for change with expected environmental changes. As a first step, the ability of this technique to predict geographic distributions of the three species was tested statistically using two subsampling techniques: a random-selection technique that simulates 50% data density, and a quadrant-based technique that challenges the method to predict into broad unsampled regions. Predictivity under both test schemes was highly statistically significant. Visualisation of ecological niches provided insights into the ecological basis for distributional differences among species. Projections of potential geographic distributions across scenarios of global climate change suggested that only Lutzomyia whitmani is likely to be experiencing dramatic improvements in conditions in south-eastern Brazil, where cutaneous leishmaniasis appears to be re-emerging; Lutzomyia intermedia and Lutzomyia migonei may be seeing more subtle improvements in climatic conditions, but the implications are not straightforward. More generally, this technique offers the possibility of new views into the distributional ecology of disease, vector, and reservoir species.

Tick-borne encephalitis in north-eastern Poland in 1997-2001: a retrospective study

The aim of this study was to characterize the epidemiology and clinical features of tick-borne encephalitis in north-eastern Poland. Clinical and epidemiological data were analysed of patients hospitalized with the diagnosis in the Department of the Infectious Diseases and Neuroinfections of the Medical University in Bialystok in 1997-2001. Tick-borne encephalitis was diagnosed in 152 patients: 51 (34%) presented with meningitis, 89 (59%) with meningoencephalitis and 12 (8%) with meningoencephalomyelitis. Headache (84%) and fever (81%) were the most common symptoms. Meningeal signs were present in 137 patients (90%). Most common neurological abnormalities were: Oppenheim and Babinski signs (74 patients, 49%), ataxia (37, 24%), impaired consciousness (37, 24%) and pareses (16, 10%). Of patients examined, 146 (96%) had raised pleiocytosis, frequently accompanied by high cerebrospinal fluid protein concentration (90%), raised erythrocyte sedimentation rate (65%), peripheral blood leucocytosis (26%) and increased aminotransferase activity (16%). There was only 1 forest worker among the patients. Tick-borne encephalitis remains common in north-eastern Poland but, possibly because of effective vaccination, it has virtually disappeared among forest employees. The diagnosis appears difficult in some cases, as meningeal signs may not be present and laboratory findings may not be suggestive of a viral infection.

Hot topic or hot air? Climate change and malaria resurgence in East African highlands

Climate has a significant impact on malaria incidence and we have predicted that forecast climate changes might cause some modifications to the present global distribution of malaria close to its present boundaries. However, it is quite another matter to attribute recent resurgences of malaria in the highlands of East Africa to climate change. Analyses of malaria time-series at such sites have shown that malaria incidence has increased in the absence of co-varying changes in climate. We find the widespread increase in resistance of the malaria parasite to drugs and the decrease in vector control activities to be more likely driving forces behind the malaria resurgence.

Climate warming and disease risks for terrestrial and marine biota

Infectious diseases can cause rapid population declines or species extinctions. Many pathogens of terrestrial and marine taxa are sensitive to temperature, rainfall, and humidity, creating synergisms that could affect biodiversity. Climate warming can increase pathogen development and survival rates, disease transmission, and host susceptibility. Although most host-parasite systems are predicted to experience more frequent or severe disease impacts with warming, a subset of pathogens might decline with warming, releasing hosts from disease. Recently, changes in El Niño-Southern Oscillation events have had a detectable influence on marine and terrestrial pathogens, including coral diseases, oyster pathogens, crop pathogens, Rift Valley fever, and human cholera. To improve our ability to predict epidemics in wild populations, it will be necessary to separate the independent and interactive effects of multiple climate drivers on disease impact.

Population, environment, disease, and survival: past patterns, uncertain futures

Societies are exploring what sustainable development means for development choices. Increasingly, we recognise that human population health is not just an input to socioeconomic development, but is an essential outcome, and, over time, a marker of sustainability. There has been recent attention to how stocks of social and human capital precondition gains in population health. However, recognition of how environmental change can limit health and survival has been slower. Over many millennia, disease and longevity profiles in populations have reflected changes in environmental conditions and, often, excedances of carrying capacity. Today, population growth and the aggregated pressures of consumption and emissions are beginning to impair various global environmental systems. The research tasks in detecting, attributing, and projecting the resultant health effects are complex. Have recent health gains, in part, depended on depleting natural environmental capital? Population health sciences have a crucial contribution to make to the sustainability project.