The Intersection of Environmental Health and Infectious Disease Control: Addressing the Role of Climate Change in Emerging Global Health Threats

The central role of environmental health in addressing infectious disease threats is increasingly recognized across the spectrum of public health and encompassed within a security framework. Emerging and re-emerging infectious diseases, whose effects are no longer confined to specific populations or geographic areas, are the new global health threats [1,2]. The future increasing threats to human health in many areas, such as Asia, South America, and Central and Eastern Europe, due to climate change were recently described by a research group [3]. The report concluded that climate change has already demonstrated its role in altered distributions of infectious diseases, such as malaria, dengue and hantavirus [4].

This essay begins with an examination of a more concrete and specific aspect of this theme. The objective is to discuss current and future diseases that are causing global health concerns and are exacerbated by climate change, as well as link environmental health and infectious disease control. The objectives of the essay are fourfold: to discuss the growing concerns about severe acute respiratory syndrome, avian influenza, and biological terrorism using agents such as smallpox in the context of global public health; to outline the central roles of environmental health and infectious disease control in the global public health response; to discuss the paucity of risk management research in attempts to project the future length and severity of epidemics and pandemics; and to address the societal need for improved scientific understanding of links between environmental health vulnerability, climate change, and infectious disease emergence. The re-emergence of H5N1 in humans further suggests the urgent need for the development of knowledge bases that intersect environmental health and infectious disease concepts for integrated public health adaptation responses to potential emerging health threats.

The global community has witnessed an unprecedented number of emerging infectious disease outbreaks in the past few decades, many of them driven by environmental factors. Today, human populations are faced with an increasingly interconnected global environment, climate change, and broader land use change. Recent evidence has demonstrated that climate change and global warming can have profound effects on the spread of infectious diseases and disease burden, especially in developing countries that are most vulnerable. Many global efforts to reduce such threats continue to focus on dealing with diseases according to traditional treatment approaches; these approaches do not often include the important contribution that environmental health factors make to the global disease burden, now or in the future [5,6].

Over the past few decades, a wide range of studies have shown the importance of incorporating environmental health perspectives into solutions for earlier problems, such as large-scale water projects, novel agricultural practices, and community-based vector control programs for reducing disease risks for mosquito-borne parasitic and viral diseases in developing countries [7-9]. Good health, especially where infectious absenteeism accounts for a major portion of social and financial costs, is dependent upon many variables beyond socially and behaviorally rooted and personal biological determinants. International and national policymakers and practitioners in all areas of environmental and public health are increasingly required to understand the need to look at broader determinants of health than have previously been the focus of reducing the economic and health impacts of infectious disease.

Understanding the intersection of environmental health and infectious disease control

However, the trajectory of health reform and prioritization of social determinants of health have irrefutably occurred against the backdrop of contemporary intersecting environmental health and infectious disease dynamics, the so-called Anthropocene, in which our planet—its air quality, water quality, and biodiversity—is also marred by what many have characterized as global environmental change. This has profound implications for infectious disease dynamics and, in turn, the core principles of infectious disease control. Considering these interactions is also fundamental to achieving the aspiration of SDG 3.3, in which undernutrition, communicable diseases, and non-communicable diseases are recognized as interconnected issues with common behavioral, social, economic, environmental, and health determinants [10,11]. In other words, this investigation of health and the environment is not confined to relatively exotic, far-flung creatures, others, or those exposed to their ills but is interwoven in the very realities of urbanization and globalization characterized by social distancing and social division.

The interactions between human health and ecosystems and between the social and natural sciences for addressing these concerns have been variously characterized in contemporary literature as a range of terms, ranging from the ecosystem approach to one health. Unlike many definitions from expert-informed consensus processes that purport to simplify, unify, and delimit the scope of the phenomenon at hand, the introduction to this reading guide to environment and health specifically notes incoherence in the terms deployed to designate them. Perhaps they argue that the interrelated issues are intentionally complex, intentional in that they stem from multiple plausible dispositions, emphases, and interpretations, and complex in that of necessity; the concepts are contested, shifting, and aligned with the politics of stakeholders from a range of backgrounds. We use a broader framing because it best reflects the required ecological perspective to understand declining health and well-being. Additionally, external, macro-structural conditions also mediate health standards, which are less amenable to influence through individual behavioral change. It is not that individual responsibility does not play a role in poor health outcomes and well-being but that a broader picture of social and environmental factors must be taken into account. A broader, multidisciplinary framing also opens up the possibility for preventative approaches rather than dealing predominantly with individual health consumers.

Key concepts and definitions

Environment as a determinant of health: when we speak of the environment as a determinant of health, we are referring to an approach that encompasses all the external and internal determinants of health. These include personal habits, work environment, water, air, food, schools, workplaces, communities, country, and global conditions. This broader concept approach includes not only our physical environment but also its social, economic, and political dimensions—in other words, the physical and biological determinants of human health and the effects of the environment on these determinants. Ecosystem approach and environmental determinants of health Interactions between environmental determinants of health can result in complex and multiplicative impacts on ecosystems and human health. Upsetting environmental determinants can set off a chain reaction that can have far-reaching repercussions. At an ecosystem level, human health is one of seven clusters of outcome areas; other areas include cultural, economic, ethical, social, political, and ecological indices. At the root of this ecosystem approach is the contention that attention to planetary health can contribute to greater equity between and among the length and breadth of human and non-human life. Because of the potential for detrimental impacts on ecosystems, we cannot afford to disregard the correlation between human health and global change (particularly climate change). Because of the potential for health impacts on human populations, we cannot afford to overlook such interactions in our discussions of public health.

The impact of climate change on infectious disease transmission

While climate change is likely to impact a wide array of hazards related to infectious disease, it is the potential for vector-borne emerging infectious disease that has garnered the greatest attention and inspired the most speculation. This concern is not unwarranted, and indeed, we are confident that many of the effects that climate change will have in potentially accelerating the spread of vector-borne infectious diseases will be profound and highly concerning. But this is not to say that all of the concerns are justified or that in the end, risk analyses that move away from purely parasitic models towards one of understanding the entire dynamic of a host-vector-pathogen triad will not be entirely unexpected in their results [12,13]. Dynamics in emerging diseases are complex, involving many different factors and many different disciplines, and the role that climate change will have in determining that very complex future is similarly going to be quite complex. While there has been substantial speculation on the ways in which climate change may impact infectious disease, there have been correspondingly very few attempts to quantify the degree to which climate does or does not present a significant barrier to disease spread. Providing some of the quantitative rules that constrain those infectious disease baseline rates of incidence and types is desirable, especially for those slowly emerging infectious diseases that might be helped in their emergent waves by the changing climate.

Direct and indirect effects

Several mechanisms have been proposed for the climate-disease connection. For vector-borne infectious diseases, such as malaria, diseases transmitted by ticks carrying Lyme disease, and other illnesses, the survival, feeding, development, and regulatory interactions of many insect and arthropod vectors are influenced by climatic conditions [14,15]. In relation to temperature, increased warmth logically leads to increased growth and survival of such vectors, which in turn increases the rate of vector-host contact and speed of pathogen development within the vector [14]. These changes lengthen the vector's active transmission period and extend the geographic range of the vector and the pathogen it carries. Rainfall, temperature, and relative humidity are also crucial determinants of vector population size and shape the levels of human, animal, and wildlife host immunity and density that affect pathogen flows between these entities. Growing periods and phenological interrelationships with climate factors drive food and agricultural production systems that, in turn, drive vectors targeted to disease events [16].

The lessons that the literature presents around the impacts of climate change on the distributions of existing infectious diseases and the risk of new and exotic diseases are also complemented by a growing body of work that exemplifies how sustainability and environmental health impacts are translated into infectious disease outbreaks. We provide four detailed examples of environmental health challenges in different countries and discuss their role in different infectious disease system structures. While the examples are diverse in geographic area and environmental specificity, they all highlight the importance of the socio-ecological context in altered land-use systems and climate change.

While environmental land use and climate factors can act to increase the transmission and distribution of infectious diseases, public health intervention programs can have a great impact on limiting the spread of these and other pathogens. For example, successful programs have supported significant drops in malaria-related morbidity and mortality. Furthermore, theories have been developed that suggest that the increase in dengue fever, associated with climate change, could be buffered by regional health interventions. However, without a better understanding of the role that climate change plays in the emergence and spread of infectious diseases, decision-makers have been unable to develop effective disease control programs. Climate change may impact the timing and geographic range of many infectious diseases. This can result in both increases in the time of overlap between these pathogens, as well as in new geographic regions being colonized by these diseases for the first time in recorded human history. Since many diseases are growing in prevalence, these changes are likely to exacerbate these trends. Preventative medicine and public health planning are essential to controlling the future impacts of emerging infectious diseases.

Malaria in Sub-Saharan Africa

Malaria is a useful case study for the effect of climate change on emerging infectious diseases. Malaria has been a focal point for many studies on the relationship between climate and infectious diseases, and biomathematical models have been used to express the subtle ways in which changing climate patterns alter the timing and intensity of malaria transmission [17,18]. Indeed, climate variations over the years will directly affect transmission dynamics as the parasite moves through its life cycle. The result of the interactions with climate, threshold climatic effects on vectors, and the complexities of stochastic geography combine to produce the difficult problem of vectors being drawn to ecotones. The habitats of many of these zones of transmission are products of geography, including river deltas, the urban areas of Port Moresby, Papua New Guinea, and the rice fields of much of equatorial Asia, Africa, and Latin America [19]. The habitats of these populations are defined by both the influx of P. falciparum into the cities during the first rains and the development of unstable garbage in the stagnant water, which allows the mosquitoes to undergo rejuvenation and hatching. Each of these areas, through the uniquely geographical parameters that alternately drive them to their hazardous states and then allow them to revert, provide the three critical components: host, vector, and parasite. Sub-Saharan Africa is an ideal ecological niche, as defined by the granular climatic conditions and human heterogeneities that dictate that 90-92% of the cases reported in any given year result from P. falciparum [20,21]. The final elements that further compound the extreme vulnerability of the African region are both ecological and socio-economic in nature. The unique physical parameters regarding vector, parasite, and host are matched solely by the challenges presented by these.

Leptospirosis in South Asia

For instance, in South Asia, the response to the increasing spread of leptospirosis, particularly after monsoon floods, demonstrates a successful intervention model. Coordinated efforts included widespread public awareness campaigns, improved sanitation, and rapid-response healthcare services. These measures led to a notable decrease in infection rates, showing how swift, targeted action can limit disease transmission in flood-prone areas.

In contrast, dengue fever control efforts in Southeast Asia faced challenges due to resource constraints and socioeconomic factors despite the use of vector control strategies. These obstacles emphasize the need for adaptable strategies that consider local socio-economic and environmental conditions.

Chagas disease in Latin America

Additionally, we highlight how failed attempts in Latin America to manage Chagas disease reveal limitations in intervention scalability, particularly in areas experiencing rapid deforestation. These areas have witnessed the spread of disease vectors to new regions, underscoring the importance of integrating land-use planning with public health measures to limit disease transmission.

These detailed analyses show how public health programs can both mitigate and face challenges in controlling climate-related infectious diseases. By understanding the factors that contributed to both the successes and limitations, decision-makers can better design adaptable and scalable intervention models that consider the unique socio-ecological conditions in each region.

Effective responses will address the risks to health associated with climate change as well as the underlying social and environmental determinants of these changes, using an evidence-based approach that will involve mitigation and adaptation strategies. Many analysts also feel it is important to integrate public health planning at the community, regional, national, and global levels with climate action frameworks. Central to current approaches to climate protection are proposals to either reduce greenhouse gas emissions or create technological mechanisms or markets aimed at reducing these emissions as quickly and effectively as possible. It is also being recognized that these approaches need to address differential vulnerabilities in society by incorporating the principles of health equity, participation, precaution, and the social determinants of health in their planning and implementation.

Proposed strategies articulate visions and goals that aim to not only reduce global greenhouse gas emissions, but also to increase the health and well-being of societies by considering broader determinants of health in a variety of sectors. Innovative strategies that link human health to environmental protection may be able to reduce activities that lead to climate change while more effectively enhancing human and environmental health. These strategies emphasize partnerships among the public health, natural resource management, trade, and the economics community. The public health community contends that interventions to reduce infectious disease and enhance environmental health can also lead to steps that decrease the greenhouse gases that are a major cause of climate change. These alliances can simultaneously become net cost savings, improve economic growth, and reduce poverty. These coalitions can also use existing national and international mechanisms to carry out action. Local initiatives, from using stormwater design to developing effective participatory urban infrastructures in low- and middle-income countries, are being researched and tried with the support of multiple agencies.

Policy recommendations

With increasing human mobility, urban expansion, and interactions among human, animal, and environmental systems, health issues are deeply interconnected. Policy solutions, therefore, must address both environmental health and infectious disease prevention holistically. Additionally, an evidence-based approach to policy reform is essential, given the need for both current data review and new data acquisition. Based on our analysis, we present the following detailed short-term and long-term policy recommendations, with examples for contextual applicability.

Short-term policy recommendations

Invest in research, surveillance and community engagement: Allocate funds toward research focused on understanding the links between environmental factors and infectious disease transmission. For instance, community-based surveillance initiatives in coastal cities can monitor climate-driven diseases like leptospirosis and cholera, helping to tailor interventions that respond to seasonal outbreaks. Collaborative community engagement can build local capacity and resilience, especially in high-risk rural and peri-urban areas.

Enlist nationals for multidisciplinary training and community outreach: Ensure that frontline workers, including agricultural and wildlife specialists, are trained to engage effectively with local communities. For example, training ecologists and conservationists to recognize disease symptoms in livestock or wildlife and communicate risks to farmers can bridge knowledge gaps between environmental changes and zoonotic disease risks. This approach can be implemented in contexts with high wildlife-human interaction, such as regions bordering conservation areas.

Joint burden addressal with tactical response plans: Develop tactical response plans that address both environmental health and disease prevention on military installations and surrounding communities. For instance, creating heat action plans that include disease prevention measures for military bases in high-temperature regions can reduce risks for heat-related illnesses and vector-borne diseases like dengue, especially in subtropical zones.

Long-term policy recommendations

Enhance inter-agency collaboration for broader impact: Foster collaboration between public health agencies and environmental organizations, both domestically and internationally. For example, joint initiatives between the CDC and international agencies could address climate-sensitive diseases like malaria and Rift Valley fever through cross-border disease monitoring and response efforts.

Build resilient health interventions for long-term sustainability: Develop adaptable health interventions that engage local, national, and international stakeholders in managing the interconnected impacts of climate and disease. For instance, partnerships between governments and NGOs can establish long-term health programs that address both immediate needs, such as vaccine distribution, and longer-term resilience, like public education on disease prevention and environmental conservation.

Shift toward performance-based objectives with upstream interventions: Implement performance metrics that not only evaluate immediate health outcomes but also address the root causes of disease emergence. For example, public health interventions in urban areas prone to flooding could focus on improved sanitation infrastructure to prevent waterborne diseases, reducing the likelihood of outbreaks in these high-risk areas.

Target vulnerable populations for equitable health access: Prioritize vulnerable groups, particularly those most impacted by climate and health extremes, by engaging communities directly in policy design and implementation. For instance, policies in low-lying coastal villages could focus on creating early warning systems and health response plans for climate-sensitive diseases, tailored specifically to community needs.

Ladder policy through geo-political strata for scalable impact: Implement these policy actions progressively at community, county, national, and global levels to ensure a cohesive approach. For example, a regional policy addressing disease surveillance in Central Africa could be scaled up to national levels, eventually integrating with global health security initiatives. This hierarchical approach supports local adaptation while aligning with broader health security goals.

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