The Contextual Determinants of Malaria

Elizabeth A. Professor Casman, Hadi Professor Dowlatabadi, Elizabeth A. Professor Casman, Hadi Professor Dowlatabadi

• Publisher: Routledge
• Year: 2010
• ISBN:
  9781136523045
• Edition: 1
• Topic: Medicine
• Subtopic: Public Health, Administration & Care

As malaria and other tropical diseases continue their resurgence, questions about the potential impacts of environmental and demographic factors are becoming more critical. Recent attempts to understand the increase in malaria incidence often acknowledge the importance of social, economic and other contextual variables, but fail to explicitly incorporate them into models or consider how they evolve in relation to one another. This problem is of crucial interest to the climate policy community, which has been buffeted by claims and counter-claims concerning the impact of climate change on malaria. This important volume examines the contextual determinants of malaria and attempts to develop methods for incorporating them into projections of future incidence. Internationally renowned health specialists, economists, and other social scientists provide regional and global perspectives on risk modeling, the history of eradication efforts, current determinants (including environmental, social, and economic factors), and prospects for new vaccines and drugs. The Contextual Determinants of Malaria argues that an association of climate change with increased malaria incidence will have at least as much to do with human aging, poverty, urbanization, and population movement as with a rise in global temperatures. By placing climate in this perspective, The Contextual Determinants of Malaria focuses attention on the public health needs most critical in both the immediate and long-term future. It encourages multidisciplinary analysis of malaria control, and improves our understanding of the interactions of the diverse range of factors involved in the incidence and spread of the disease.

PART 1

Malaria and Climate Change: Issues and Analytic Tools

Chapter 1

International Efforts To Understand the Link between Climate Change and Malaria

Anthony J. McMichael and R. Sari Kovats

In this chapter, we describe the Intergovernmental Panel on Climate Change (IPCC) and its process for evaluating the current science on the health impacts of climate change. IPCC is charged with carrying out systematic reviews and assessments of the relevant published scientific literature and with publishing formal reports of its assessments. Three reports have been published: in 1991, 1996, and 2001. Since the U.N. Framework Convention on Climate Change, forged at the 1992 U.N. Conference on Environment and Development in Rio de Janeiro, Brazil, IPCC has been the main source of scientific information and advice to governments within that convention.

Early IPCC assessments of changes in potential malaria transmission relied heavily on the results of the MIASMA model, which estimates how transmissibility would alter in response to changes in climate that affect the biology of mosquitoes and malaria parasites (Martens 1998). These assessments were influential in bringing the issue of the health implications of climate change into focus. This type of modeling, however, should be extended to take into account projections of social, economic, and demographic changes. For example, future assessments of health impacts could incorporate plausible scenarios of socioeconomic development (such as those as recently developed and proposed by IPCC) in a systematic effort to include these important contextual variables.

The IPCC Review Process

During the 1980s, several international conferences addressed the emerging prospect of global climate change occurring in response to the ongoing, accelerated buildup of anthropogenic greenhouse gases in the lower atmosphere (troposphere). Additional attention was focused on this issue by the newly forged international recognition of the hazards posed by human-induced stratospheric ozone depletion and by the emerging commitments to multilateral action to curb the release of ozone-destroying gases, especially chlorofluorocarbons. The Montreal Protocol was adopted in 1987 for the control of ozone-destroying substances.

The manifest complexity of the anticipated global climate change process and of the mechanisms by which it might affect various natural and societal systems suggested the need for an international, multidisciplinary scientific review and assessment. This endeavor would be a source of continuing information for national governments and policymakers. IPCC was thus established in 1988 and exists under the aegis of the World Meteorological Organization (WMO) and the U.N. Environment Programme. Its secretariat is located within the WMO in Geneva, Switzerland.

Approximately 2,000 scientists contribute to the IPCC reports as lead authors in chapter teams; they work on a volunteer basis, and national governments pay their participation costs. These scientists are organized in three working groups. Working Group I addresses the science of the climate change process and the modeled predictions of future climate scenarios in response to various scenarios of future greenhouse gas emissions. Working Group II addresses the impacts of climate change and the prospects for adaptive reduction of those impacts. Working Group III addresses the social, economic, and policy dimensions of climate change impacts and their mitigation.

The chapter teams are assembled by the co-chairs of the IPCC Working Groups from nominations received from national governments. This process must weigh the need for topic and disciplinary expertise against the need for balanced international representation. Various contributing authors (identified primarily but not exclusively via the network of lead authors) also make specific expert contributions to the text drafts.

The IPCC review process is open, participatory, and accountable. The essential task is scientific review by consensus. The IPCC chapter teams do not carry out research in their own right. Their task is to review the published scientific literature, a process which takes approximately two years for each review cycle. The draft chapters are eventually sent to a wide range of scientists, who serve as external peer reviewers. The reviewers’ comments are then systematically considered by the lead authors in the presence of the chapter’s two review editors, who must confirm to the Working Group that the review comments have been responded to satisfactorily. The development of this broad-based, peer-reviewed, and increasingly transparent procedure of consensual scientific review provides a workable model of how to minimize the influence of vested interests in the assessment of such intrinsically complex, political, and commercially sensitive topics. The IPCC review process has thus effectively neutralized the partisan influence of “bought science,” that is, the substantial conservative interests of the coal, oil-producing, petrochemical, and automotive industries. This neutralization is achieved not by exclusion but by dilution of the full spectrum of partisan views within a broad-based, open process.

In its recent work, IPCC has sought to standardize the work of the various chapter teams by specifying crosscutting issues or themes that should be addressed. Within Working Group II, for example, the Third Assessment Report pays systematic attention to the handling and communication of scientific uncertainty; to considerations of how anticipated impacts and their avoidance could affect sustainable development and international equity; to the implications for social decisionmaking (within a decision-analytic framework); and, where possible, to the estimation of the economic costs of impacts and adaptive strategies.

The IPCC Analysis of Health Impacts

The First Assessment Report had relatively little to say about the potential impact of climate change on human health. That topic evidently was a blind spot in the collective eye of climate change science in the late 1980s. However, by the early 1990s, recognition of the potential importance of this topic was growing. Consequently, both the Second and Third Assessment Reports have contained stand-alone chapters on human health impacts.

The published scientific literature on the health impacts of climate change was relatively modest throughout the 1990s. Indeed, over previous decades, epidemiologists had carried out relatively few conventional studies of how natural variations in climatic conditions affected human health. Because the weather is always with us and is not substantively modifiable by human intervention, it drew little interest from public health scientists. However, the dual stimuli of the prospect of global climate change and of the rapidly accruing new knowledge about the quasiperiodic cycles of the El Niño system and other regional climatic oscillations (see Chapter 11) drew attention to the importance of studying climate variation, climate change, and human health.

The recognized range of likely health impacts of climate change is considerable and diverse. It includes the direct impacts of thermal stress (heat waves and cold spells), meteorologically modulated air pollution, and weather disasters (tropical cyclones, storms, floods, and droughts). It also includes a wider range of less direct, often ecologically mediated impacts such as geographic and temporal changes in the transmission patterns of vector-borne and other infectious diseases; changes in regional yields of agriculture and, perhaps, ocean fisheries (and hence in the nutrition and health of local dependent populations); and the diverse health consequences of population displacement (for example, due to a rise in sea level or to declining agroecosystems) and economic dislocation.

For only several of these health outcomes had the likely impacts of climate change been systematically and quantitatively assessed. By the mid-1990s, early attempts at modeling health impacts had been published for heat wave–associated mortality, malaria, and dengue fever (Martens et al. 1995; Martens, Jetten, and Focks 1997). Perhaps not surprisingly, in the health impact chapters of the IPCC reports, considerable emphasis has been placed on the issue of how climate change is likely to affect potential patterns of malaria transmission. It is, after all, one of the world’s great (and currently increasing) public health problems, affecting several hundred million people every year and causing approximately 1 million deaths, mostly in children. Furthermore, the basic relationship of malaria transmission to temperature and humidity was worked out in the 1950s (Macdonald 1957), and it has long been understood that climatic conditions set the ultimate boundaries for malaria transmission and that shorter-term climate variations affect the local patterns and cycles of transmission.

The IPCC Analysis of Malaria Transmissibility

Each IPCC health impact team reviews three categories of scientific evidence for each health outcome:

1. the accrued empirical evidence that describes the climate-disease relationship and any associated theory that has evolved around that knowledge;

2. any evidence that recent climatic trends (regardless of whether they are human-induced) have been associated with changes in health outcome patterns; and

3. the results of formal scenario-based modeling of potential future changes in the geography, seasonality, or rates of occurrence of the health outcome.

Because of space constraints within each IPCC chapter, a detailed review of the evidence is not possible. Typically, the first category above has been dealt with summarily in the chapter text, even though the lead authors for each particular health outcome category are usually knowledgeable about that dimension of evidence.

Historically, for malaria, a great deal of evidence has been published about its relationship to climatic and environmental conditions. However, much of this reporting has been local and episodic. Few systematic analyses exist of historical patterns and trends in malaria transmission in relation to climatic variation or climate change.

In the Second Assessment Report, considerable emphasis was paid to several early mathematical modeling studies of the impact of climate change on future potential malaria transmission (IPCC 1996). These comprised both statistical and process (or biological) models that produced estimates of how the geographic boundaries of potential malaria transmission would change under specified climate change scenarios. From this basis, it was possible to discuss the approximate shift in the proportion of the world population living in geographic zones of potential transmission.

Since the mid-1990s, attempts to improve and extend the modeling of climate change impacts on malaria transmission using the MIASMA model (see Chapter 2) have been intensive. The IPCC process has generated positive feedback and has stimulated the following developments in modeling climatic impacts on malaria transmission:

• replacement of a global “world standard mosquito” with 19 regionally dominant anopheline species and their associated temperature-sensitive parameter values,

• the modeling of regional changes in seasonal transmission patterns,

• the estimation of additional numbers of people at risk under alternative emissions scenarios (unconstrained and constrained), and

• the modeling of how alternative socioeconomic development scenarios would modulate the impact of climate change on potential malaria transmission.

The last development listed above highlights the tension between seeking clarity of scenario-based modeling, with minimum specified change in the future, and seeking to incorporate as many of the important, plausible, modulating influences as technically possible. The minimalist approach, in the tradition of classical experimental science, says, “If we hold constant everything else, how would a change in world climate affect malaria transmission?” The expansionist approach says, “Yes, but that is unrealistic. We live in a changing world—and, furthermore, we have the capacity to enact various purposeful changes that might reduce the incidence of malaria. So, the more i...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Preface
• Introduction
• PART 1. Malaria and Climate Change: Issues and Analytic Tools
• PART 2. Regional Assessments
• PART 3. A Changing Context
• PART 4. Synthesis
• Index
• About the Editors