Globalization and infectious disease
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SPECIAL TOPICS NO.3
Globalization and infectious diseases: A review of the linkages
TDR/STR/SEB/ST/04.2
The “Special Topics in Social, Economic and Behavioural (SEB) Research” series are peer-reviewed publications commissioned by the TDR Steering Committee for Social, Economic and Behavioural Research.
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Dr Johannes Sommerfeld Manager Steering Committee for Social, Economic and Behavioural Research (SEB) UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR) World Health Organization 20, Avenue Appia CH-1211 Geneva 27 Switzerland
E-mail: sommerfeldj@who.int
Globalization and infectious diseases: A review of the linkages
Lance Saker,1 MSc MRCP Kelley Lee,1 MPA, MA, D.Phil. Barbara Cannito,1 MSc Anna Gilmore,2 MBBS, DTM&H, MSc, MFPHM Diarmid Campbell-Lendrum,1 D.Phil.
1 Centre on Global Change and Health London School of Hygiene & Tropical Medicine Keppel Street, London WC1E 7HT, UK
2 European Centre on Health of Societies in Transition (ECOHOST) London School of Hygiene & Tropical Medicine Keppel Street, London WC1E 7HT, UK
TDR/STR/SEB/ST/04.2
TDR/STR/SEB/ST/04.2
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Acknowledgement The authors wish to thank colleagues at the Centre on Global Change and Health, London School of Hygiene and Tropical Medicine, for their helpful advice in the writing of this paper. We are particularly grateful to Professor David Bradley for his detailed comments and expertise in reviewing the final draft..
Design and layout: Lisa Schwarb
TABLE OF CONTENTS
LIST OF TABLES, FIGURES AND BOXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
ABBREVIATIONS AND ACRONYMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
- INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
- BACKGROUND 2.1 What is globalization? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Global burden of infectious disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
- GLOBALIZATION AND THE CHANGING NATURE OF INFECTIOUS DISEASE . . . . . . . . . . . 9
- ECONOMIC GLOBALIZATION AND INFECTIOUS DISEASE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.1 World Trade Organization and multilateral trade agreements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.2 The global trade in food . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.3 The global trade in pharmaceuticals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5 GLOBAL ENVIRONMENTAL CHANGE AND INFECTIOUS DISEASE . . . . . . . . . . . . . . . . . . . . . 17 5.1 Global climate change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.1 Global warming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.1.2 Global weather change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.1.3 Vulnerability to global climate changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.2 Water supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.2.1 Large dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.2.2 Small water projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 5.2.3 Displacements, disruptions, distant effects and migrations . . . . . . . . . . . . . . . . . . . . . . . 29
5.3 Deforestation and land clearance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.3.1 Deforestation, land clearance and “new” or “emerging” infections . . . . . . . . . . . . . . . 31 5.3.2 Vector-borne infections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.3.3 Pharmacological implications of loss of biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6 GLOBAL DEMOGRAPHIC CHANGE AND INFECTIOUS DISEASE 6.1 Globalization and population mobility
6.1.1 Trends in population mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 6.1.2 The causes of population mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 6.1.3 Population mobility and infectious disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2 Refugees and displaced persons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 6.3 Long-term migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.3.1 Migration to low-income countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 6.3.2 Migration to high-income countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.4 Urbanization 6.4.1 The growth in urban populations and the influence of globalization . . . . . . . . . . . . . . 39 6.4.2 Urbanization and infectious disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
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7 GLOBAL TECHNOLOGICAL CHANGE AND INFECTIOUS DISEASE . . . . . . . . . . . . . . . . . . . . . . 45 7.1 Information and communication technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 7.2 Transportation technologies: the growth in short-term travel . . . . . . . . . . . . . . . . . . . . . . . . . . 46
7.2.1 The growth in short-term travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 7.2.2 Short-term travel and infectious diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 7.2.3 Transport of goods and infectious diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
7.3 Medical technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
8 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Special Topics No. 3 • Globalization and infectious diseases: A review of the linkages v
BOXES
Box 1: Transmission of infectious diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Box 2: Infectious diseases and the natural environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Box 3: Preventing and treating human infections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Box 4: Projections of the health impacts of global environmental change . . . . . . . . . . . . . . . . . . 17
Box 5: The scientific evidence for global environmental change . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Box 6: Global climate change and vector-borne diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Box 7: Climate effects on vectorial capacity, basic reproductive number, vector abundance and distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Box 8: El Niño and infectious diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Box 9: Infection and water projects along the Nile river . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Box 10: Malaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Box 11: Dengue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Box 12: Infectious disease and the Haj . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
FIGURES
Figure 1: Alternative scenarios of future development and associated climate change
developed by the IPCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figure 2: Global average near-surface temperatures, 1860-1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 3: The global average temperature rise predicted from the unmitigated emissions scenario, and the emission scenario which stabilizes CO2 concentrations at 750 ppm and at 550 ppm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
LIST OF TABLES, BOXES AND FIGURES
ACL anthroponotic cutaneous leishmaniasis
AVL anthroponotic visceral leishmaniasis
CME WHO Commission on Macroeconomics and Health
DALY disability adjusted life year
DNA deoxyribonucleic acid
ENSO El Niño Southern Oscillation
EWE extreme weather events
FAO Food and Agriculture Organization
FDI foreign direct investment
GATS General Agreement on Trade in Services
GATT General Agreement on Tariffs and Trade
GBDS Global Burden of Disease Study
GDP gross domestic product
GIS geographical information system
HIV/AIDS human immunodeficiency virus/acquired immunity deficiency syndrome
ICT information and communication technologies
ID infectious diseases
IHA International Health Regulations
ILO International Labour Organization
IPCC Intergovernmental Panel on Climate Change
JBE Japanese B encephalitis
MDR-TB multidrug resistant tuberculosis
MTA multilateral trade agreement
NCD non-communicable disease
RVF Rift Valley fever
SAP structural adjustment programme
STD sexually transmitted disease
TB tuberculosis
TBT Agreement on Technical Barriers to Trade
TDR UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases
TNC transnational corporation
TRIPS Agreement on Trade Related Intellectual Property Rights
UNAIDS United Nations Joint Programme on HIV/AIDS
UNDP United Nations Development Programme
UNITeS United Nations Information Technology Service
WHO World Health Organization
WTO World Trade Organization
WTO World Tourism Organization
ZVL zoonotic visceral leishmaniasis
ABBREVIATIONS AND ACRONYMS
EXECUTIVE SUMMARY
Special Topics No. 3 • Globalization and infectious diseases: A review of the linkages 1
G lobalization is a complex and multi-faceted set of processes having diverse and widespreadimpacts on human societies worldwide. It can be defined as “changing the nature of humaninteraction across a wide range of spheres including the economic, political, social, technological and environmental…… the process of change can be described as globalizing in the sense that bound- aries of various kinds are becoming eroded. This erosion can be seen to be occurring along three dimen- sions: spatial, temporal and cognitive” (Lee, 2003).
Globalization is driven and constrained by a number of forces: Economic processes, technological developments, political influences, cultural and value systems, and social and natural environmental factors. These varied forces, as part of the processes of globalization, impact directly and indirectly on health at a number of different levels.
As globalization spreads across the world, there is much to be understood about how the wide-rang- ing changes are impacting on infectious diseases. This paper reviews the existing evidence about the links between globalization and infectious diseases in terms of changes in disease distribution, trans- mission rate and, in some cases, management of disease. The aims of the paper are to:
• improve understanding of how globalization influences infectious diseases, particularly in the devel- oping world;
• explore how the processes of globalization impact on the epidemiology of, risk factors for, and capacity to control, infectious diseases;
• examine how efforts to control infectious diseases need to take account of globalization processes.
Reviewing the evidence for the four spheres of change – economic, environmental, demographic, tech- nological – this paper explores the complex causal relationships that may be arising. It shows both positive and negative consequences for the infectious disease burden potentially arise from globaliza- tion:
• Globalization appears to be causing profound, sometimes unpredictable, changes in the ecological, biological and social conditions that shape the burden of infectious diseases in certain populations. There is accumulating evidence that changes in these conditions have led to alterations in the prevalence, spread, geographical range, and control of many infections, particularly those transmit- ted by vectors.
• Individuals and population groups show varying degrees of gains and losses from economic global- ization, and thus differential vulnerability to infectious diseases. Studies of globalization processes show increasingly that the processes of change impact on the lives of individuals and populations in many different ways. Crude assessments of globalization as “good” or “bad” are neither accurate nor useful to effective management of global change.
• Epidemiology in general, and disease surveillance in particular, offer useful analytical tools and methods for identifying and measuring transborder patterns of infectious disease arising as a con- sequence of globalization. Such approaches are needed in studying how globalization may be chang- ing the distribution of health and disease within and across countries and regions of the world.
• Attention to the linkages between globalization and infectious diseases so far shows a dispropor- tionate focus on selected acute and epidemic infections. While there are clearly real risks from such diseases, which pose obvious challenges to an effective response from public health systems both nationally and internationally, it is important to consider the wide range of infections potentially affected by globalization processes.
• Due to inequalities in capacity and access to disease surveillance and monitoring systems between the industrialized and developing world, there is a danger of underestimating the infectious disease
burden faced by poorer countries. There is a particular need to develop surveillance systems that can be used effectively in low-tech, developing world contexts in order that true impact can be accu- rately identified. It is also imperative to ensure that, when changes in disease patterns are detect- ed, the information is transmitted to those able to implement appropriate action.
• The impacts of globalization on infectious diseases described in this report support the need for appropriate forms of global governance on key issues to improve systems of prevention, control and treatment.
• There is need for enhanced training on the global dimensions of infectious diseases. Medical prac- titioners would benefit from a greater understanding of the potentially changing profile of infec- tious diseases as a result of increased population mobility, intensified trade in goods and services, climate change, and other factors linked to globalization.
• The findings of this report support the need to pay greater attention to the impacts on the infec- tious disease burden of policy decisions taken in other sectors e.g. trade and investment, large infra- structure projects (e.g. dam building), migration, agriculture, transportation, communications.
• It is clear that improving action regarding the impact of globalization on infectious diseases on an a priori basis is a highly cost-effective policy intervention. It is increasingly recognized that the long-term sustainability of globalization requires greater attention to the social (including health) costs of current forms of globalization. What needs to be understood more fully is that resources committed to infectious diseases prevention, treatment and control in a globalizing world is a worthwhile investment.
Globalization and infectious diseases: A review of the linkages • Special Topics No. 32
Special Topics No. 3 • Globalization and infectious diseases: A review of the linkages 3
1 INTRODUCTION
Although there is a flourishing literature on globalization and health,1 much remains to be understood about how the processes of globalization affect health outcomes, and consequently about what local and global public health responses are appropriate. One major focus of this literature has been the links between globalization and infectious disease. There are particular concerns that globalization is impacting on the epidemiology of infectious disease, and on the capacity to effectively prevent, con- trol and treat these diseases. It may, for example, influence the risk factors for specific diseases, and at the same time enhance the opportunities for improving surveillance, monitoring and reporting capacity through global information and communications technologies.
This paper reviews the current evidence for links between globalization and infectious disease. In par- ticular, it identifies changes in disease distribution, transmission rate, and in some cases, management of disease. The aims of the paper are to:
• improve understanding of how globalization influences infectious diseases, particularly in the devel- oping world;
• explore how the processes of globalization impact on the epidemiology of, risk factors for, and capacity to control, infectious diseases;
• examine how efforts to control infectious diseases need to take account of globalization processes.
The paper extensively reviews the relevant published English language literature and, where possible, literature in other languages. It also reviews a substantial amount of “grey” literature. The focus is on the priority diseases of the UNICEF/UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases (TDR).
1 For a review of the literature see: Lee K. Globalization and health policy: a review of the literature and proposed research and policy agenda. In: Bambas A et al., eds. Health and human development in the new global economy. Washington DC, Pan American Health Organization, 2000:15-41. Also see: Lee K. Globalization and health, an introduction. London, Palgrave Macmillan, 2003.
Special Topics No. 3 • Globalization and infectious diseases: A review of the linkages 5
2 BACKGROUND
2.1 What is globalization?
Despite widespread interest in its emergence and impact, there is limited agreement in the literature on precisely what globalization is. Frequently it is understood and defined according to selected aspects. Thus, for economists, globalization concerns the increasingly globalized nature of the emerg- ing world economy. For lawyers, it concerns the threatened changes in legal status of states and their citizens. For environmentalists, it is the changes in the world’s climate and other biosystems. And for information technology experts, it is the global spread and integration of information systems (Lee, 2003). However, such disciplinary-based perspectives can neglect the multiplicity of change processes, and hence fail to appreciate their complex direct and indirect impacts.
The numerous definitions of globalization in the literature also reflect a renaming of existing phenom- ena. In understanding the links between globalization and infectious disease, it is important to be aware of how the term ‘globalization‘ is used interchangeably with terms such as ‘internationalization’, ‘liberalization’, ‘universalization’ and ‘westernization’.2 A strict definition of globalization distinguishes between cross-border and transborder flows. ‘Cross-border’ concerns the interactions across two or more countries through, for example, the documented movement of people, official trade of goods and serv- ices, or capital flows such as foreign direct investment (FDI) across national borders. Cross-border flows have increased quantitatively since the end of the Second World War but can be more accurately described as internationalization. ‘Transborder’ or transnational, in contrast, concerns flows of people, goods and services, capital, values and ideas, and other entities in a way that does not recognize national borders. Such flows are ‘supraterritorial’ in the sense that they are disconnected from territo- rial geography. While intensified cross-border flows can overwhelm the capacity of the state to regulate them, transborder flows are seen as potentially eroding or even redefining existing territorial bound- aries separating human societies from one another (Scholte, 2000). Examples include global environ- mental change, undocumented population mobility (e.g. trafficking of people), and money laundering.
Along with changes to spatial boundaries, Lee (2003) argues that globalization is leading to changes in how we experience and perceive time. Globalization is shaping the timeframe in which natural and human-induced phenomena take place, as well as the time available and necessary for responding to these phenomena. For example, the time taken for some infectious diseases to spread across territorial space has become much quicker as a result of the increased amount, frequency, and speed of popula- tion mobility. Similarly, the potential capacity to detect and report disease outbreaks has quickened due to the advent of global information and communication systems.
Finally, in a variety of ways, globalization is influencing how we think about ourselves and the world around us. This cognitive dimension of global change arises from the proliferation of a range of indi- viduals and institutions with global reach, which are concerned with the production and exchange of knowledge, values and beliefs. They include the mass media, think tanks, research institutions, consul- tancy firms, advertising agencies, religious groups, educational institutions and policy-making organi- zations. While some argue that this is leading to the emergence of a ’global culture’ dominated by west- ern values and beliefs, others believe the spread of ideas and principles on human rights, labour stan- dards, and other social values across national or regional boundaries is a progressive force. Some writ- ers point to the flourishing of competing ideologies and value systems, resulting at times in a ’clash of civilizations’ in the form of religious or political conflict (Huntingdon, 2002).
2 For a useful discussion of the distinct meanings of these terms, see: Scholte JA. Globalization, a critical introduction. London, Palgrave Macmillan, 2000.
Globalization and infectious diseases: A review of the linkages • Special Topics No. 36
In summary, globalization is a complex and multi-faceted set of processes that are having diverse and widespread impacts on human societies worldwide. Globalization can be defined as a set of processes that are:
Changing the nature of human interaction across a wide range of spheres including the economic, politi- cal, social, technological and environmental. …the process of change can be described as globalising in the sense that boundaries of various kinds are becoming eroded. This erosion can be seen to be occurring along three dimensions: spatial, temporal and cognitive (Lee, 2003).
Overall, it is clear that globalization is driven and constrained by a number of forces: economic processes, technological developments, political influences, cultural and value systems, and social and natural environmental factors. These varied forces, as part of the processes of globalization, impact directly and indirectly on health at a number of different levels. For example, globalization can alter health status through changes in basic living conditions and household incomes. It can affect the availability of health workers and other resources in health care systems through changes in patterns of population mobility, impact on government health expenditure through changes in macroeconomic policy, and encourage the adoption and spread of health standards and principles through interna- tional and global agreements (Woodward et al., 2001). At different levels, therefore, global change can bring either health benefits or costs, depending on who you are and where you live. For poorer pop- ulations, there is substantial evidence to suggest that, so far, globalization has posed more negative than positive impacts on health, including risks from infectious disease.
2.2 Global burden of infectious disease
Historically, infectious diseases (IDs) have been the most important contributor to human morbidity and mortality until relatively recent times, when non-communicable diseases (NCDs) began to rival, and sometimes exceed, infections. Today, IDs still account for a large proportion of death and dis- ability worldwide and in certain regions remain the most important cause of ill health. The Global Burden of Disease Study (GBDS) estimates that, in the year 2000, infectious diseases were responsi- ble for 22% of all deaths and 27% of disability-adjusted life years (DALYs) worldwide (WHO, 2002). Although infectious diseases can affect people of all ages, they impose a particular burden on the young, notably on children under five. This is not only because younger age groups have a lower preva- lence of NCDs, but because they are more susceptible than adults to new infections, lacking the pro- tective mechanisms to reduce the impact of these illnesses. Consequently, in regions where a high pro- portion of the population is made up of young people – Africa, Latin America and many other devel- oping regions – infectious diseases usually extract a relatively high toll on the population. For exam- ple, GBDS estimates for 2002 were that infectious diseases were responsible for 52% and 50% respec- tively of all deaths and DALYs in sub-Saharan Africa but only 11% and 5% in the established market economies (WHO, 2000).
The term ‘infectious disease’ does not refer to a homogeneous set of illnesses but rather to a broad group of widely varying conditions. The relative and absolute importance of particular infections or groups of infections varies dramatically across regions. In high-income countries, deaths from IDs are overwhelmingly due to respiratory infections and HIV/AIDS. In sub-Saharan Africa, respiratory infec- tions, diarrhoeal diseases, HIV/AIDS, TB and malaria account for roughly similar proportions of total ID deaths (Murray and Lopez, 1997a). In addition, rates of specific infectious diseases are generally much higher in poor countries, regardless of the relative importance of these diseases. Therefore, in both relative and absolute terms, IDs are a considerably higher burden in low-income than high- income countries. An analysis of GBDS data concludes that the poorest 20% of the world’s population experiences a far higher burden of infectious disease compared to the remaining 80% of the world’s population (Gwatkin et al., 1999).
It should be noted that estimates of the burden of infectious disease at regional or global level can obscure the importance of specific infections in particular populations. For instance, tropical diseases impose a heavy burden on some of the poorest populations in the world but, since they occur almost exclusively in certain climates, can be recorded as making a proportionately small contribution to the overall infectious disease burden (Murray and Lopez, 1997a). Also, certain diseases such as dengue fever vary greatly with environmental and other determinants, and can rapidly assume epidemic proportions. This is often poorly represented in estimates of average annual disease incidence and prevalence. Finally, in most assessments, certain illnesses with a strong infectious component, such as liver cancer and several important neurological diseases, are not considered part of the infectious diseases burden (Satcher, 1995).
Estimates of the future burden of infections fall into two categories: predictions for individual diseases, and calculations of the overall impact of infectious diseases in the future. Examples of the former include those for HIV/AIDS and multidrug resistant tuberculosis, which often predict significant rises in prevalence and mortality (WHO, 1997; WHO, 2002). The most influential summation of the likely over- all future burden of infectious diseases predicts a gradual decline in both the rates of infection and their proportionate contributions to overall disease burden in all regions of the world (Murray and Lopez, 1996). However, these estimates assume that disease patterns will evolve in much the same way as they have in high-income countries over the past 100 or so years, and that current efforts to contain their impacts will be sustained. One finding from this review is that the future impact of many infections is uncertain because globalization is impacting on human societies and the natural environment in ways hitherto not experienced. Also, cases of certain infectious diseases (particularly vector-borne infec- tions) have either been rare or entirely absent in most high-income countries during the last 100 years (Murray and Lopez, 1996). Finally, shifts in political and economic values may lead to changes in cur- rent resources for infectious disease control, particularly in low and middle-income countries (Lee, 2003).
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3 GLOBALIZATION AND THE CHANGING NATURE OF INFECTIOUS DISEASE
The processes of globalization potentially influence a broad range of biological, environmental and social factors that affect the burden of many important human infections. This report considers the nature of infections and how, in simple terms, globalization may increase or decrease the distribution, spread and impact of infectious diseases in a given population.
An infection occurs when a micro-organism survives and multiplies within another, usually larger, organ- ism. The infected organism (e.g. human being) is called the host. In infectious diseases, unwanted signs and symptoms usually result from damage to the tissues and organs of the host, and the micro-organ- ism is known as a pathogen. A huge variety of pathogens cause human infections, ranging from sub- cellular viruses that cause lung infections in children to complex protozoan (e.g. the malaria parasite) and multicellular (e.g. filarial worms) organisms.
To trigger infection, pathogens must first reach the host., where they may survive unnoticed unless an internal or external event (for example, the herpes virus) triggers the disease. In most cases, pathogens reach the human host from the external environment through a variety of transmission systems (see examples in Box 1). The transmission system in operation determines which factors are capable of enhancing or inhibiting the spread of a particular infectious disease.
Box 1: Transmission of infectious diseases
Some pathogens live in the environment and are transmitted to humans directly, for instance, from the soil. Other pathogens can survive only in a host (an animal or human). If a pathogen survives in two (or more) animal species (e.g. humans and another type of animal) then the species within which the pathogen preferentially survives and multiplies is known as the pri- mary host; the other is known as the secondary or intermediate host. An intermediary agent (usually a biting insect or arthropod) that spreads a pathogen to humans is known as a vector, and an infection so transmitted is a vector-borne disease. Most TDR diseases are vector-borne infections. When pathogens spread directly from host to host, it is direct transmission. If direct transmission occurs between humans (or animals) the infection is contagious. Infections spreading between humans, without another animal reservoir host being involved (whether or not an intermediate host or vector is involved), are termed anthroponotic infections. When spread of an infection to a human or animal involves an intermediate host, it is indirect trans- mission. An infection that can be maintained in vertebrate animal populations, and is trans- missable between animals or from animals to humans, is known as a zoonotic infection. The mode of transmission influences which factors impact on the spread and overall impact of a specific infection. For instance, transmission of vector-borne diseases is influenced by factors which affect vector numbers (e.g. warmer temperature increases mosquito reproduction rates), contact between humans and vectors (e.g. tourism brings people to areas where malaria-carry- ing mosquitoes thrive), susceptibility of humans to vector-borne pathogens (e.g. migration of non-immune people to areas where malaria is prevalent), intermediate host numbers (e.g. dams provide breeding grounds for snails carrying schistosomiasis), or human or animal behaviour (e.g. warmer temperatures encourage people to bathe in pools, which may be contaminated by schistosome larvae).
A pathogen in a human host will only cause infectious disease if it is able to survive and multiply with- in the person. The success of this ‘amplification process’ is influenced by the presence or absence of many factors. For example, the person must be susceptible or non-immune to the infectious agent. People who are resistant to the pathogen are immune to the disease, typically as a result of a previous infection that has led to the production of protective antibodies or cells, or through immunization. There must also be sufficient numbers of pathogens present to overcome the body’s natural resistance to a foreign organism, and certain pathogens require physiological circumstances favourable to their multiplication; for instance, Clostridium perfringens infection usually requires the presence of dead or dying tissue.
Thus, amplification processes and transmission systems depend on multiple factors that determine not only whether a specific pathogen can survive and spread in the environment, but also whether an indi- vidual will become infected after the agent has reached this host, and whether the infection will cause disease (Jacob, 1998). These links can be appreciated through consideration of the ‘basic reproductive rate’ (or Ro) of an infectious agent, which refers to the average number of infections produced by a sin- gle case of the infectious disease in question. Where Ro is >1, the prevalence of the infection will increase, and where Ro is <1, it will decrease (Anderson and May,1991). Therefore, the effect of an eco- logical or other type of change on an infection can be considered by asking how this change will affect the Ro of the infectious agent.
Since, in general, the rate at which a single case of human infection produces new infections depends on a mixture of biological and social factors, transmission is affected not only by the population of infectious agents but also by the living conditions of the human population. Ro is affected by changes in, for example, the environment, and social and cultural practices, as well as by population size, age- distribution and density (May, 1994). Changes in the environment (Box 2) are particularly important to vector-borne infections since the proliferation and behaviour of vectors and (where appropriate) inter- mediate hosts are especially dependent on availability of the right conditions. Changes in all variables (economic, environmental, demographic), either individually or combined, may carry Ro from below to above unity (Ro = 1) or vice versa, thereby influencing the emergence, re-emergence or disappearance of specific infectious diseases. An understanding of the interactions between ecological factors and
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Box 2: Infectious diseases and the natural environment
Pathogens are highly sensitive to their environments. There are two main reasons for this: first, their ability to survive and multiply depends on the availability of the right climatic and nutri- tional conditions; second, to cause new infections, local conditions must facilitate a pathogen’s spread to a susceptible host. With human disease, this means that the environment must sup- port the survival of humans and, where necessary, the secondary host or vector, or contain an appropriate natural niche within which the free-living pathogen can flourish. There must be adequate means for humans to come into contact with the pathogen, either from other people or animals or the natural environment. Diverse environmental factors, such as ambient climate and the presence or absence of overcrowding, clean water or particular types of flora and fauna, influence a pathogen’s chances of flourishing and causing disease. Some pathogens thrive in warm and wet climates while others only survive in colder, drier conditions. Still others can sur- vive almost anywhere. Thus some pathogens cause disease worldwide while others are only found in well-defined areas where the local environment is favourable to their propagation. The latter is particularly true for vector-borne diseases since here the local environment needs to support the survival and multiplication of not only the offending pathogen but also the rele- vant vector and often a third host as well.
infectious diseases is therefore vital to predicting the future impact of infectious diseases and devel- oping appropriate measures for their control.
Appreciation of transmission systems and amplification processes also helps in understanding how infections can be prevented, controlled and treated. Interrupting the transmission of pathogens to sus- ceptible people will prevent infections, while eliminating or controlling a pathogen’s ability to survive and multiply in an established case will curtail the infection. Where treatment of an infectious case also renders that case non-infectious, it will also prevent further transmission. Box 3 lists some of the meth- ods available for preventing or treating infections.
In any situation, the appropriate preventive and treatment strategy depends on the particular pathogen or clinical disease to be controlled. Vector control is, for example, crucial to the prevention of vector- borne infections; the environment can be modified to deprive vectors of favourable breeding sites, or people may be advised to avoid areas where vectors flourish. Sometimes such modifications may enhance proliferation of one disease’s vector while inhibiting that of another’s, and therefore strategies must be appropriate not just in terms of their effect on a particular infection but also in terms of their effect on the whole infectious disease burden in a given area or population. In addition, for some dis- eases a quantitative or qualitative distinction is drawn between the measures required to control epi- demic versus endemic infections.3
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Box 3: Preventing and treating human infections
To prevent human infection, interrupt transmission of an infectious agent to humans by: • eliminating sites where pathogens, vectors, or intermediate hosts proliferate • reducing human exposure to pathogens or vectors through:
- regulating the natural and built environment and/or trade – using protective equipment (e.g. bednets to prevent malaria) – using chemoprophylaxis (e.g. antimalarial drugs to prevent malaria) – modifying behaviour (e.g. not engaging in unprotected sex to prevent HIV/AIDS) – isolating and treating infected cases (human or animal) to prevent them from spreading
the infection to others (e.g. identifying and treating TB cases as soon as possible to prevent transmission to others)
• increasing human immunity to pathogens through vaccination programmes.
To treat established infections, control multiplication of a pathogen in an infected person by: • administering chemotherapy to kill pathogens • using surgery or medical treatment to remove any continued source of infection, such as
an abscess • providing supportive treatment to enhance a person’s ability to destroy the pathogen
using his/her natural immunity to infectious agents.
3 For example, controlling epidemics of arthropod borne viral encephalitides might require intensification of measures that already play a part in controlling endemic disease. Thus vector control might be enhanced through fogging or spraying of suitable insecticides from airplanes and, in the case of Japanese B encephalitis, immunization of pigs might be considered. For typhoid fever or cholera, qualitatively different measures might be required to control an outbreak, e.g. chlorination of water supplies (Beneson AS, ed. Control of communicable diseases manual, 16th edition. Washington DC, American Public Health Association, 1995).
Globalization may profoundly influence many of the biological, social and environmental factors that impact on a pathogen’s potential to survive, spread and cause human disease. In addition, at both glob- al and local levels, the processes of globalization can influence the chances of successfully implement- ing measures to prevent, control and treat infections. Although good quality disease surveillance sys- tems can help detect changes in disease patterns, it is difficult to conclusively prove that globalization is itself responsible for changes in the spread or distribution of particular infections, or of infectious dis- eases in general. To prove that globalization is responsible for the increasing prevalence of a specific infection would require standardized monitoring of the exposure (the process of globalization being studied), the outcome (incidence of a particular infectious disease), and other determinants of disease (e.g. immunity, treatment, socioeconomic factors) over many years. The necessary studies would be extremely difficult to construct, and highly vulnerable to confounding due to new and unforeseen fac- tors developing out of the enormous transformations occurring in most aspects of contemporary politi- cal, economic and cultural life. In addition, surveillance systems describing the incidence and prevalence of infectious diseases over time are very rare, particularly for populations in developing countries, who are often the most likely to experience the adverse health effects of global transformations. Even if a causal association were detected, there would likely be considerable dispute over whether the relevant process, for instance global warming, was in fact caused by globalization.
Thus, the assessment of health risks associated with globalization must accommodate much unavoidable uncertainty. This does not mean that no conclusions should be drawn on the influence of global process- es on past, present and future disease levels. Indeed, poor or absent supportive evidence for the bene- fits of globalization has not dissuaded proponents of unregulated economic globalization from arguing forcefully for its introduction. The need to respond in situations where we do not have full and incon- trovertible evidence for our actions is well expressed by the precautionary principle: ’Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used for postpon- ing cost-effective measures.’4
Given the broad approach to globalization adopted by this paper (as described in Section 2.1), this review discusses four major aspects of globalization – economic, environmental, political and demo- graphic, and technological change. After a general discussion of each sphere of global change, consid- eration is given to how it may be influencing the distribution and spread of specific infectious diseases, and the severity of disease within certain population groups, in different parts of the world. This review focuses, in particular, on how the global change may impact on the distribution, spread, treatment and control of the TDR priority diseases. Admittedly, this subdivision is a simplification of a complex set of interrelated processes. For example, the links between global environmental change and infectious dis- ease cannot be seen independently from global economic change. Similarly, global economic change affecting the availability of resources for infectious disease control cannot be separated from shifts in political ideology shaping policy change at the national and global levels. These linkages are illustrated by the complex inter-relationships between the various aspects of globalization and malaria and dengue fever (see Boxes 10 and 12). For example the geographical reach and prevalence of malaria have been influenced by the economic, environmental, political and demographic aspects of globalization through economic adversity, increase in trade, spread of drug resistance, global warming, conflict, urbanization, and tourism, while technological advances have improved our understanding of the disease and should ultimately help improve its control. There have been various efforts to develop a conceptual framework to explain the linkages among these various spheres of change.5 Nonetheless, systematic assessment of each sphere provides a heuristic framework. It is a useful starting point to consider each sphere of glob- alization in terms of risk factors, epidemiology and transmission (including vectors), and control (includ- ing treatment and surveillance) of infectious disease. This also enables an examination of the positive and negative consequences of global change, and is a first step towards identifying key gaps in current knowledge.
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4 UN Conference on the Environment and Development, Rio de Janeiro, 1992 5 For example see Woodward D et al. Globalization and health: a framework for analysis and action. Bulletin of the World Health
Organization, 2001, 79:875-81; and Labonte R. Brief to the World Trade Organization: World Trade and Population Health. IUHPE Board of Trustees, 1999.
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6 For a detailed discussion see: Held D et al., Global transformations, politics, economics and culture. Stanford, Stanford University Press, 1999.
7 For a discussion of the public health implications of specific multilateral trade agreements see: WHO. WTO agreements and public health. Geneva, WHO/WTO, 2002.
4 ECONOMIC GLOBALIZATION AND INFECTIOUS DISEASE
Economic globalization describes the restructuring of the world economy, from one centred on produc- tion and exchange relations between economic entities located in different countries (international economy), towards “a highly complex, kaleidoscope structure involving the fragmentation of many pro- duction processes and their geographical relocation on a global scale in ways which slice through national boundaries” (Dicken, 1998). While this transition from an international to global economy has been a gradual one spanning many centuries, the processes of change have accelerated since the end of the Second World War and particularly since the early 1970s with major events such as the collapse of the gold standard, oil crises, and increased debt burden.6 These fundamental changes to economies worldwide are believed to be having a range of impacts on infectious diseases.
4.1 World Trade Organization and multilateral trade agreements
The emergence of the global economy has been facilitated, since 1945, by the significant growth of international trade, as well as of regional and international organizations that govern trade relations. Since the creation of the General Agreement on Tariffs and Trade (GATT) in 1944, member states have undertaken successive rounds of negotiations to reduce barriers to trade. In 1995, GATT was replaced by the World Trade Organization (WTO), a permanent body responsible for administering and enforcing a number of binding multilateral trade agreements (MTAs). These include the Agreement on Trade Related Intellectual Property Rights (TRIPS), General Agreement on Trade in Services (GATS), and Agreement on Technical Barriers to Trade (TBT).7
The economic impact of this proliferation in bilateral, regional and international trade agreements has been enormous. Since 1950, gross world production has increased five-fold while world trade has increased fourteen-fold (Lang, 2001). Marked changes were seen during the 1990s, when many coun- tries embarked on rapid economic reforms encompassing market liberalization, deregulation and priva- tization. Within a decade, populations living within market economies, or in countries engaged in mar- ket-oriented reforms, rose from one billion to roughly five and a half billion (Lehmann, 2001). A sub- stantial increase in all forms of international economic activity – FDI, capital markets, trade of goods and services, information and technology transfer – followed. As well as this internationalization of the world economy, there has been growing economic globalization in the form of restructuring of key sectors such as telecommunications, pharmaceuticals and food production.
There remains substantial debate about the precise impacts of trade on social welfare and, in particu- lar, on health. Proponents argue that trade is the “motor force” of the global economy and “human progress”, and that “more trade leads to more wealth, which in turn improves health” (Feachem, 2001). Others point to a more complex relationship, highlighting the need to ensure targeted protection of “human needs, social welfare, quality of life, indigenous understanding of knowledge and property” as well as to regulate goods and services that are harmful to health (Baris and McLeod, 2000; Lee, 2003). Although there is a strong relationship between increasing national wealth and overall health status, as income reaches US$ 5000 per capita, gains in health status and other economic factors, such as
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degree of income equality, become more important (Wilkinson, 1996). Furthermore, there is growing evidence that trade is leading to growing socioeconomic inequalities within and between countries (UNDP, 1999). While some writers continue to dispute the methodology behind such analyses (Ravallion, 1997), it is widely acknowledged that economic growth per se must be considered sepa- rately from the distribution of those benefits (Dikhanov and Ward, 2001). For many poor people, increased trade can lead to greater inequalities (Lunderg and Squire, 1999, as cited in Carpenter, 2000) that, in turn, have detrimental consequences for human health (Cornea, 2001; Goesling, 2001). The precise impact of MTAs on health, therefore, must be considered in relation to specific terms of trade and the resultant balance of winners and losers arising from them.
At a macroeconomic level, such changes can influence the overall level of resources available to gov- ernments for health expenditure. Rapid economic transition in central and eastern Europe during the 1990s, for example, was found to have undermined government capacity to provide for health care, and marked increases in the rates of several infections were reported (Maclehose et al., 2002). The Asian financial crisis in the late 1990s had a similar impact on public health spending. There is evidence to suggest that this, in turn, had detrimental effects on the rates of certain infections such as HIV/AIDS, tuberculosis and sexually transmitted diseases (STDs) (Sivaraman S, 1998). Reduced spending on vec- tor-borne disease control programmes in Africa during periods of structural adjustment has led to fail- ures to control diseases such as malaria, as well as to resurgence of some parasitic infections such as African trypanosomiasis (Sanders and Chopra, 2002). Furthermore, outbreaks of infectious diseases are themselves associated with significant costs in terms of lost trade and tourism revenue, and there is some evidence that fear of economic penalties has sometimes led authorities to under-report epi- demics, risking serious public health consequences. More comparative empirical analysis of the effects of trade liberalization on the epidemiology of infectious diseases is much needed.
Trade in specific products may have a more direct impact on infectious diseases. The most obvious examples are trade in food products and pharmaceuticals, and these are explored in more detail below. More esoteric examples also exist. For instance, the trade in used car tyres has led to the spread of dengue fever to cities, as examined below (section 6.4.2i). Economic change also leads to migration, and to alterations in land use and water requirements, which in turn have impacts on infectious dis- eases. This is also considered below.
4.2 The global trade in food
Consequences for infectious diseases arise from intensified trade in particular goods and services; this can be observed in the trends towards globalization of the food industry. Over recent decades, huge increases in international trade have transformed the availability of food products, particularly for inhabitants of high-income countries. This, in turn, has led to changes in dietary habits, and there is now a demand for year round availability of fresh fruit and vegetables, and for so-called “ethnic” foods. The convergence of tastes in many countries has meant greater demand for generic rather than local produce; cheaper transport systems of global reach now allow companies to manufacture many food products in less expensive labour markets, using ingredients from different parts of the world, and then to transport them worldwide.
The largest ten transnational corporations (TNCs) in the food industry are North American or European in ownership (Lang, 2001). Four companies control 90% of the world’s exports of coffee, tea, corn, wheat, pineapples and tobacco (Lee and Patel, 2002). In addition, large agrochemical TNCs are involved in the increasingly globalized food industry and account for 85% of the world market (Lang, 2001). Hence, a small number of large concerns now wield powerful control over the entire food chain, including agricultural production, processing and packaging, transporting and marketing (Lang, 1999). In 1994, the value of food trade was more than 300% greater than twenty years earlier (Kaferstein et al., 1997).
Although poor statistics make it difficult to estimate the global incidence of foodborne diseases, and there is substantial under-reporting, data from industrialized countries indicate that up to 10% of pop- ulations are affected annually by foodborne diseases (Kaferstein et al., 1997). Mass production, han- dling procedures, environmental factors, new and emerging pathogens, and poor regulation are believed to be contributing to a marked increase in worldwide incidence (Lang, 2001; Kaferstein et al., 1997; Swerdlow and Altekruse, 1998). Several factors may be responsible. First, the increasing reliance on producers abroad means that food may be contaminated during harvesting, storage, pro- cessing and transport, long before it reaches overseas markets. For example, outbreaks of Salmonella poona infection in the US associated with eating imported melons from Mexico have been linked to unhygienic irrigation and packaging practices at source farms. Low-income countries may also culti- vate non-indigenous crops to meet the needs of the export market, and these may be more suscepti- ble to indigenous pathogens. This happened when Guatemalan raspberries became contaminated with the protozoan Cyclospora, causing outbreaks of gastroenteritis in the US and Canada.
Second, centralized processing and mass distribution may lead to widespread dissemination of con- taminated foods. This risk has been augmented by changes in methods of food production such as the rearing of huge poultry flocks in communal housing, which practice generates large numbers of birds with common risk profiles. Similarly, outbreaks of E. coli O157:H7 have been traced to hamburgers from multiple outlets of a fastfood chain in the US, and clusters of gastroenteritis to flocks of Salmonella typhimurium infected poultry throughout Europe (Altekruse et al, 1997). Contaminated animal feeds may also be widely disseminated throughout the world, as exemplified by the bovine spongiform encephalopathy variant Creutzfeldt-Jakob disease (BSE/vCJD) crisis in the UK.
“New” pathogens not previously associated with human illness, such as Cyclospora and E. coli O157:H7, were first identified through epidemics of foodborne disease. Emerging zoonotic pathogens are becom- ing increasingly resistant to antimicrobial agents, largely because of widespread use of antibiotics in the animal reservoir. For example, Campylobacter isolated from human patients in Europe is now increasingly resistant to fluoroquinolone drugs, after these were introduced for use in animals (Endtz, 1991). Overall, there is a need to understand better how the global trade in food has spread hitherto local risks more widely, and has created new risks from increased economies of scale and changing methods of production.
4.3 The global trade in pharmaceuticals
In low and middle-income countries, pharmaceuticals account for about 30% of total health expendi- ture. The potential health benefits and risks posed by trade liberalization to access to pharmaceuticals are varied. Baris and McLeod (2000) argue that, as freer trade reduces tariffs on imported pharmaceu- ticals, drug imports will increase. In theory, countries will benefit from enhancing the range of drugs available, particularly where there is little or no domestic capacity to produce such products, and for- eign competition should exert pressure on prices overall. In practice, however, the effects on produc- tion and consumption are more complex given the changing structure of the pharmaceutical industry. Like the food industry, pharmaceuticals are increasingly dominated by a small number of large TNCs. In 1992, the top ten pharmaceutical companies were based in the US and Europe, accounting for about one-third of total combined sales worldwide (Baris and McLeod, 2000).
No low-income country appears in this super league (with the exception of China, which produces all of its essential drugs), but such countries do have the advantage of cheap labour and indigenous medicinal plants. Hence, there is a thriving generics industry in the developing world, and rapidly grow- ing international trade. However, increased access by large TNCs to markets in the developing world could undermine these local producers. Under the TRIPS agreement, domestic subsidies on drugs could be deemed an unfair trade advantage, and there may be a tightening of regulations around the pro- duction and trade of generic drugs.
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In relation to drug development, an emerging global market for pharmaceuticals raises concerns about a greater focus on conditions and markets deemed most profitable, regardless of the global burden of disease. How drugs will be developed for infectious diseases afflicting the poorest population groups within such a context remains unclear. For example, only 13 of the 1223 new chemical entities com- mercialized between 1975 and 1997 were for tropical diseases (Pecoul et al, 1999), and no new drugs for tuberculosis have been developed for over 30 years because, despite its enormous toll, only 5% of the 16 million infected can afford medication.8 These inequities contribute to the 10/90 gap in which 90 per cent of research funds address the health needs of 10 per cent of the world’s population (Global Forum for Health Research, 1999).
Finally, unregulated access to, and inappropriate consumption of, pharmaceuticals in a global market- place raises the issue of drug resistance. These factors have, for example, contributed to the spread of multidrug resistant tuberculosis (MDR-TB) worldwide, and will lead to further spread of resistance to antiretrovirals for HIV, particularly given the important role that the unregulated private sector plays in providing care for stigmatizing conditions (Brugha, 2003).9 Control of such diseases could therefore be jeopardized, and the misuse of pharmaceutical products facilitated, if sufficient regulatory mecha- nisms (including proscribed standards of use with adequate monitoring and enforcement) are not implemented alongside globalization of the pharmaceutical industry.
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8 Global Alliance for TB Drug Development, www.tballiance.org/2_3_C_NoRandDin30years.asp (accessed 27 August 2003).
9 As cited at www.tballiance.org/2_3_C_NoRandDin30years.asp.
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5 GLOBAL ENVIRONMENTAL CHANGE AND INFECTIOUS DISEASE
The environment consists of not only the natural world but also the built and social environments, and it plays an important role in shaping human health. The natural environment is modified by local influ- ences, such as local weather conditions, physical disasters or building developments, as well as global forces, such as changes in the great biophysical systems of the world that alter the global environment. Both local and global environmental change may be either natural or human-induced. Anthropogenic (human-induced) changes are increasingly linked to the processes of globalization (McMichael and Haines, 1997). Over the past 50 years, huge increases in economic and industrial activity have led to unprecedented effects on air, land and water environments, and the resulting changes have important and wide-ranging implications for human health, with different populations facing varying degrees of vulnerability to positive and negative impacts. This section explores the known and expected impacts on infectious diseases.
Box 4: Projections of the health impacts of global environmental change
Current knowledge can be used to make ‘best guesses’ of whether climate change is likely to have broadly positive or negative effects. Experts on the Intergovernmental Panel on Climate Change (IPCC) concluded that climate change is likely to expand the geographical distribution of several vector-borne diseases, including malaria, dengue and leishmaniasis, to higher alti- tudes (high confidence) and higher latitudes, assuming limited public health defences (medi- um/low confidence), and to extend transmission seasons in some locations (medium/high con- fidence). Climate change may decrease transmission of vector-borne diseases in some locations by reducing rainfall or raising temperatures to levels too high for transmission (medium/low confidence) (McMichael, 2001).
Quantitative statements about the impact of climate change on the burden of infectious dis- eases can be arrived at by coupling data from existing studies with estimates of expected glob- al climate change. For instance, data from the Peru diarrhoea study cited above can be applied to IPCC projections to make approximate estimates of how much the worldwide incidence of diarrhoea might increase with global warming (McMichael et al., 2003). More complex models have been used to investigate the possible effects of climate change on geographic distribu- tion of, and vectorial capacity in, vector-borne diseases. These either integrate climate effects on various components of the transmission cycle (e.g. Jetten and Focks, 1997; Martens et al., 1999), or simply make a statistical correlation between the current distribution of diseases and the most important climate variables (e.g. Hales et al., 2002; Rogers and Randolph, 2000).
Although these models should improve in the future, particularly as better quality health mon- itoring data become available, they will remain subject to major uncertainties, partly around the likely extent of future climate change but also around the relationships between climate and health outcomes, as other factors change. Socioeconomic factors, in particular, are often more important determinants of infectious disease burden, therefore global models based on climate alone are unlikely to give accurate predictions, particularly at the local level. Climate change will tend to increase risk over what would have been expected if no change had
5.1 Global climate change
Current concerns about global climate change can be divided into two main subjects: rising global aver- age land and sea surface temperatures (“global warming”), and increasing frequency of extreme weath- er conditions in many parts of the world. These are aetiologically linked, but since each is associated with different patterns of infectious disease, they will be discussed separately. In general, climate con- strains the range of infectious diseases, while weather affects the timing and intensity of outbreaks (Dobson and Carper, 1993).
5.1.1 Global warming
There is now substantial evidence that global average land and sea surface temperatures have increased by 0.6°C since the mid-nineteenth century. Most of this change has taken place since 1976, and 14 of the warmest years on record have occurred since 1980. In 1999, the UN Intergovernmental Panel on Climate Change (IPCC) predicted that average global temperatures would increase by 1.4-5.8°C by 2100.
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occurred, but socioeconomic development and control interventions could reduce both the existing (i.e. climate change independent) risk, and the vulnerability of populations to climate change. This is well illustrated in the context of diarrhoea. The provision of clean water and sanitation, combined with increased handwashing with soap, should not only cause very large reductions in diarrhoea rates, but by reducing the relative importance of water-borne and food- borne bacterial infections (which tend to respond positively to higher temperatures), compared to viral infections (which do not), the effects of climate change should become less important.
Fig. 1: Alternative scenarios of future development and associated climate change developed by the IPCC
Source: United Kingdom Climate Impacts Programme (UKCIP). Socio-economic scenarios for climate change impact assessment. A guide to their use in the UK Climate Impacts Programme. UKCIP, Oxford, 2000.
Globalization
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Special Topics No. 3 • Globalization and infectious diseases: A review of the linkages 19
A rise of this magnitude would be faster than anything encountered since the inception of agriculture around 10 000 years ago. Although the causes are controversial, IPCC has concluded that much of the warming observed in the last 50 years can be attributed to human activity (Albritton et al., 2001), prin- cipally due to excessive and inefficient combustion of fossil fuels, leading to the build up of greenhouse gases that trap heat within the atmosphere (McMichael, 1993). Patterns of precipitation have also changed: arid and semi-arid regions are becoming drier, while other areas, especially in mid-to-high lat- itudes, are becoming wetter, with a disproportionate increase in frequency of the heaviest precipitation events.
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Source: Climatic Research Unit, Norwich, UK.
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Global warming may alter the range and prevalence of many infections. As described in Box 5, higher ambient air temperatures, along with changes in precipitation and humidity, can affect the biology and ecology of disease vectors and intermediate hosts, the pathogens that they transmit, and consequent- ly the risk of transmission (Githeko et al., 2000). Diseases carried by mosquito vectors are particularly sensitive to meteorological conditions since these insects have fastidious temperature thresholds for survival and are especially susceptible to changes in average ambient temperature (Epstein, 2001a). Anopheles spp. mosquitoes can only transmit Plasmodium falciparum malaria parasites if the tempera- ture remains above 16°C, while the eggs, larvae and adults of Aedes aegypti mosquitoes that spread dengue fever and yellow fever are killed by temperatures below 10°C (Martens et al., 1997). Furthermore, within their survival range, warmth accelerates the biting rate of mosquitoes, and the mat- uration of parasites and viruses within them (McArthur, 1972), and, since insects have short lifespans, this increases the chances of their having two crucial blood meals – one from an infected person and the second for transmission of the pathogen to another person. The life cycle of the malaria parasite or other pathogen carried by the vector is thus accelerated. The precise effect on transmission requires continued study to determine whether shorter, more intense, lifespans lower or increase transmission, on balance.
Globalization and infectious diseases: A review of the linkages • Special Topics No. 320
Fig. 3: The global average temperature rise predicted from the unmitigated emissions scenario (red), and the emission
scenario which stabilizes CO2 concentrations at 750 ppm (blue) and at 550 ppm (green).
Source: Hadley Centre. Climate change and its impacts: stabilisation of CO2 in the atmosphere 1999. Hadley Centre, UK, 1999.
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