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ANÁLISE / ANALYSIS

New Approaches to Disease Control in the Context of Sustainable Development' Novas Abordagens ao Controle de Vetores de Doenças no Contexto do Desenvolvimento Sustentável

2 Robert Bos

BOS, R. New Approaches to Disease Vector Control in the Context of Sustainable Development. Cad. Saúde Públ., Rio de Janeiro, 8 (3): 240-248, jul/set, 1992. Faced with problems that are specific to the health sector and ones associated with issues of sustainability, programmes for the control of vector-borne diseases are increasingly resorting to environmental management measures to reduce populations of disease vectors as pan of an integrated control approach. The broader problems on the interface between environment and development that need to be addressed in the context of vector control include accelerated development of natural resources, demographic changes in rural populations and rapid urbanization. Disease vectors need to be recognized as biological risk factors to human health in the environment, and for a sustainable implementation of vector control measures, these should be made an integral pan of the development process. This requires modifications in the policy framework, expansion of our knowledge base, development of operational methods and techniques and a shift in emphasis in training and education. Keywords: Vector-Borne Diseases; Environment; Development Policies; Sustainable Development

INTRODUCTION control with the advent of affordable residual in the 1940s and 1950s. By the Since the beginning of this century the middle of the 1970s, however, the problems control of disease vectors has been an that inevitably arose from the almost important component of strategies in the fight exclusive reliance on house spraying against vector-borne diseases. There has been campaigns and urban larviciding led to a re- an evolution in the nature of the control consideration of the existing options, and to methods over time as epidemiological fresh thinking about the development of new situations changed, new control technologies methods and tools. The 1980s witnessed a developed and new constraints arose. The move away from the universal application of focus on source reduction and species insecticides towards more balanced, integrated in the first half of the century control efforts with increased emphasis on shifted dramatically to chemical methods of methods of environmental modification and manipulation and personal protection adapted

1 to site-specific epidemiological and ecological The opinions expressed in this paper are the author's conditions. only and do not necessarily reflect the policies of the Vector-borne diseases not only continue to World Health Organization or of the other three UN be an important problem in agencies2 participating in PEEM. Community Water Supply and Sanitation Unit, and many countries in the tropical and sub- Secretary, joint WHO/FAO/UNEP/UNCHS Panel of tropical zones, but several of them are Experts on Environmental Management for Vector spreading and in many endemic areas their Control PEEM Secretariat, World Health Organization, transmission is intensifying. Global figures 1211 Geneva 27, Switzerland. show at least a stagnation in the success of efforts to control them, but in many parts of 1970s in South East Asia and East Africa, has the world there is gross under-reporting of subsequently spread to other parts of the disease incidence and the estimates are not world and has been followed by the reliable. The situation illustrates this development of resistance to other anti- point. An estimated two billion people are malaria drugs. On the long term this estimated to be at risk; some 270 million are development undermines the potential estimated to actually carry the parasite at any contribution of chemotherapy to the control of one time; annually, an estimated 110 million the disease. clinical cases result from infection; and estimates of annual mortality rates fluctuate • Resource Constraints on Intervention between 1 and 2 million (WHO, 1991). Programmes — Apart from the above Considering that some 80% of the malaria mentioned problems in malaria control, cases occur in sub-Saharan Africa, where resource constraints in the prevention and health authorities lack the resources to mount control activities aimed at other diseases effective control programmes, let alone carry underscore the continued need for vector out reliable epidemiological monitoring, such control efforts. In the case of schistosomiasis estimates have to be taken with a lot of an effective, single dose drug is available, but reservations. its cost has, until now, hampered its The problems faced by vector-borne disease widespread use in mass chemotherapy. Where control programmes today can for the purpose it has been used, such as in the long-term of this Conference be divided into health trials in selected villages on the island of sector specific constraints and problems Leyte in the Philippines, it has been shown arising from global trends on the interface that prevalence rates drop to a level that is between socio-economic development and the apparently determined by local environmental environment. and behavioural determinants of transmission (Olveda, in prep.). Sooner or later, managers of control programmes will be faced with the PROBLEMS CONFINED TO THE dilemma whether to proceed with expensive HEALTH SECTOR mass chemotherapy to treat a relatively small group of infected people or to instate a The health sector specific problems are of a probably equally expensive case detection technical, economic and managerial nature. system to target drug treatment on infected They include: people only. It is now increasingly recognized that other control methods, including snail • The Development of Resistance control and improved sanitation, will continue — While resistance to DDT was detected in to be needed. Another example is Japanese anopheline vectors in Greece as early as the encephalitis, an arboviral disease associated 1950s, there was a strong belief at the time with irrigated rice ecosystems in South and that malaria eradication using residual house South-East Asia. While a vaccine for this spraying could be achieved before this infection is available, its price (US$10/dose) phenomenon would develop into a problem of and the cost of an effective delivery system serious proportions. However, things took a impede its use in many endemic countries. different turn and control programmes had to Again, vector monitoring and control need to seek resort in the application of increasingly be relied on to prevent major outbreaks. expensive alternative compounds, which reduced their economic viability before the • De-emphasis on Vector Control as a Result final goals could be met. of Integration — In many countries the health sector has been re-organized based on the • The Development and Spread of Drug recommendations adopted unanimously by the Resistance — Resistance of the malaria WHO Member States at the International parasite to chloroquine, first discovered in the Conference on Primary Health Care in Alma Ata in 1977. These changes include a shift Resources — The continuously rising demand from vertical, single disease oriented for food, fibre and energy forces national programmes to horizontal programmes. As a authorities to rapidly develop land and water result, in many countries the activities of resources for agricultural production and malaria control campaigns and other vector- energy generation. Irrigation schemes and borne disease control programmes have been man-made reservoirs may provide new integrated into the general health services. habitats for disease vectors. The adverse This change was dictated by the economic environmental consequences of this type of realities since the 1970s and supported by development include deforestation, soil considerations of social justice and equity. In erosion and degradation, desertification and many countries, however, the vector control waterlogging. Each of these may also affect component of control activities has been the ecology of local vectors and lead to a reduced disproportionately, to the extent that deterioration of the vector-borne disease the question has been raised whether vector situation. As far as the human health control should remain the responsibility of the dimension of these problems is concerned, it ministry of health. In some countries can be attributed, in general terms, to (Singapore is a success story in this respect, insufficient intersectoral consultation at the see Chan Kai Lok and Bos, 1987) vector early planning stages, inadequate health risk control has moved to become a responsibility assessment at the time of feasibility studies of the ministry of the environment. The loss and the failure to incorporate environmental of profile of vector control has contributed in health safeguards as part of the project during an important way to current human resource the construction phase. In the end, the health constraints, as professional career perspectives sector is faced with intensified health in this area of speciality have lost a great deal problems but in its already stretched budget of attraction. there is usually no room to meet the needs in The above problems are, by and large, a terms of strengthening of health services, matter for the health sector to solve; policy modifications linked to programmatic • Demographic Changes in the Rural Areas — changes, a reformulation of research goals Development of natural resources often results and a redefinition of training objectives are in considerable changes in the density, required. composition, settlement conditions and movement of human populations. Resettlement prior to the filling of reservoirs, or as part of agricultural development may VECTOR-BORNE DISEASE PROBLEMS introduce non-immunes or parasite carriers AND GLOBAL into new risk areas. Agricultural development ENVIRONMENT/DEVELOPMENT may also create new migration patterns of ISSUES people attracted by the economic opportunities created or of seasonal labourers in relation to A number of global trends on the interface the cropping cycle. These demographic between environment and development have changes have the potential to promote the immediate repercussions for the vector-borne spread of vector-borne diseases, as disease situation and for the effective exemplified by the spread of schistosomiasis implementation of vector control operations. in the middle Awash Valley in Ethiopia The most important of these trends is, beyond (Meskal, 1987). They may also exacerbate the doubt, the continued growth of the human specific health sector problems, as for population, expected to reach 6 billion before example in the case of Thailand, where the year 2000. This has a range of migration has contributed to the spread of consequences, each with its own impact on chloroquine resistant malaria. vector ecology, and include: • Rapid Urbanization — Attracted by the • Accelerated Development of Natural economic opportunities of the big city, the movement of rural people to urban centres of true both for agricultural pests and vectors of the developed countries was an important diseases. The situation may be further phenomenon of the 1960s and 1970s. While it exacerbated by the excessive use of continues to make an important contribution pesticides. In particular their use for to urbanization, by the middle of the 1980s it agricultural purposes which makes up the was substituted by the intrinsic growth of greatest part (90%) of pesticide applications urban populations as the first cause of rapid and moreover releases residues in the urban expansion. As the municipal authorities environment in an indiscriminate manner, cannot keep pace in terms of basic services of affects populations of natural enemies of pest drinking water supply, sanitation and solid species and leads to the accelerated waste collection, environmental degradation in development of insecticide resistance. the big cities inevitably results in increased risks of certain vector-borne diseases: dengue, lymphatic filariasis and, in some cases, VECTOR CONTROL IN THE CONTEXT malaria. On the basis of trends in urbanization OF SUSTAINABLE DEVELOPMENT it can be predicted that urban vector control will require a major increase in resources in While the term "sustainable development" the next couple of decades. was not in first used by the World For the adoption of Agenda 21 the UNCED Commission on Environment and will address a number of global Development (WCED, 1987), it deserves environmental issues, such as global climatic credit for the clear definition of the concept, change, ozone-layer depletion, reduction of for the review of how the current range of biodiversity, desertification and the global and local environmental problems is a of the oceans and seas. At least two of these result of on the one hand unchecked industrial issues have plausible vector ecological development and on the other hand implications. Global climatic change may unacceptable inequity and associated poverty, modify the distribution of vector-borne and for formulating proposals for reforms in diseases and the dynamics of vector policies and institutional arrangements that populations. A rise in mean temperatures may will contribute to an improvement of the push the limits of, for instance, malaria situation. In its report "Our Common Future", transmission to higher latitudes and altitudes. the Commission defines sustainable Changed rainfall patterns may affect the development as development that aims at seasonality and distribution of transmission. meeting the needs of the present generation Changed wind patterns and intensities may without compromising the ability of future contribute to the passive migration of generations to meet their own needs. It vectors. As models for climatic change are cautions that further development should still relatively speculative (apart from a global ensure a minimal depletion and destruction of rise in temperatures) and cannot predict the Earth's resource base and should aim at changes in local conditions, very little can be reducing poverty which is at the root of major said with certainty about its effect on vector- environmental degradation. borne disease transmission. Possible effects In putting the control of disease vectors in are presented in Table 1 (WHO, 1990). the context of sustainable development, two Monitoring of malaria transmission in points have to be clarified. First of all the sensitive areas (at the altitude limits of human health dimension of environmental transmission) will assist in confirming the problems needs to be better defined. This expected change. goes beyond vector-borne diseases: there are A reduction in biodiversity may also affect numerous physical and chemical risk factors the vector-borne disease situation. Resource to human health in the environment. development projects invariably lead to Disease vectors are, however, unique in that habitat simplification, and often favour pest they are biological risk factors and therefore species over their natural enemies. This is capable of adapting to new conditions. This adds to the complexity of the problems they • Modifications in the policy framework; cause. Secondly, the conditions required to • Expansion of our knowledge base; operationalize sustainable development • Development of operational methods and principles and approaches in the planning and techniques; implementation of vector control need to be • A shift in emphasis in training and outlined. This will be discussed in the education. remainder of this paper. As can be concluded from the Brundtland Policy Matters report, the potential of sustainable development comes to expression in a The decision-making processes leading up multidisciplinary understanding of the key to development project are guided by problems, and the political will to make an government policies and, whenever external intersectoral move towards lasting solutions. support is required, by policies of bilateral For vector control this means that the and multilateral development agencies. question is whether, instead of protecting Government policies are hierarchically communities from vector-borne disease risks structured. Macro-economic policies at the in the traditional, sectoral manner once we are national level are translated into sectoral faced with the consequences of development, policies as the basis for programmes of we can install permanent conditions as a part individual ministries. A recent literature of development to reduce vector-borne disease review by WHO and the World Bank of the hazards to an absolute minimum and with the health impact of development policies least possible pressure on the Earth's (Cooper-Weil et al., 1991) revealed a range of resources. inadvertent consequences on the human health These views were recently re-inforced by status of agricultural, industrial, energy and the WHO Commission on Health and housing policies. The cause-and-effect Environment. In its report "Our planet, our relationship between macro-economic policies, health" (WHO, 1992) it extends the sectoral policies and the human health status relationship between development and the is also raised by the WHO Commission on environment with the explicit repercussions Health and Environment (WHO, 1992). In for the human health status. Under the many cases the linking factors are heading Food and Agriculture the environmental determinants of health. In 1989 Commission recommended, inter alia, that the WHO/FAO/UNEP Panel of Experts on more research should be carried out on how Environmental Management for Vector to increase food production in the tropics Control (PEEM) carried out a similar policy while reducing tropical diseases and harmful review in the narrower context of the effects effects on the environment and in a separate of water resources development on vector- section on water issues it stressed that the borne disease transmission (Mather and Bos, priority for control in the 1989). Policies involved may be as diverse as world is the control of bacteriological and guidelines for equitable distribution of water parasitic water-borne diseases. in irrigation schemes or the use of the Internal Rate of Return as the major criterion at the appraisal phase of development projects. At AREAS IN WHICH THE the same time, health sector policies may not NEW APPROACH SHOULD be conducive to the establishment of an TAKE EFFECT intersectoral dialogue and impede optimal participation of health sector staff in Four areas can be distinguished where new intersectoral efforts of problem solving. initiatives may contribute to the incorporation of principles of sustainable development in Insufficient Knowledge Base vector control: The emphasis on chemical methods of vector control after the Second World War is the project. Monitoring and surveillance reflected in the research priorities during during the construction phase should confirm those decades and continues to be felt. As a the initial forecast and detect any unexpected result, there is a bias towards information on health effects requiring interventions. The issues such as vectorial behaviour with development of remote sensing techniques relevance to indoor wall spraying campaigns and the use of geo-referenced databases will (exophily/exophagy versus be of strong support to overall monitoring. endophily/endophagy), genetic mechanisms of insecticide resistance or the relative Re-Direction of Training and Education effectiveness of different types of insecticide application. At the same time, there has been Tertiary education is aimed at the formation a dearth of studies on vector ecology and of professionals in sharply defined disciplines. particularly on the nature of the association As a result communication between between land and water resources professionals of different disciplines is often development, environmental change and difficult. They have been trained neither to vector population dynamics. This is true as appreciate the opportunities that are available well for the epidemiological dimension of in other disciplines, nor to understand the environmental approaches to vector control: constraints faced by professionals in other there is a great need to better define under fields. A re-direction of training does not which conditions a reduction in population imply making a vector specialist out of an densities will be effective or not. A new engineer or vice versa, but it should help to attitude is required: rather than thinking in develop the capacity of professionals to work terms of a universally applicable method, in multidisciplinary teams in a problem- researchers have to start thinking in terms of oriented approach. Rather than expanding characterization of local eco-epidemiological detailed knowledge of individual experts situations and design "custom-made" beyond their area of speciality, professionals environmental interventions for each specific should know where to go to obtain available case. information when it is needed. This requires changes in University course curricula and the Inadequate Operational Methods and introduction of problem-based learning Techniques techniques. Community education should also become In order to be able to participate in the more intersectoral. Specific health subjects are planning of development projects and in the usually effectively disseminated to the design of health safeguards that are an community level by the traditional health integral part of such developments, vector education systems. However, it is unlikely specialists need new methods and techniques. that a farmer will accept directives on Environmental Impact Assessment is now part changes in agricultural practices which are to of most feasibility studies, and health risk contribute to improved assessment should be integrated into this. conditions if they come from a health Health sector professionals must be ready to educator. Alternative and more appropriate work with engineers in rapid appraisal vehicles for such messages need to be used, exercises. A methodology for such an such as, in the case of the above example, appraisal is proposed in guidelines that have agricultural extension programmes. Efforts to been produced by the WHO/FAO/UNEP promote this intersectoral approach in PEEM (Birley, 1989). Once the risks are community education are underway and will identified, options for health safeguards, soon be tested in a number of countries. monitoring and surveillance and control have to be analyzed for their cost-effectiveness. The results of this analysis have to be RECOMMENDATIONS presented at the time of economic appraisal of Based on the above, a number of additional recommendations are recommended for RESUMO incorporation into the document under preparation at the Conference, under the BOS, R. Novas Abordagens ao Controle de general heading of intersectoral collaboration: Vetores de Doenças no Contexto do Desenvolvimento Sustentável. Cad. Saúde • Policies of the ministries involved in natural Públ., Rio de Janeiro, 8 (3): 240-248, jul/set, resources development (agriculture, energy, 1992. water resources etc.) should be reviewed for Devido a problemas específicos do setor their possible effect on the environmental saúde, bem como a problemas associados a determinants of human health and where questões de manutenção, os programas para o necessary adjustments should be negotiated; controle de doenças transmitidas por vetores estão cada vez mais retornando à adoção de • Planning procedures of new resource práticas de manejo ambiental para reduzirem development projects should include early, populações de vetores, como parte de uma intersectoral consultation as well as an abordagem de controle integrada. Os environmental impact assessment that includes problemas mais gerais advindos da interface a human health component beyond the strict entre ambiente e desenvolvimento que health sectoral interests; resources should be necessitam ser abordados no contexto do allocated to ensure the incorporation of the controle de vetores incluem a acelerada most cost-effective health safeguards into the exploração de recursos naturais, mudanças project design and implementation; demográficas em populações rurais e a rápida urbanização. Os vetores de doenças devem ser • Multidisciplinary research on disease vectors reconhecidos como fatores biológicos de risco and vector-borne disease should no ambiente para a saúde humana. Para uma be promoted as a joint endeavour of health, implementação sustentável das medidas de agricultural and environmental research controle de vetores, estes aspectos devem institutions; fazer parte do processo de desenvolvimento. Isto requer modificações na formulação de • In the course curricula of professionals in políticas, aumento da nossa base de health sciences and those who will work in conhecimento acerca destes processos, development projects, awareness creation of desenvolvimento de métodos e técnicas environmental health problems and training in operacionais, assim como uma maior ênfase multidisciplinary, problem oriented team work em treinamento e educação. should be included; Palavras-Chave: Vetores; Ambiente; Políticas de Desenvolvimento; • Alternative, potentially more effective Desenvolvimento Sustentável vehicles for community education on environmental management measures for vector control, such as the agricultural REFERENCES extension system, should be tested and employed. BIRLEY, M. H., 1989. Guidelines for the forecasting of vector-borne disease implications of water

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