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Priority setting and the ‘neglected’ tropical diseases
Transactions of the Royal Society of Tropical Medicine and Hygiene (2006) 100, 499—504
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LEADING ARTICLE
Priority setting and the ‘neglected’ tropical diseases David Canning Available online 15 March 2006
Summary In this paper David Canning argues that interventions against ‘neglected’ tropical diseases should be thought of as investments in human capital and form an integral part of global poverty reduction. He argues that overall burden of disease should not be the criterion for priority setting; if the goal is to maximize health benefits from a fixed health budget then cost-effective interventions should be prioritized. Whilst many people find objectionable the assignment of a monetary value to health, a cost—benefit approach, combining health and economic benefits, would allow the health sector to present arguments to policy makers, based on the rate of return on investment. Since many health interventions in low-income countries have exceptionally high rankings in terms of cost—benefit ratios, this should result in large flows from other sectors to the health sector. © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Many experts in the tropical ‘neglected diseases’ fear that that these illnesses are being downgraded when it comes to priority setting by the international community. While the Global Fund to fight AIDS, Tuberculosis and Malaria and the Global Alliance for Vaccination and Immunization (GAVI) have been successful in generating funding for their specific causes, the treatment and prevention efforts for other tropical diseases, such as lymphatic filariasis, leishmaniasis, schistosomiasis, trypanosomiasis, onchocerciasis, Chagas disease and the intestinal nematode infections (hookworm disease, trichuriasis and ascariasis), have been less successful at attracting attention and gaining international resources (Hotez et al., 2006). Is the relative position of the ‘neglected diseases’ in priority setting justified? Before answering this question we must first decide on what criteria to use for priority setting; this raises some important issues. The first is that the whole notion of disease priorities presupposes an emphasis on vertical, disease-specific interventions rather than broadbased health care services. Some activities — population
surveillance, treatment and vector control — may require specialized staff and a vertical approach. Even within a broad health care system, there has to be priority setting, and in the poorest developing countries, where health systems function very poorly, timely interventions may require a vertical approach rather than an effort at overall health system expansion and reform. The second issue is the need to emphasize judging priorities by evaluating outcomes. A different approach to priority setting is to emphasize the need for a fair and reasonable decision making process: for example, communities and disease victims should have an input into priority setting and a forum for making their views heard. The third issue is that priority setting in global health is often set up as the question of how best to spend some limited amount of resources. However, a large part of the question is how to generate increased support for health in the poorest countries of the world from more developed countries. While ‘best use’ of the resources may itself be attractive to donors, it is important to recognize that international donors may have other interests, over and above generating health. There are three areas in which this dif-
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500 ference in interests is important. The first is for infectious diseases that threaten developed countries. The second is when a disease is present in both developed and developing countries in a way that creates a common bond between sufferers. The high priority given to SARS and HIV/AIDS is in part due to these effects. The third is that wellbeing extends beyond health, and the international community has made poverty reduction a major goal, so that priority setting within the health sector has to take account of how it meets the goal of poverty reduction as well as improving health. This third issue is, of course, not one just for international donors, for even within a country an argument that health interventions reduce poverty is a powerful incentive to increase the health budget. It is difficult to argue for prioritizing most ‘neglected’ tropical diseases on the grounds that they spread to the developed world or to appeal to a community of sufferers in developed countries. However, as we shall see, there is a strong argument for some of the ‘neglected’ tropical diseases that investments in their control can be viewed as much as economic investments in human capital and worker productivity as health interventions and can be justified on those grounds. First we turn to the usual arguments for priority setting to improve health, given a fixed budget, and evaluate how the ‘neglected diseases’ perform on each criterion. We first consider the burden of disease. On this criterion the ‘neglected diseases’ fare badly since the bulk of the burden of infectious disease in developing countries comes from AIDS, tuberculosis and malaria, though recent research suggests that the morbidity burden of some neglected diseases may have been underestimated (King et al., 2005). The second is cost-effectiveness; on this criterion, some of the ‘neglected diseases’ do very well, with very cheap and effective cures and preventive measures being available. The third criterion is the moral imperative of the ‘rule of rescue’, the idea that we should prioritize diseases that pose an imminent threat to life; on this criterion, the most ‘neglected diseases’ do badly, since they are often chronic, but not life-threatening, conditions. We argue that it is difficult to justify the burden of disease, or the rule of rescue, as reasonable criteria for priority setting. If we accept we are trying to maximize the health produced, or death and disability avoided, we are led to prioritize interventions according to their cost-effectiveness. A number of the ‘neglected’ tropical diseases, notably onchocerciasis, filariasis and the intestinal nematode infections, have highly cost-effective interventions which are based on annual oral administration of drugs to the whole population in endemic areas and should be high priorities in terms of improving population health. In addition, to these population-based interventions, more targeted preventive interventions on groups with high prevalence rates, particularly infants and schoolchildren, can be used to prevent helminthic infections, schistosomiasis and blinding trachoma. These interventions also promise large economic payoffs, indeed they could be justified purely as economic interventions to increase educational outcomes and worker productivity, even in the absence of the health benefits. Thinking of these interventions as investments in human capital as part of a poverty reduction programme, as well
Leading Article as part of a health programme, would make them more attractive to policy makers outside the heath sector. This requires moving from cost-effectiveness estimates (the cost per unit of health outcome) to research that estimates the rate of return to these interventions as human capital investments (the discounted flow of increased earnings relative to the cost) to allow comparison with other human capital investments, such as education, thereby facilitating priority setting across sectors. While priority setting in terms of individual diseases may be justified, interventions that combine the treatment of several diseases in a common delivery method are likely to be more cost-effective. A good example is the GAVI initiative that targets a variety of diseases that can be prevented by vaccination. Grouping tropical and infectious diseases by treatment, for example, school-based or population-based annual mass drug distribution, or bednet use, and delivering treatments simultaneously, or using the same health sector infrastructure, is likely to produce a more attractive ‘packaged’ intervention than targeting each disease separately. Tackling the diseases outlined above, through populationor school-based drug administration, may be so cheap and have such large health and economic benefits that, as advocated by Molyneux (2004) and Molyneux et al. (2005), they should be a high priority even in the poorest countries. However, not all ‘neglected diseases’ are alike. For some, such as Chagas disease, dengue and leishmaniasis, vector control is the best hope for reducing the disease burden, but vector control is difficult and requires substantial expertise and commitment. Even in the case of malaria, treatment and vector control has proved difficult despite substantial resources being committed (Attaran, 2004). For others such as Buruli ulcer, early detection and treatment are the best course since treatment in the later stages, often involving surgery when the symptoms of the disease have become evident, is less beneficial and is expensive. However, early detection requires the correct diagnosis when symptoms are not obvious, and this requires a high standard of primary health care to be available. On cost-effectiveness grounds, and as economic investments, these should only be undertaken once other, more cost-effective interventions have been exhausted.
2. Priority setting for health One tool used for priority setting is the burden of disease. Taking death due to a disease, or some measure that incorporates morbidity as well as mortality, such as quality adjusted life years (QALYs) or disability adjusted life years (DALYs) gives an estimate of the total costs in terms of health loss imposed by a disease. Global burden of disease data for 2002, from the World Health Report (WHO, 2004), show that in Africa around 52% of the disease burden comes from infectious diseases. However, the DALY burden due to the ‘neglected’ tropical diseases and the worm infections is estimated to be only 4% of the total due to infectious disease: HIV/AIDS; malaria; the diarrhoeal diseases, such as cholera and rotavirus that are usually associated with lack of clean water and sanitation; the childhood cluster of disease, such as measles; and tuberculosis make up the vast majority of the burden.
Priority setting and the ‘neglected’ tropical diseases One response to this low disease burden is that is it based on mis-estimation. We can contrast the low estimate of the disease burden with the high prevalence rates for schistosomiasis and worm diseases in sub-Saharan Africa (De Silva et al., 2003): between 24% and 29% of the population are infected with each of trichuriasis, ascariasis, hookworm and schistosomiasis. The explanation of the low DALY burden is the low mortality associated with these diseases and the low disability weight given to these infections and their sequelae in the burden of disease estimates. Van der Werf et al. (2003) and Michaud et al. (2003) examine the argument that the burden of disease figures for the worm diseases are too low due to mis-attribution of mortality, a significant problem when disease diagnosis is imperfect and co-infection is common; while they find some evidence that the true burden may be somewhat higher than stated in the Global Burden of Disease 2002 (WHO, 2004), they conclude that any likely upward revision would not change the absolute burden substantially, or the relative ranking of these diseases. King et al. (2005) focus on the 0.005 disability weight for schistosomiasis (where normal functioning has a weight of 0 and 1 corresponds to death) set by a panel of experts and used in Global Burden of Disease estimates. They argue that schistosomiasis infection produces a large disease burden in terms of anaemia, diarrhoea, low weight for height and reduced physical fitness, and that a more accurate disability weight would be between 0.02 and 0.15, increasing the global DALY burden by a factor between 4 and 30. These ‘hidden’ morbidities, which are difficult to ascribe to a disease at the individual level, but evident in population studies, are also likely to be present in other parasitic diseases. Attributing a higher disease burden to the ‘neglected’ tropical diseases usually implies that we estimate a lower burden for other diseases. At present, a portion of the morbidity associated with the tropical diseases may be mis-attributed to nutritional deficiencies, since many of the symptoms are similar (Crompton and Nesheim, 2002; Stephenson, 1987; Stephenson et al., 2000; Stoltzfus, 1998). Even within the tropical diseases, co-infection is common and can have greater than additive effects. Infection with worms can make malaria episodes more severe (Le Hesran et al., 2004; Spiegel et al., 2003) so making it difficult to attribute illness between malaria and worms. However, a focus on the burden of disease is misleading. The overall burden due to a disease should not be the criterion for priority setting. If there are no effective interventions, prioritizing a high burden disease results in resources being employed to no benefit. If we want to maximize the reduction in the total disease burden with a given budget we should prioritize cost-effective interventions. Prioritizing the most cost-effective interventions maximizes the health (e.g. DALYs) gained per dollar spent. This means that a given health budget will have the greatest impact on the global burden if it uses the most cost-effective interventions first, moving to less cost-effective measures only when the more cost-effective have been exhausted. While the global burden of disease does not provide a ranking for priority setting, it is important insofar as the burden affects cost-effectiveness. The burden of a disease on an individual will determine the health benefits of the intervention, and a higher disability weight will tend to increase the estimated cost-effectiveness of interventions. In addi-
501 tion, in cases where projects have high fixed costs, a high disease prevalence or burden will tend to raise the costeffectiveness of interventions, since the fixed costs can be spread over a larger number of cases or greater total health gains. For example, the potential gains to research are proportional to the burden of disease, while research costs are fixed independently of the scale of the epidemic; this means research should focus on diseases with high burdens. Similarly, the benefits of screening for a disease or populationwide preventive measures depend on the prevalence and total burden, which determines the proportion of cases in which the intervention can have an effect on its target and the potential benefits from doing this. Administrative inputs from the highest levels of government and international organizations form another potential fixed cost. While the burden or prevalence of a disease can affect the cost-effectiveness of interventions, it is still the costeffectiveness that should ultimately be used for priority setting if we wish to maximize health gains. The treatment of high prevalence tropical diseases by mass chemotherapy is highly cost effective with general or school-based populations. There exist cheap drugs and those that are donated free of charge, that can be administered safely to populations and have a large impact, curing the disease in patients and interrupting transmission. Onchocerciasis control, using ivermectin which is donated free of charge by Merck, has a cost of $14—30 per DALY saved (Waters et al., 2004). School-based programmes for intestinal helminthiasis and schistosomiasis cost between $6 and $33 per DALY gained (Warren et al., 1993). High prevalence rates means that it makes sense to avoid the costs of diagnosis and to treat everyone in the population at risk. However, when prevalence rates fall to very low levels after a successful population-level intervention, it is eventually more cost-effective to carry out treatment only when the disease is diagnosed in primary health care clinics. In some cases, for example lymphatic filariasis, we can even proceed to elimination of the disease (Molyneux and Zagaria, 2002). Vertical interventions are therefore likely to give way to interventions through primary health care providers once prevalence rates become low (Ageel and Amin, 1997). It may also make sense to group interventions by delivery methods to achieve economics of scope. Programmes of mass drug administration, whether in populations or in schools are obvious candidates for amalgamation, although integrating the treatment of co-endemic diseases in a single programme will usually mean taking several drugs simultaneously, raising the prospect of drug interactions and a need for clear guidelines on drug use. Cost-effectiveness measures the cost per unit of health gained. A full economic cost—benefit analysis would translate the heath gain into dollar values, and add economic benefits, for comparison against the cost. This approach would also allow the comparison of the cost—benefit ratio of health interventions with those in other sectors. The problem with the cost—benefit approach is that we have to put a monetary value on health, including a value of life, which many people find objectionable. Failure to do this, however, means that we cannot compare interventions across sectors. The high monetary value of life and health found in international studies (see Viscusi and Aldy, 2003), means that cost-effective health interventions have exceptionally high
502 rankings in terms of cost—benefit ratios. Thus priority setting on cost—benefit grounds would result in large flows from other sectors to the health sector. Arguing that health and income are incommensurable, however, means that there is no way of ranking health relative to the benefits provided by other sectors, and no method of judging the appropriate allocation of resources across sectors. One argument against using DALYs as our measure of heath gain is the rule of rescue. This prioritizes saving lives that are in immediate danger over other health gains. To some extent this could be taken account of by putting low weights on disabilities short of death in the DALY calculations. There is an important issue of how to weight death relative to disability, and some evidence that panels of experts may be out of step with communities and those who suffer from ill health; in general, people put more weight on death relative to disability. While this issue can be addressed by more community involvement in setting DALY weights relative to death for various disabilities, the threat of death used in the rule of rescue is more problematic. The rule prioritizes treatment of those who face imminent death; however, this creates a time inconsistency problem when we compare it with preventive measures. On the rule of rescue criterion we might not be willing to spend a great deal on preventive measures today but willing to spend much greater sums on the same people, to less effect, in ten years time when the infections not prevented become life threatening.
3. The economic benefits of investing in the neglected tropical diseases The main benefit of improved health is in the longer lifespans and freedom from illness that it generates. A full measure of human welfare would include both health and income (e.g. Becker et al., 2005; Nordhaus, 2003). In constructing such a measure it is clear that people value health very highly and that improvements in health are very valuable in money terms (Bloom et al., 2004a). However, there are also wider economic benefits to improved health, mainly in the form of improved worker productivity. Economic analysis of worker productivity emphasizes the role of human capital. Human capital has usually been identified with years of schooling and on-the-job work experience, but a more fundamental approach is to think of human capital as a stock of physical and cognitive abilities (Glewwe, 1996, 2002). Taking this view, health, as well as education, can be viewed as a determinant of the stock of human capital. There is evidence that health investments in children lead to higher incomes in adults (e.g. Schultz, 1999). There is also evidence that population health, as measured by life expectancy, has an effect on output and economic growth at the aggregate level (Bhargava et al., 2001; Bloom et al., 2004b). When we move to the aggregate level, however, there are other mechanisms through which health can affect income. A longer lifespan can increase incentives to save for retirement and to invest in education, since the future benefits of such investments are of longer duration. In addition, lower infant mortality can lead to a reduction in fertility rates, setting off the demographic transition and encouraging higher levels of
Leading Article investment in a smaller number of children (Bloom et al., 2003). These arguments give rise to the possibility of health-led development and use of health investments to jump start the economies of developing countries and achieve the Millennium Development Goals (Anonymous, 2005; Fenwick et al., 2005). However, not all health interventions are equally good as poverty reduction measures. One weakness in the macroeconomic literature is that it emphasizes mortality rather than morbidity, mainly a result of the lack of comparable morbidity data across countries and over time. Gallup and Sachs (2001) find a significant effect of malaria prevalence on economic growth, over and above its effect through increased mortality. Many tropical diseases have relatively low mortality burdens but relatively high potential effects on economic outcomes. There are two important mechanisms through which morbidity affects incomes: the first is the direct effect of adult disease burden on working days lost due to illness and low worker productivity while working when ill. The second is the effect of childhood illness on the cognitive and physical development of children and their subsequent earnings potential as adults. There is abundant evidence of the large effects of the tropical diseases on adults. Focusing just on working days lost as a result of bouts of illness, we find large effects of malaria and lymphatic filariasis (Babu et al., 2002; Ramaiah et al., 2000). Ramaiah and Das (2004) estimate that mass drug administration for lymphatic filariasis in India costs $68.41 per chronic case averted but produces savings, mainly in the form of avoidance of working days lost, of $449. Waters et al. (2004) find that onchocerciasis control programmes in Africa generate economic savings, in the form of fewer working days lost due to illness and increased land availability due to reduced transmission of the parasite, that far exceed their costs. Iron deficiency anaemia, which can result from the parasitic diseases, has more insidious effects, lowering energy levels, worker productivity and wages (Thomas and Frankenberg, 2002). The parasitic worm diseases are most common in children where they have effects on school attendance, literacy and physical development (Bleakley, 2003; Miguel and Kremer, 2004), though the potential for effects on cognitive development are less clear (Dickson et al., 2000). The low costs of interventions that can substantially reduce the burden of the parasitic diseases should make these a high priority. Population- and school-based drug administration is safe and costs very little. It promises large benefits, both in terms of reduced disease burden and economic gains. There is, however, a class of ‘neglected’ tropical diseases that are low priorities for intervention. For some diseases available treatments are costly or rely on early detection, but diagnosis may be difficult and surveillance in low prevalence populations can be expensive per case detected. While diseases may impose large health, as well as social and economic, costs on sufferers, the lack of cost-effective interventions means they have a low priority. In middle-income countries these may become a priority as other, more costeffective interventions are exhausted (for example, Chagas disease in South America).
Priority setting and the ‘neglected’ tropical diseases A final issue is who should pay for interventions? Given the high health and economic benefits and low costs that we have outlined, it might seem that some of the treatments for ‘neglected diseases’ could be financed through user fees. There are three arguments for public funding and provision. One is the externality (i.e. the side-effect or consequence of an economic activity that affects other parties without it being reflected in the cost of goods or services involved) caused by mass drug administration in the form of lower disease transmission, making the public benefit greater than the individual benefit. The second is that while the willingness to pay for the treatment of health problems is high, even among poor people in developing countries, there is much less willingness to spend on preventive measures even when they are more cost-effective. The third argument is that private provision of drugs in developing countries is marred by high levels of counterfeiting. There is therefore a strong argument that cost-effective and poverty-reducing interventions should be a priority of national governments, though in the poorest countries their resources will have to be supplemented with international aid.
4. Conclusions In some cases the neglect of a tropical disease is justified and there are higher priorities for intervention. If we adopt the goal of setting health priorities by the burden of a disease, or by the rule of rescue based on the imminent death of the patient, the ‘neglected’ tropical diseases have little claim to priority, although recent research suggests that the burden of these diseases may be higher than previously thought (King et al., 2005). The ‘neglected’ tropical diseases do not threaten the developed world, which means that there is no ‘enlightened self-interest’ argument to prioritize these diseases and no lobby group of victims in developed countries to argue for increased international aid budgets. However, if our goal is to maximize the health benefits of a fixed health budget, we should prioritize cost-effective interventions. On this criterion, the treatment and control of schistosomiasis, onchocerciasis and the intestinal nematode infections through an integrated system of annual mass drug administration (either of the whole population or in schools) should be a high priority even in the poorest countries. In addition, there is evidence that treating these diseases will reduce iron deficiency anaemia (Bhargava et al., 2003; Stoltzfus et al., 1997), increasing their productivity and wages of adults, and improving physical and educational outcomes for children. These interventions can therefore also be thought of as investments in human capital and should be an integral part of a larger strategy of global poverty reduction.
Acknowledgements The author thanks the editor and anonymous referees for their comments and suggestions.
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LEADING ARTICLE
Priority setting and the ‘neglected’ tropical diseases David Canning Available online 15 March 2006
Summary In this paper David Canning argues that interventions against ‘neglected’ tropical diseases should be thought of as investments in human capital and form an integral part of global poverty reduction. He argues that overall burden of disease should not be the criterion for priority setting; if the goal is to maximize health benefits from a fixed health budget then cost-effective interventions should be prioritized. Whilst many people find objectionable the assignment of a monetary value to health, a cost—benefit approach, combining health and economic benefits, would allow the health sector to present arguments to policy makers, based on the rate of return on investment. Since many health interventions in low-income countries have exceptionally high rankings in terms of cost—benefit ratios, this should result in large flows from other sectors to the health sector. © 2006 Royal Society of Tropical Medicine and Hygiene. Published by Elsevier Ltd. All rights reserved.
1. Introduction Many experts in the tropical ‘neglected diseases’ fear that that these illnesses are being downgraded when it comes to priority setting by the international community. While the Global Fund to fight AIDS, Tuberculosis and Malaria and the Global Alliance for Vaccination and Immunization (GAVI) have been successful in generating funding for their specific causes, the treatment and prevention efforts for other tropical diseases, such as lymphatic filariasis, leishmaniasis, schistosomiasis, trypanosomiasis, onchocerciasis, Chagas disease and the intestinal nematode infections (hookworm disease, trichuriasis and ascariasis), have been less successful at attracting attention and gaining international resources (Hotez et al., 2006). Is the relative position of the ‘neglected diseases’ in priority setting justified? Before answering this question we must first decide on what criteria to use for priority setting; this raises some important issues. The first is that the whole notion of disease priorities presupposes an emphasis on vertical, disease-specific interventions rather than broadbased health care services. Some activities — population
surveillance, treatment and vector control — may require specialized staff and a vertical approach. Even within a broad health care system, there has to be priority setting, and in the poorest developing countries, where health systems function very poorly, timely interventions may require a vertical approach rather than an effort at overall health system expansion and reform. The second issue is the need to emphasize judging priorities by evaluating outcomes. A different approach to priority setting is to emphasize the need for a fair and reasonable decision making process: for example, communities and disease victims should have an input into priority setting and a forum for making their views heard. The third issue is that priority setting in global health is often set up as the question of how best to spend some limited amount of resources. However, a large part of the question is how to generate increased support for health in the poorest countries of the world from more developed countries. While ‘best use’ of the resources may itself be attractive to donors, it is important to recognize that international donors may have other interests, over and above generating health. There are three areas in which this dif-
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500 ference in interests is important. The first is for infectious diseases that threaten developed countries. The second is when a disease is present in both developed and developing countries in a way that creates a common bond between sufferers. The high priority given to SARS and HIV/AIDS is in part due to these effects. The third is that wellbeing extends beyond health, and the international community has made poverty reduction a major goal, so that priority setting within the health sector has to take account of how it meets the goal of poverty reduction as well as improving health. This third issue is, of course, not one just for international donors, for even within a country an argument that health interventions reduce poverty is a powerful incentive to increase the health budget. It is difficult to argue for prioritizing most ‘neglected’ tropical diseases on the grounds that they spread to the developed world or to appeal to a community of sufferers in developed countries. However, as we shall see, there is a strong argument for some of the ‘neglected’ tropical diseases that investments in their control can be viewed as much as economic investments in human capital and worker productivity as health interventions and can be justified on those grounds. First we turn to the usual arguments for priority setting to improve health, given a fixed budget, and evaluate how the ‘neglected diseases’ perform on each criterion. We first consider the burden of disease. On this criterion the ‘neglected diseases’ fare badly since the bulk of the burden of infectious disease in developing countries comes from AIDS, tuberculosis and malaria, though recent research suggests that the morbidity burden of some neglected diseases may have been underestimated (King et al., 2005). The second is cost-effectiveness; on this criterion, some of the ‘neglected diseases’ do very well, with very cheap and effective cures and preventive measures being available. The third criterion is the moral imperative of the ‘rule of rescue’, the idea that we should prioritize diseases that pose an imminent threat to life; on this criterion, the most ‘neglected diseases’ do badly, since they are often chronic, but not life-threatening, conditions. We argue that it is difficult to justify the burden of disease, or the rule of rescue, as reasonable criteria for priority setting. If we accept we are trying to maximize the health produced, or death and disability avoided, we are led to prioritize interventions according to their cost-effectiveness. A number of the ‘neglected’ tropical diseases, notably onchocerciasis, filariasis and the intestinal nematode infections, have highly cost-effective interventions which are based on annual oral administration of drugs to the whole population in endemic areas and should be high priorities in terms of improving population health. In addition, to these population-based interventions, more targeted preventive interventions on groups with high prevalence rates, particularly infants and schoolchildren, can be used to prevent helminthic infections, schistosomiasis and blinding trachoma. These interventions also promise large economic payoffs, indeed they could be justified purely as economic interventions to increase educational outcomes and worker productivity, even in the absence of the health benefits. Thinking of these interventions as investments in human capital as part of a poverty reduction programme, as well
Leading Article as part of a health programme, would make them more attractive to policy makers outside the heath sector. This requires moving from cost-effectiveness estimates (the cost per unit of health outcome) to research that estimates the rate of return to these interventions as human capital investments (the discounted flow of increased earnings relative to the cost) to allow comparison with other human capital investments, such as education, thereby facilitating priority setting across sectors. While priority setting in terms of individual diseases may be justified, interventions that combine the treatment of several diseases in a common delivery method are likely to be more cost-effective. A good example is the GAVI initiative that targets a variety of diseases that can be prevented by vaccination. Grouping tropical and infectious diseases by treatment, for example, school-based or population-based annual mass drug distribution, or bednet use, and delivering treatments simultaneously, or using the same health sector infrastructure, is likely to produce a more attractive ‘packaged’ intervention than targeting each disease separately. Tackling the diseases outlined above, through populationor school-based drug administration, may be so cheap and have such large health and economic benefits that, as advocated by Molyneux (2004) and Molyneux et al. (2005), they should be a high priority even in the poorest countries. However, not all ‘neglected diseases’ are alike. For some, such as Chagas disease, dengue and leishmaniasis, vector control is the best hope for reducing the disease burden, but vector control is difficult and requires substantial expertise and commitment. Even in the case of malaria, treatment and vector control has proved difficult despite substantial resources being committed (Attaran, 2004). For others such as Buruli ulcer, early detection and treatment are the best course since treatment in the later stages, often involving surgery when the symptoms of the disease have become evident, is less beneficial and is expensive. However, early detection requires the correct diagnosis when symptoms are not obvious, and this requires a high standard of primary health care to be available. On cost-effectiveness grounds, and as economic investments, these should only be undertaken once other, more cost-effective interventions have been exhausted.
2. Priority setting for health One tool used for priority setting is the burden of disease. Taking death due to a disease, or some measure that incorporates morbidity as well as mortality, such as quality adjusted life years (QALYs) or disability adjusted life years (DALYs) gives an estimate of the total costs in terms of health loss imposed by a disease. Global burden of disease data for 2002, from the World Health Report (WHO, 2004), show that in Africa around 52% of the disease burden comes from infectious diseases. However, the DALY burden due to the ‘neglected’ tropical diseases and the worm infections is estimated to be only 4% of the total due to infectious disease: HIV/AIDS; malaria; the diarrhoeal diseases, such as cholera and rotavirus that are usually associated with lack of clean water and sanitation; the childhood cluster of disease, such as measles; and tuberculosis make up the vast majority of the burden.
Priority setting and the ‘neglected’ tropical diseases One response to this low disease burden is that is it based on mis-estimation. We can contrast the low estimate of the disease burden with the high prevalence rates for schistosomiasis and worm diseases in sub-Saharan Africa (De Silva et al., 2003): between 24% and 29% of the population are infected with each of trichuriasis, ascariasis, hookworm and schistosomiasis. The explanation of the low DALY burden is the low mortality associated with these diseases and the low disability weight given to these infections and their sequelae in the burden of disease estimates. Van der Werf et al. (2003) and Michaud et al. (2003) examine the argument that the burden of disease figures for the worm diseases are too low due to mis-attribution of mortality, a significant problem when disease diagnosis is imperfect and co-infection is common; while they find some evidence that the true burden may be somewhat higher than stated in the Global Burden of Disease 2002 (WHO, 2004), they conclude that any likely upward revision would not change the absolute burden substantially, or the relative ranking of these diseases. King et al. (2005) focus on the 0.005 disability weight for schistosomiasis (where normal functioning has a weight of 0 and 1 corresponds to death) set by a panel of experts and used in Global Burden of Disease estimates. They argue that schistosomiasis infection produces a large disease burden in terms of anaemia, diarrhoea, low weight for height and reduced physical fitness, and that a more accurate disability weight would be between 0.02 and 0.15, increasing the global DALY burden by a factor between 4 and 30. These ‘hidden’ morbidities, which are difficult to ascribe to a disease at the individual level, but evident in population studies, are also likely to be present in other parasitic diseases. Attributing a higher disease burden to the ‘neglected’ tropical diseases usually implies that we estimate a lower burden for other diseases. At present, a portion of the morbidity associated with the tropical diseases may be mis-attributed to nutritional deficiencies, since many of the symptoms are similar (Crompton and Nesheim, 2002; Stephenson, 1987; Stephenson et al., 2000; Stoltzfus, 1998). Even within the tropical diseases, co-infection is common and can have greater than additive effects. Infection with worms can make malaria episodes more severe (Le Hesran et al., 2004; Spiegel et al., 2003) so making it difficult to attribute illness between malaria and worms. However, a focus on the burden of disease is misleading. The overall burden due to a disease should not be the criterion for priority setting. If there are no effective interventions, prioritizing a high burden disease results in resources being employed to no benefit. If we want to maximize the reduction in the total disease burden with a given budget we should prioritize cost-effective interventions. Prioritizing the most cost-effective interventions maximizes the health (e.g. DALYs) gained per dollar spent. This means that a given health budget will have the greatest impact on the global burden if it uses the most cost-effective interventions first, moving to less cost-effective measures only when the more cost-effective have been exhausted. While the global burden of disease does not provide a ranking for priority setting, it is important insofar as the burden affects cost-effectiveness. The burden of a disease on an individual will determine the health benefits of the intervention, and a higher disability weight will tend to increase the estimated cost-effectiveness of interventions. In addi-
501 tion, in cases where projects have high fixed costs, a high disease prevalence or burden will tend to raise the costeffectiveness of interventions, since the fixed costs can be spread over a larger number of cases or greater total health gains. For example, the potential gains to research are proportional to the burden of disease, while research costs are fixed independently of the scale of the epidemic; this means research should focus on diseases with high burdens. Similarly, the benefits of screening for a disease or populationwide preventive measures depend on the prevalence and total burden, which determines the proportion of cases in which the intervention can have an effect on its target and the potential benefits from doing this. Administrative inputs from the highest levels of government and international organizations form another potential fixed cost. While the burden or prevalence of a disease can affect the cost-effectiveness of interventions, it is still the costeffectiveness that should ultimately be used for priority setting if we wish to maximize health gains. The treatment of high prevalence tropical diseases by mass chemotherapy is highly cost effective with general or school-based populations. There exist cheap drugs and those that are donated free of charge, that can be administered safely to populations and have a large impact, curing the disease in patients and interrupting transmission. Onchocerciasis control, using ivermectin which is donated free of charge by Merck, has a cost of $14—30 per DALY saved (Waters et al., 2004). School-based programmes for intestinal helminthiasis and schistosomiasis cost between $6 and $33 per DALY gained (Warren et al., 1993). High prevalence rates means that it makes sense to avoid the costs of diagnosis and to treat everyone in the population at risk. However, when prevalence rates fall to very low levels after a successful population-level intervention, it is eventually more cost-effective to carry out treatment only when the disease is diagnosed in primary health care clinics. In some cases, for example lymphatic filariasis, we can even proceed to elimination of the disease (Molyneux and Zagaria, 2002). Vertical interventions are therefore likely to give way to interventions through primary health care providers once prevalence rates become low (Ageel and Amin, 1997). It may also make sense to group interventions by delivery methods to achieve economics of scope. Programmes of mass drug administration, whether in populations or in schools are obvious candidates for amalgamation, although integrating the treatment of co-endemic diseases in a single programme will usually mean taking several drugs simultaneously, raising the prospect of drug interactions and a need for clear guidelines on drug use. Cost-effectiveness measures the cost per unit of health gained. A full economic cost—benefit analysis would translate the heath gain into dollar values, and add economic benefits, for comparison against the cost. This approach would also allow the comparison of the cost—benefit ratio of health interventions with those in other sectors. The problem with the cost—benefit approach is that we have to put a monetary value on health, including a value of life, which many people find objectionable. Failure to do this, however, means that we cannot compare interventions across sectors. The high monetary value of life and health found in international studies (see Viscusi and Aldy, 2003), means that cost-effective health interventions have exceptionally high
502 rankings in terms of cost—benefit ratios. Thus priority setting on cost—benefit grounds would result in large flows from other sectors to the health sector. Arguing that health and income are incommensurable, however, means that there is no way of ranking health relative to the benefits provided by other sectors, and no method of judging the appropriate allocation of resources across sectors. One argument against using DALYs as our measure of heath gain is the rule of rescue. This prioritizes saving lives that are in immediate danger over other health gains. To some extent this could be taken account of by putting low weights on disabilities short of death in the DALY calculations. There is an important issue of how to weight death relative to disability, and some evidence that panels of experts may be out of step with communities and those who suffer from ill health; in general, people put more weight on death relative to disability. While this issue can be addressed by more community involvement in setting DALY weights relative to death for various disabilities, the threat of death used in the rule of rescue is more problematic. The rule prioritizes treatment of those who face imminent death; however, this creates a time inconsistency problem when we compare it with preventive measures. On the rule of rescue criterion we might not be willing to spend a great deal on preventive measures today but willing to spend much greater sums on the same people, to less effect, in ten years time when the infections not prevented become life threatening.
3. The economic benefits of investing in the neglected tropical diseases The main benefit of improved health is in the longer lifespans and freedom from illness that it generates. A full measure of human welfare would include both health and income (e.g. Becker et al., 2005; Nordhaus, 2003). In constructing such a measure it is clear that people value health very highly and that improvements in health are very valuable in money terms (Bloom et al., 2004a). However, there are also wider economic benefits to improved health, mainly in the form of improved worker productivity. Economic analysis of worker productivity emphasizes the role of human capital. Human capital has usually been identified with years of schooling and on-the-job work experience, but a more fundamental approach is to think of human capital as a stock of physical and cognitive abilities (Glewwe, 1996, 2002). Taking this view, health, as well as education, can be viewed as a determinant of the stock of human capital. There is evidence that health investments in children lead to higher incomes in adults (e.g. Schultz, 1999). There is also evidence that population health, as measured by life expectancy, has an effect on output and economic growth at the aggregate level (Bhargava et al., 2001; Bloom et al., 2004b). When we move to the aggregate level, however, there are other mechanisms through which health can affect income. A longer lifespan can increase incentives to save for retirement and to invest in education, since the future benefits of such investments are of longer duration. In addition, lower infant mortality can lead to a reduction in fertility rates, setting off the demographic transition and encouraging higher levels of
Leading Article investment in a smaller number of children (Bloom et al., 2003). These arguments give rise to the possibility of health-led development and use of health investments to jump start the economies of developing countries and achieve the Millennium Development Goals (Anonymous, 2005; Fenwick et al., 2005). However, not all health interventions are equally good as poverty reduction measures. One weakness in the macroeconomic literature is that it emphasizes mortality rather than morbidity, mainly a result of the lack of comparable morbidity data across countries and over time. Gallup and Sachs (2001) find a significant effect of malaria prevalence on economic growth, over and above its effect through increased mortality. Many tropical diseases have relatively low mortality burdens but relatively high potential effects on economic outcomes. There are two important mechanisms through which morbidity affects incomes: the first is the direct effect of adult disease burden on working days lost due to illness and low worker productivity while working when ill. The second is the effect of childhood illness on the cognitive and physical development of children and their subsequent earnings potential as adults. There is abundant evidence of the large effects of the tropical diseases on adults. Focusing just on working days lost as a result of bouts of illness, we find large effects of malaria and lymphatic filariasis (Babu et al., 2002; Ramaiah et al., 2000). Ramaiah and Das (2004) estimate that mass drug administration for lymphatic filariasis in India costs $68.41 per chronic case averted but produces savings, mainly in the form of avoidance of working days lost, of $449. Waters et al. (2004) find that onchocerciasis control programmes in Africa generate economic savings, in the form of fewer working days lost due to illness and increased land availability due to reduced transmission of the parasite, that far exceed their costs. Iron deficiency anaemia, which can result from the parasitic diseases, has more insidious effects, lowering energy levels, worker productivity and wages (Thomas and Frankenberg, 2002). The parasitic worm diseases are most common in children where they have effects on school attendance, literacy and physical development (Bleakley, 2003; Miguel and Kremer, 2004), though the potential for effects on cognitive development are less clear (Dickson et al., 2000). The low costs of interventions that can substantially reduce the burden of the parasitic diseases should make these a high priority. Population- and school-based drug administration is safe and costs very little. It promises large benefits, both in terms of reduced disease burden and economic gains. There is, however, a class of ‘neglected’ tropical diseases that are low priorities for intervention. For some diseases available treatments are costly or rely on early detection, but diagnosis may be difficult and surveillance in low prevalence populations can be expensive per case detected. While diseases may impose large health, as well as social and economic, costs on sufferers, the lack of cost-effective interventions means they have a low priority. In middle-income countries these may become a priority as other, more costeffective interventions are exhausted (for example, Chagas disease in South America).
Priority setting and the ‘neglected’ tropical diseases A final issue is who should pay for interventions? Given the high health and economic benefits and low costs that we have outlined, it might seem that some of the treatments for ‘neglected diseases’ could be financed through user fees. There are three arguments for public funding and provision. One is the externality (i.e. the side-effect or consequence of an economic activity that affects other parties without it being reflected in the cost of goods or services involved) caused by mass drug administration in the form of lower disease transmission, making the public benefit greater than the individual benefit. The second is that while the willingness to pay for the treatment of health problems is high, even among poor people in developing countries, there is much less willingness to spend on preventive measures even when they are more cost-effective. The third argument is that private provision of drugs in developing countries is marred by high levels of counterfeiting. There is therefore a strong argument that cost-effective and poverty-reducing interventions should be a priority of national governments, though in the poorest countries their resources will have to be supplemented with international aid.
4. Conclusions In some cases the neglect of a tropical disease is justified and there are higher priorities for intervention. If we adopt the goal of setting health priorities by the burden of a disease, or by the rule of rescue based on the imminent death of the patient, the ‘neglected’ tropical diseases have little claim to priority, although recent research suggests that the burden of these diseases may be higher than previously thought (King et al., 2005). The ‘neglected’ tropical diseases do not threaten the developed world, which means that there is no ‘enlightened self-interest’ argument to prioritize these diseases and no lobby group of victims in developed countries to argue for increased international aid budgets. However, if our goal is to maximize the health benefits of a fixed health budget, we should prioritize cost-effective interventions. On this criterion, the treatment and control of schistosomiasis, onchocerciasis and the intestinal nematode infections through an integrated system of annual mass drug administration (either of the whole population or in schools) should be a high priority even in the poorest countries. In addition, there is evidence that treating these diseases will reduce iron deficiency anaemia (Bhargava et al., 2003; Stoltzfus et al., 1997), increasing their productivity and wages of adults, and improving physical and educational outcomes for children. These interventions can therefore also be thought of as investments in human capital and should be an integral part of a larger strategy of global poverty reduction.
Acknowledgements The author thanks the editor and anonymous referees for their comments and suggestions.
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