Note: In September 2011, we confirmed a number of errors in the estimates for the cost-effectiveness of deworming published in the Disease Control Priorities report. Based on those findings, we are currently rethinking our use of cost-effectiveness estimates, like the DCP2's, for which the full details of the calculations are not public. For more information, see our blog post on the topic.The content on this page still needs to be updated to reflect our findings.
In a nutshell
- The Problem: Infection of parasites can cause chronic malnutrition, pain, and anemia (and in some cases death). More on schistosomiasis here; more on soil-transmitted helminths here.
- The Program: Mass administration of both praziquantel, to treat schistosomiasis, and another drug (usually albendazole), to treat soil-transmitted helminths.
- Track record: Praziquantel's effectiveness has been established in high-quality studies; the effectiveness of albendazole is slightly less clear, although we believe the weight of the evidence supports it.
- Cost-effectiveness: Combination deworming is among the most cost-effective programs, and has been credibly estimated to cost only $3.50 for every additional year of school attendance for children.
- Bottom line: Combination deworming is a proven, inexpensive method for improving lives in the developing world.
Basics of the program
What is the program? What problem does it target?Infection of parasites can cause chronic malnutrition, pain, and anemia (and in some cases death). (More on schistosomiasis; more on soil-transmitted helminths) The Word Health Organization recommends treatment with praziquantel at least three times in childhood1 for schistosomiasis to cure non-severe morbidity and prevent the development of severe symptoms later in life.2 A variety of anthelmintic drugs are recommended for controlling soil-transmitted helminths.3 The World Health Organization recommends treatment 2-3 times per year in areas of intense transmission and annually in areas of lower transmission intensity.4
What are the components required to implement this program - how does it work?This program requires anthelmintic drugs and a means of distributing them as widely and efficiently as possible. Drugs: Prazinquatel is available free of charge in some high disease burdened areas through donations from Merck.5 GlaxoSmithKline also donates significant amounts of albendazole, although it stresses the role of this drug in combating a different disease (lymphatic filariasis) and it's unclear whether it makes albendazole available specifically for the purpose of deworming.6 Distribution mechanism: The Disease Control Priorities in Developing Countries report states that schools provide a strong infrastructure for administration and that teachers can be trained to deliver drugs safely.7 In the absence of training, mobile teams can come in to implement drug administration, but this method can cost significantly more.8
Program track record
Micro evidence: Has this program been rigorously evaluated and shown to work?Praziquantel's effectiveness has been established in high-quality studies; the effectiveness of albendazole is slightly less clear, although we believe the weight of the evidence supports its use. One high-quality evaluation provides evidence of the combination program improving school attendance, detailed below.
Praziquantel to control schistosomiasisA Cochrane review of 24 randomized and quasi-randomized controlled trials included 6,315 participants in interventions to treat urinary schistosomiasis. The review concluded that "praziquantel and metrifonate are effective treatments for urinary schistosomiasis and have few adverse events. Metrifonate requires multiple administrations and is therefore operationally less convenient in community-based control programmes."9 A Cochrane review of 13 randomized or pseudo-randomized trials treating intestinal schistosomiasis concluded that "oxamniquine and praziquantel both appear to be effective for treatment of S. mansoni, although lower doses of oxamniquine (less than 30 mg/kg) may not be as effective in some areas."10
Drugs targeted at soil-transmitted helminthsA recent Cochrane review finds 34 high-quality evaluations of anthelmintic drugs' effects on various health and well-being measures, including weight and school attendance and performance. The review found that "after just one dose children's weight improved, and more doses did not seem to improve this further. Only one of the seven trials that assessed school performance found any positive effect, so it seems unlikely that there is a benefit here. Two trials looked at adverse events, but the trials were small. Further research is needed."11 The full review lays out the full results of each of the trials.12 The Disease Control Priorities in Developing Countries report has a more optimistic take on the available evidence, asserting that anthelmintics of this kind have been associated with positive effects in nutritional status, cognitive development, and infant survival.13 However, the Cochrane review cited above is more recent, appears more comprehensive, and lays out its full criteria, sources and results (unlike the Disease Control Priorities in Developing Countries report). Another response to the Cochrane paper argues that most of the studies are not reliable because they compared treated to non-treated children within the same school; there is evidence (see directly below) that treating some children in a school reduces the infection rates of all children. Thus, a study comparing treated to non-treated children may show no effects on treated children even if the treatments improved outcomes for all children.14
Combination programA study conducted in Kenya used alphabetical ordering to separate 75 schools into three groups of 25; each group of schools received the same combination program (albendazole for all children; praziquantel for children in schools with high schistosomiasis prevalence), but started the program in different periods. Comparing the schools, the study found that the program decreased school absenteeism by one-quarter, though test scores did not change.15 The authors argue that comparing groups of schools to each other is a more reliable test of this sort of program than comparing individuals within a school to each other, since treating some children in a school may reduce infection rates for all children (due to the way the disease is transmitted).16
Macro evidence: Has this program played a role in large-scale success stories?We have identified no such success stories. (More on the general idea of "macro evidence".)
Recommendations and concerns
Do expert reviews of the comparative merits of interventions endorse this one?See sources consulted.
- The Copenhagen Consensus endorses combination deworming, ranking it as the 6th most promising intervention overall.17
- The Disease Control Priorities in Developing Countries report states, "Until new technologies become available, anthelmintic chemotherapy for school-age children remains the most practical and substantive means to control [soil-transmitted helminths] and schistosome infections in the developing world."18
- Jamison, Jha, and Bloom (2008) do not rank combination deworming in their table of "Key Investment Priorities,"19 but they do state:
In addition to interventions to reduce under-five mortality, one other priority is clear. The world's most prevalent infections are intestinal helminth (worm) infections, and children of all ages are among the most heavily affected. Hotez, et al. (2006) discuss these infections, which a low-cost drug (albendazole), taken every six months to a year, can control effectively... Use of albendazole is only an interim solution, but it is one that may be required for decades if the experience of the currently high-income countries is relevant.20
What versions of the intervention are best?Three versions of this intervention are (1) population intervention, where everyone in a region is treated; (2) targeted intervention, where certain demographic subgroups are treated; and (3) selective intervention, where individuals selected by diagnosis or suspicion of infection are treated.21 The World Health Organization recommends population deworming (treatment for all people in an area of high infection) is recommended for controlling soil-transmitted helminths22 and targeted treatment for schistosomiasis.23 Treating school-aged children as a targeted population group is the version that has been most closely evaluated.24 It also may be the most cost-effective because school-aged children typically have the highest rate of helminth infection and reinfection, and schools offer an infrastructure for delivery.25
Cost-effectivenessThe Disease Control Priorities Report estimates that the costs of this program are "as low as US $0.25 per child" treated26, and $8-19 per disability-adjusted life-year (DALY) averted.27 Separately, a high-quality evaluation of a school-based deworming program in Kenya estimates costs of $0.49 per child treated and $5 per DALY averted.28 (More on the DALY metric.) The Kenya evaluation, examining the effect of deworming on school attendance rates, also estimates that the program costs $3.50 per additional year of schooling per child (when administered to children).29
- Bundy, D., et al. 2009. Deworming and development: Asking the right questions, asking the questions right (PDF). PLoS Negl Trop Dis 3(1): e362.
- Copenhagen Concensus Center. Copenhagen Consensus 2008 - Results (PDF).
- Danso-Appiah, A., et al. 2008. Drugs for treating urinary schistosomiasis. Cochrane Database of Systematic Reviews 2008, Issue 3. Summary available at http://www.cochrane.org/reviews/en/ab000053.html (accessed April 26, 2010). Archived by WebCite® at http://www.webcitation.org/5pHThGp7G.
- GiveWell. Website:
- GlaxoSmithKline. Eliminating lymphatic filariasis. http://www.gsk.com/infocus/eliminating.htm (accessed April 23, 2010). Archived by WebCite® at http://www.webcitation.org/5pCnU1n73.
- Jamison, Dean T., et al., eds. 2006. Disease control priorities in developing countries (PDF). 2nd ed. New York: Oxford University Press.
- Jamison, Dean, Prabhat Jha, and David Bloom. 2008. Copenhagen Consensus 2008 challenge paper: Diseases (PDF).
- Miguel, Edward and Michael Kremer. 2004. Worms: Identifying impacts on education and health in the presence of treatment externalities (PDF). Econometrica 72: 159–217.
- Saconato, Humberto, and Ãlvaro N. Atallah. 1999. Interventions for treating schistosomiasis mansoni. Cochrane Database of Systematic Reviews 1999, Issue 3. Summary available at http://www.cochrane.org/reviews/en/ab000528.html (accessed April 26, 2010). Archived by WebCite® at http://www.webcitation.org/5pHTwwC6J.
- Taylor-Robinson, David C., Ashley P. Jones, and Paul Garner. Deworming drugs for treating soil-transmitted intestinal worms in children: effects on growth and school performance. Cochrane Database of Systematic Reviews 2007, Issue 4. Summary available at http://www.cochrane.org/reviews/en/ab000371.html (accessed April 26, 2010). Archived by WebCite® at http://www.webcitation.org/5pHU5GBgg.
- World Health Organization. Schistosomiasis. http://www.who.int/mediacentre/factsheets/fs115/en/index.html (accessed April 26, 2010). Archived by WebCite® at http://www.webcitation.org/5pHUQjziH.
- World Health Organization. Schistosomiasis: Strategy. http://www.who.int/schistosomiasis/strategy/en/ (accessed April 26, 2010. Archived by WebCite® at http://www.webcitation.org/5pHUa8rZp.
- 1. "Treatment at least three times during childhood is likely to prevent disease in adulthood." World Health Organization, "Schistosomiasis: Strategy."
- 2. "Recommended intervention strategy and aim: Targeted distribution of praziquantel is the norm. Intervention frequency is determined by the prevalence of infection or of visible haematuria (for urinary schistosomiasis only) among school-age children. The aim is morbidity control: periodic treatment of at-risk populations will cure subtle morbidity and prevent infected individuals from developing severe, late-stage morbidity due to schistosomiasis." World Health Organization, "Schistosomiasis."
- 3. "Recommended drugs for use in public health interventions to control STH infection are the benzimidazole anthelmintics (BZAs), albendazole (single dose: 400mg, reduced to 200mgfor children between 12 and 24 months), or mebendazole (single dose: 500 mg), as well as levamisole or pyrantel pamoate (WHO 2002)." Jamison et al. 2006, Pgs 472-3.
- 4. "To control morbidity in areas of intense transmission (prevalence greater than 70 percent and more than 10 percent of moderate and heavy-intensity infection), WHO (2002) recommends treatment two or three times a year for STH [soil-transmitted helminth] infections. In areas with a lower intensity of transmission (prevalence between 40 and 60 percent and less than 10 percent of moderate- and heavy-intensity infection), intervention once a year is recommended (WHO 2002)." Jamison et al. 2006, Pg 473.
- 5. "Praziquantel is now available free of charge to a few high-disease burden least developed countries (LDC), through a donation from Merck KGaA to the World Health Organization. The donation of praziquantel is based on a successful review of the national plan for schistosomiasis control and a commitment of resources for implementation." World Health Organization, "Schistosomiasis: Strategy."
- 6. "In 1998, GSK formed a partnership with the World Health Organization (WHO) to eliminate LF, and committed to donate its antiparasitic medicine, albendazole, to all countries at risk for as long as necessary to eliminate the disease as a public health problem." GlaxoSmithKline, "Eliminating Lymphatic Filariasis."
- 7. "Schools offer a readily available, extensive, and sustained infrastructure with a skilled workforce that is in close contact with the community. With support from the local health system, teachers can deliver the drugs safely. Teachers need only a few hours of training to understand the rationale for deworming and to learn how to give out the pills and keep a record of their distribution." Jamison et al. 2006, Pg 473.
- 8. "Integrating drug distribution through the school system rather than using mobile teams, along with a marked decline in the price of BZAs and PZQ, has resulted in a 10-fold reduction in delivery costs. However, those costs are artificially low because they do not include the external costs for the coordinating center responsible for supporting those approaches (Guyatt 2003)." Jamison et al. 2006, Pg 475.
- 9. Danso-Appiah et al. 2008, Pg 2.
- 10. Saconato and Atallah 1999, Pg 1.
- 11. Taylor-Robinson, Jones, and Garner, Pg 2.
- 12. The technical summary of results states, "Thirty-four RCTs, including six cluster-RCTs, met the inclusion criteria. Four trials had adequate allocation concealment, and three cluster-RCTs failed to take design effects into account in their analysis. Weight increased after one dose of a deworming drug (MD0.34 kg, 95% CI 0.05 to 0.64, RE model; 2448 children, 9 trials); however, there was considerable heterogeneity between trials that was not explained by background intestinal worm infection or intensity. A meta-analysis of multiple dose trials reporting on outcomes within a year of starting treatment showed no significant difference in weight gain (1714 children, 6 trials); however, one cluster-RCT did show effects on weight at one year in a subgroup analysis. In the seven multiple dose trials with follow up beyond 12 months, only one showed a signiï¬cant increase in weight. Six of seven trials reported clear data on cognitive tests and school performance: ï¬ve reported no signiï¬cant effects, and one showed some improvements in three out of 10 cognitive tests." Taylor-Robinson, Jones, and Garner, Pg 1-2.
- 13. "Preschool children. Periodic distribution of anthelmintics has a positive effect on motor and language development and reduces malnutrition in very young children (Stoltzfus and others 2004). School-age children. Treating school-age children has a considerable effect on their nutritional status (Stoltzfus and others 2004), anemia, physical fitness, appetite, growth (Stephenson, Latham, and Ottesen 2000), and intellectual development (Drake and others 2000). Women of reproductive age. Studies of pregnant women conducted by Christian, Khatry, and West (2004) in Nepal indicate that albendazole treatment improves maternal hemoglobin as well as birth-weight and child survival." Jamison et al. 2006, Pg 474.
- 14. Bundy et al. 2009.
- 15. "The program reduced school absenteeism in treatment schools by one-quarter...Yet we do not find evidence that deworming improved academic test scores." Miguel and Kremer 2004, Pg 159.
- 16. "Existing studies randomize the provision of deworming treatment within schools to treatment and placebo groups, and then examine the impact of deworming on cognitive outcomes. Their within-school randomization designs prevent existing studies from credibly estimating externality benefits. Moreover, the difference in educational outcomes between the treatment and placebo groups understates the actual impact of deworming on the treatment group if placebo group pupils also experience health gains due to local treatment externalities. In fact, re-examination of these recent randomized studies suggests that untreated placebo pupils often experienced substantial worm load reductions, as would be consistent with the hypothesis of within-school externalities." Miguel and Kremer 2004, Pg 163.
- 17. Copenhagen Consensus, "Copenhagen Consensus 2008 - Results," Pg 2.
- 18. Jamison et al. 2006, Pg 480.
- 19. Jamison, Jha, and Bloom 2008, Pg 51.
- 20. Jamison, Jha, and Bloom 2008, Pg 33.
"Drug treatment can be administered in the community using different strategies:
- Universal treatment. The entire community is treated, irrespective of age, sex, infection status, and other characteristics.
- Targeted treatment. Treatment targets population groups, which may be defined by age, sex, or other social characteristics, irrespective of the infectious status.
- Selective treatment. Treatment targets individual-level application of anthelmintic drugs, which is selected on the basis of either diagnosis or a suspicion of current infection." Jamison et al. 2006, Pg 472.
- 22. "The recommended strategy for helminth control is a population-based approach, in which individuals in targeted communities are treated irrespective of their infection status (WHO 2002). This strategy is justified for several reasons, including the simplicity and safety of delivering treatment. Individual diagnosis is difficult and expensive and offers no safety benefit." Jamison et al. 2006, Pg 473.
- 23. "Recommended intervention strategy and aim: Targeted distribution of praziquantel is the norm. Intervention frequency is determined by the prevalence of infection or haematuria (for S. haematobium only) among school-age children. The aim is morbidity control: periodic treatment of at-risk populations will cure subtle morbidity and prevent infected individuals from developing severe, late-stage morbidity due to schistosomiasis." World Health Organization, "Schistosomiasis: Strategy."
- 24. "Several studies have evaluated the costs of school-based periodic deworming in several different settings, whereas comparable studies on other interventions are still lacking." Jamison et al. 2006, Pg 474.
- 25. "School-age children typically have the highest intensity of worm infection of any age group, and chronic infection negatively affects all aspects of children's health, nutrition, cognitive development, learning, and educational access and achievement (World Bank 2003). Regular deworming can cost-effectively reverse and prevent much of this morbidity. Furthermore, schools offer a readily available, extensive, and sustained infrastructure with a skilled workforce that is in close contact with the community. With support from the local health system, teachers can deliver the drugs safely. Teachers need only a few hours of training to understand the rationale for deworming and to learn how to give out the pills and keep a record of their distribution. School based deworming also has major externalities for untreated children and the whole community. By reducing transmission in the community of Ascaris and Trichuris infections, deworming substantially improves the health and school participation of both treated and untreated children, both in treatment schools and in neighboring schools (Bundy and others 1990; Miguel and Kremer 2003)." Jamison et al. 2006, Pg 473.
- 26. "For STH infections in Tanzania, Nigeria, and Montserrat, the costs range from US$0.21 to US$0.51 per treatment. However, by training teachers and other school officials to administer anthelmintic drugs, the system could achieve low-cost delivery by 'piggy-backing' on existing programs in the educational sector (WHO 2002). Specific examples of such programs conducted in Ghana and Tanzania are summarized in the section 'Implementation of Control Strategies: Lessons of Experience,' later in this chapter. It was found that delivery of school-based targeted anthelmintic treatment could cost as little as US$0.03 per child, which may be as low as one-tenth of the estimated costs for vertical delivery (WHO 2002). Thus, at current drug prices, the total cost (drug plus delivery) of a single treatment with albendazole or mebendazole may be as low as US$0.05, and that of a combined treatment with PZQ may be as low as US$0.25 per child (WHO 2002)." Jamison et al. 2006, Pg 474.
- 27. "The estimate of cost per DALY is higher for schistosomiasis relative to STH infections because of higher drug costs and lower disability weights. Depending on whether generics or original formulations are used, the cost per DALY averted ranges from US$3.36 to US$6.92. However, in combination, treatment with both albendazole and PZQ proves to be extremely cost effective, in the range of US$8 to US$19 per DALY averted." Jamison et al. 2006, Pg 476.
- 28. "We use deworming program cost estimates from the Partnership for Child Development (PCD (1999)), which reports costs of 0.49 US dollars per pupil per year in a large-scale government intervention in Tanzania...In calculating the overall reduction in disease burden due to the program, we consider overall treatment effects (corrected for cross-school externalities) on the treated in treatment schools, externality effects (corrected for cross-school externalities) on the untreated in treatment schools, and externalities for untreated pupils in comparison schools...Summing these three components of the treatment effect, the total number of DALY's averted as a result of the program is 649, which translates into a cost of approximately $5 per DALY averted, using the costs of the PCD program in Tanzania." Miguel and Kremer 2004, Pg 203-204.
- 29. "Including the externality benefits, the cost per additional year of school participation is only $3.50, making deworming considerably more cost-effective than alternative methods of increasing school participation, such as school subsidies (see Kremer (2003))." Miguel and Kremer 2004, Pg 160.