A note on this page's publication date
The content that appears below was created several years ago. This content is likely to be no longer fully accurate, both with respect to the research it presents and with respect to what it implies about our views and positions.
In a nutshell
- The Problem: Infection with soil-transmitted helminths (STHs) can cause chronic pain and malnurition, reducing school performance and productivity. For more background on STH (symptoms, consequences, and global prevalence), click here.
- The Program: Mass drug administration at regular intervals to entire high-risk populations, aiming to reduce STH infection rates to low enough levels so that damaging symptoms are eliminated. This program is often, but not always, combined with the use of praziquantel (PZQ) to control schistosomiasis, another parasite infection. For information on the combination program, click here.
- Track record: Experimental evaluations of this program have had mixed results - for example, it has resulted in slight weight gain in some cases but not in others. The combination program of STH drugs and prazinquatel has a stronger track record (more here).
- Cost-effectiveness: Estimates imply that this is among the most cost-effective interventions.
- Bottom line: Use of STH drugs alone is not strongly recommended. The combination program of STH drugs and prazinquatel is more promising (more here).
- Basics of the program
- Program track record
- Recommendations and concerns
Basics of the program
What is the program? What problem does it target?
Anthelmintic drugs are recommended (by the World Health Organization) for control of soil-transmitted helminths,1 a class of parasites that can cause pain and malnutrition (more on soil-transmitted helminths here). Treatment is recommended 2-3 times per year in areas of intense transmission, and annually in areas of lower transmission intensity.2
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 as efficiently as possible.
Anthelmintic drugs: may be donated by manufacturers in some cases. GlaxoSmithKline, the manufacturer of albendazole, donates significant amounts of it free of charge3, although it stresses the role of this drug in combating a different disease (lymphatic filariasis, which we report on here) and it's unclear whether it makes albendazole available specifically for the purposes described here.
Distribution mechanism: the Disease Control Priorities Report states that schools provide a strong infrastructure and that teachers can be trained to deliver drugs safely.4 In the absence of training, mobile teams can come in to implement drug administration, but this method can cost significantly more.5
Program track record
Micro evidence: Has this program been rigorously evaluated and shown to work?
A recent review finds 34 high-quality evaluations of anthelmintic drugs' effects on various health and well-being measures including weight and school attendance and performance. This study concluded, "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 beneï¬t here. Two trials looked at adverse events, but the trials were small. Further research is needed." The full review presents the results of each of the trials.6
The Disease Control Priorities report has a more optimistic take on the available evidence, asserting that anthelmintics of the kind discussed here have been associated with positive effects on outcomes including nutritional status, cognitive development, and infant survival.7 However, the review cited above is more recent, appears more comprehensive, and lays out its full criteria, sources and results (unlike the Disease Control Priorities report).
Note that a fairly well-known evaluation of combination drug treatment (both anthelmintics of the kind discussed here and prazinquatel for schistosomiasis control, discussed here) found positive effects on school attendance.8 More on our interpretation of "micro evidence" and evaluation quality here.
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" here.
Recommendations and concerns
Do expert reviews of the comparative merits of interventions endorse this one?
See this page for sources consulted.
None of our sources strongly endorse the exact intervention discussed here (use of drugs targeted only at soil-transmitted helminths). One (listed first) gives a conditional recommendation.
- Disease Control Priorities 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] ... in the developing world."9
- Copenhagen Consensus. Endorses a combination deworming program, involving both the drugs discussed here and a different drug to combat schistosomiasis (see this separate report).
- Disease priorities paper by Jamison et al.. Does not include treatment for STHs on its list of 7 cost-effective interventions.10
What are the potential downsides of the intervention?
- Repeated MDA treatment is required, and there is a potential for drug resistance to develop.11
- The DCP report says in several places that deworming is safe,12 which is one reason that application at a population level is justified (no safety concerns for the non-infected who are treated), yet in the conclusion says safety is an area for further research.13
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 infection suspicion are treated.14
Population deworming (MDA treatment for all people in an area of high infection) is recommended by the World Health Organization.15 However, treating school-aged children as a targeted population group is the version that has been most closely evaluated.16 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.17
What is the cost-effectiveness of this intervention?
- Cost per person treated for STH has been estimated as ranging between $0.03 and $0.51 for school-based interventions.18
- Cost per DALY averted (more on the DALY metric here): approximately $3.41.19 This would make STH treatment one of the most cost-effective interventions.20
- Disease Control Priories Project. 2006. "Disease Control Priorities in Developing Countries (2nd Edition)." Available online at http://dcp2.org/pubs/DCP, accessed 7/9/09.
- GlaxoSmithKline. 2009. "Eliminating lymphatic filariasis." Online at http://www.gsk.com/infocus/eliminating.htm, accessed 7/9/09.
- Jamison, D., P. Jha, and D. Bloom. 2008. "Copenhagen Consensus 2008 Challenge Paper: Diseases." Available online at http://www.copenhagenconsensus.com/Files/Filer/CC08/Papers/0%20Challenge..., accessed 7/9/09.
- Miguel, Edward, and Michael Kremer. 2004. "Worms: Identifying Impacts on Education and Health in the Presence of Treatment Externalities." Econometrica 72:1, 159–217. Available online at "http://weber.ucsd.edu/~tkousser/Miguel and Kremer.pdf", accessed 7/9/09.
- Taylor-Robinson, D.C., A.P. Jones, and P. Garner. 2007. "Deworming drugs for treating soil-transmitted intestinal worms in children: effects on growth and school performance." Cochrane Database of Systematic Reviews. Summary available online at http://www.cochrane.org/reviews/en/ab000371.html, accessed 7/9/09.
"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)." DCP 2006, Pgs 472-3.
"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)" DCP 2006, Pg 473.
"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." DCP 2006, Pg 473.
"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)." DCP 2006, Pg 475.
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 signiï¬cant 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 2007, Pg 2.
DCP 2006, pg 474.
DCP 2006, Pg 480.
Jamison 2008, Pg 51.
"Obstacles that diminish the effectiveness of periodic deworming are the low efficacy of single-dose mebendazole and albendazole for the treatment of hookworm and trichuriasis, respectively (Adams and others 2004; Albonico and others 1994); high rates of posttreatment reinfection for STHs in areas of high endemicity (Albonico and others 1995); and diminished efficacy with frequent and repeated use (Albonico and others 2003), possibly because of anthelmintic resistance (see the section "Research and Development")." DCP 2006, Pg 472.
"The BZAs and PZQ are inexpensive; they have undergone extensive safety testing and have been used by millions of individuals with only a few minor side effects." DCP 2006, Pg 473.
"The advantage of periodic deworming lies in its simplicity (one tablet per child) and safety." DCP 2006, Pg 474
DCP 2006, Pg 479.
"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." DCP, 2006 Pg 472.
"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." DCP 2007, Pg 473.
"Several studies have evaluated the costs of school-based periodic deworming in several different settings, whereas comparable studies on other interventions are still lacking." DCP 2006, Pg 474.
"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)." DCP 2006, Pg 473.
"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)." DCP 2006, Pg 474.
"For a population of 1 million people in low- and middle-income countries, if treatment is limited to school-age children treated 1.1 times per year with albendazole and then reinfected, the cost per DALY averted is estimated at US$3.41 for STH infections. That is, if spending were capped at US$1 million, total DALYs would be reduced by nearly 300,000." DCP 2006, Pg 476.
See DCP 2006, Pgs 41-42, Figures 2.2 and 2.3 for a chart of the cost-effectiveness range (measured in cost per DALY) for many programs.