Parasitic worms are debilitating, widespread, and under-treated. School-based deworming is safe, cost-effective and scale-able. What is the evidence base for the work that the Deworm the World Initiative undertakes?
We summarize the evidence base for mass school-based deworming programs in this post. Here are key findings across the key impacts of deworming: school participation, future earnings, and cognition and nutrition.
- Bleakley’s study of a deworming campaign in the U.S. South in the 1910s estimated that an infected child would have been 20 percentage points less likely to be enrolled in school than a non-infected child, and was also 13 percentage points less likely to be literate.
Miguel and Kremer’s experimental evaluation in Western Kenya found a 25% reduction in student absenteeism at treatment schools.
Baird and colleagues’ long-run study based on the Western Kenya deworming finds that among females, deworming increased the rate of passing the national primary school exit exam by 9.5 percentage points on a base of 41%.
- Hookworm infections could have explained as much as 22% of the income gap between the U.S. North and South.
- In Kenya, men who were treated as children worked 3.4 more hours per week, spent more time in entrepreneurial activities, and were more likely to work in higher-wage manufacturing jobs. This long-term impact study in Kenya calculates a rate of return for governments who invest in deworming of 32-52%.
Nutrition and Cognition
“Does Mass Deworming Affect Child Nutrition?: Meta-analysis, Cost-Effectiveness, and Statistical Power” authored by Kevin Croke, Joan Hamory Hicks, Eric Hsu, Michael Kremer, and Edward Miguel, finds a “substantial” and “highly robust” positive effect on child weight resulting from deworming. The effects are particularly large in areas above 20% prevalence; this is the same threshold at which the WHO currently recommends mass treatment. The authors also note the cost-effectiveness of deworming, with "the estimated average weight gain per dollar expenditure from deworming...more than 35 times that from school feeding programs as estimated in RCTs."
A randomized health intervention that provided iron, Vitamin A and deworming drugs to Indian preschool children in poor areas of Delhi found a significant gain in child weight and school participation compared to intervention with Vitamin A alone. Absenteeism was reduced by one-fifth in the treatment group. We do note, however, that the large DEVTA trial found no impacts of deworming or Vitamin A supplementation on mortality in a rural area where worm loads were light. We prioritize, and urge our government partners to prioritize, investment in areas where worm loads are high.
A randomized controlled trial in Uganda (Alderman and colleagues, 2006) finds that the provision of periodic anthelmintic treatment as a part of child health services resulted in an increase in weight gain of about 10% above expected weight gain when treatments were given twice a year, and an increase of 5% when the treatment was given annually.
Chronic infections in childhood (from diarrhea, to malaria, to worms) generate inflammatory (immune defense) responses lead substantial energy to be diverted from growth. There are interaction effects too, with deworming, for example, making it easier to fight off malaria. More generally, in their summary of deworming, the WHO points to several channels by which worms may impair nutrition, and notes several studies that can support these claims.
- Owen Ozier’s study on the long-term effects of early childhood deworming suggests that reduced exposure to worm infections may improve cognition for children less than one year of age. These young children in the catchment area of treatment schools showed large gains on cognitive tests about ten years later.
Is mass treatment justified? On cost-effectiveness grounds we believe that it clearly is, as the cost of treatment is cheaper than individual screening. The WHO states that the cost of screening is four to ten times that of the treatment itself. Because the drugs are very safe and has no side effects for the uninfected, the WHO does not recommend individual screening. The WHO instead recommends mass drug administration in areas where more than 20% of children are infected.
Deworming through schools, and preschools in some areas, provides the greatest opportunity to reach a high proportion of the at-risk population while minimizing costs through the use of existing government infrastructure.