Date Published: January 27, 2009
Publisher: Public Library of Science
Author(s): David Taylor-Robinson, Ashley Jones, Paul Garner, Gavin Yamey
Partial Text: The World Bank ranks soil-transmitted helminth infection as causing more ill health in children aged 5–15 years than any other infection. In light of this ranking, global agencies recommend regular, mass treatment with deworming drugs to children in developing countries ,. The World Health Organization (WHO) argues that “deworming helps meet the Millennium Development Goals” , in particular the six health-related goals: (1) eradicate extreme poverty and hunger; (2) achieve universal primary education; (3) promote gender equality and empower women; (4 and 5) reduce child mortality and improve maternal health; and (6) combat HIV/AIDS, malaria, and other diseases (http://www.un.org/millenniumgoals). However, deworming campaigns cost money to deliver, and so we must be clear that WHO statements about the impact of these programmes are based on reliable evidence.
Our objectives were to summarize the effects of deworming drugs used to treat soil-transmitted intestinal worms on two outcomes: growth and school performance in children. The inclusion criteria were RCTs and quasi-randomised controlled trials that evaluated these outcomes. A total of 34 trials were included, including ten new trials since the 2000 review. Six trials in the 2000 review were excluded from the updated systematic review, as our methods of applying inclusion criteria have become more exacting —for instance, trials with only two units of allocation, and trials that ignored randomisation in the analysis were excluded in the updated review.
Deworming drugs are associated with increases in weight after a single dose. Generally, there remains no significant difference detected in multiple dose trials, apart from the cluster RCT in schools in Zanzibar ,; more recent cluster RCTs looking for an effect on weight gain have failed to demonstrate a difference. For school performance, data were very limited, and no convincing treatment effect was demonstrated. If benefit is not shown in RCTs, then it seems benefit is even less likely in “real world” operational conditions. A reasonable interpretation of the newly updated systematic review may be that deworming drugs used in targeted community programmes may be effective in relation to weight gain in the short term in some circumstances, but not in others; the potential long-term impact has not been demonstrated conclusively.
With obvious relationships between worm infection, health status, and poverty, randomised trials help differentiate causality from confounding. Gulani and colleagues’ systematic review of intestinal anthelmintic drugs on anaemia shows a marginal impact on haemoglobin, and the authors say that this could translate into a small effect on anaemia in populations where worms are common . Our updated systematic review shows improvements in weight after one dose of deworming, but generally not in trials with longer follow-up, and no evidence of effect on school performance. Thus, there is a mismatch between the state of reliable, direct evidence of benefit and the benefit claimed by advocates of deworming.