A review and meta-analysis of the impact of intestinal worms on child growth and nutrition

Table of Contents
Summary	119
1. Introduction	119
1.1 The gastrointestinal ecosystem	119
1.2 Groups of intestinal parasitic worms that infect humans	121
1.2.1 Flukes or trematodes	121
1.2.2 Tapeworms or cestodes	122
1.2.3 Roundworms or nematodes	123
1.3 How worms may affect human nutrition and growth	126
1.4 Design of studies estimating the impact of worms	128
1.5 Aims	128
2. Factors affecting the impact of intestinal worms	128
2.1 Species of intestinal worm	128
2.2 Prevalence of infection	129
2.3 Number and distribution of worms	132
2.4 Duration of infection	135
2.5 Rate of reinfection	135
2.6 Summary	136
3. Factors affecting the impact of treatment	137
3.1 Study design: controls and randomization	138
3.2 Anthelmintic drugs	138
3.3 Intervals between treatments	141
3.4 Duration of follow-up	142
3.5 Outcomes measured and the need for controls	142
3.6 Initial nutritional status	143
3.7 Age of subjects	144
3.8 Remedial therapy after treatment	144
3.9 Summary	145
4. Aims and methods of the meta-analysis	145
4.1 Search terms	145
4.2 Inclusion criteria	146
4.3 Exclusion criteria	147
4.4 Meta-analysis	147
5. Results of the meta-analysis	147
5.1 Geographic origin of studies	150
5.2 Estimates of effects	150
5.3 The figures and how to interpret them	150
5.4 Sources of error or bias	150
6. Discussion	153
6.1 Magnitude of effects	153
6.2 Treatment alone is not enough	159
6.3 The Cochrane Collaboration Review	161
6.4 Characteristics of an ideal study	162
6.5 Implications for programmes	163
6.6 Conclusions	166
Acknowledgements	167
References	167
Appendix: Summary of papers identified for the review	177

Summary

More than a half of the world's population are infected with one or more species of intestinal worms of which the nematodes Ascaris lumbricoides, Trichuris trichiura and the hookworms are the most common and important in terms of child health. This paper: (1) introduces the main species of intestinal worms with particular attention to intestinal nematodes; (2) examines how such worms may affect child growth and nutrition; (3) reviews the biological and epidemiological factors that influence the effects that worms can have on the growth and nutrition of children; (4) considers the many factors that can affect the impact of treatment with anthelmintic drugs; (5) presents the results of a meta-analysis of studies of the effect of treating worm infections on child growth and nutrition; (6) discusses the results in terms of what is reasonable to expect that deworming alone can achieve; (7) describes some important characteristics of an ideal study of the effects of deworming; and (8) comments on the implications for programmes of recommendations concerning mass deworming.