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

Abstract

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 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.