The impact of zinc supplementation on Schistosoma mansoni reinfection rate and intensities: A randomized, controlled trial among rural Zimbabwean schoolchildren H Friis 1,3 , P Ndhlovu 2 , T Mduluza 2 , K Kaondera 2 , B Sandstro ¨m 3 , KF Michaelsen 3 , BJ Vennervald 1 and NO Christensen 1 1 Danish Bilharziasis Laboratory, Denmark; 2 Blair Research Laboratory, Ministry of Health, Zimbabwe; and 3 Research Department of Human Nutrition, Royal Veterinary and Agricultural University, Denmark Objectives: To assess the effect of zinc supplementation on susceptibility to S. mansoni reinfections among schoolchildren. Design: Randomized, double-blind, placebo-controlled trial. Setting and Subjects: 313 rural Zimbabwean schoolchildren (144 boys and 169 girls), 11–17 y). Interventions: Supplementation with zinc (30 or 50 mg) or placebo on schooldays for 12 months. Due to drought, a food programme was in operation during the last eight months of the study. Outcome measures: S. mansoni and S. haematobium reinfection rates and intensities. Results: There was no difference in reinfection rates between the zinc and placebo groups (25 vs 29%, P 0.46). However, the median intensity of S. mansoni reinfection, although low in both groups, was significantly lower in the zinc than in the placebo group (7 vs 13 eggs per gram of faeces, P 0.048). No difference in either S. haematobium reinfection rates or intensities were seen. Conclusions: Zinc supplementation reduced the intensity of S. mansoni reinfections. Although the intensities of reinfection were very low, the finding probably reflects a biological effect of zinc that could be of public health importance in settings with higher transmission. Sponsorship: Danish International Development Assistance. Descriptors: Randomized, controlled trial; zinc deficiency; zinc supplementation; S. mansoni; S. haematobium; reinfection; schoolchildren; Zimbabwe Introduction Interactions of nutrition and infection have received con- siderable interest for many years (Scrimshaw et al, 1968). While most infections have the potential to impair the nutritional status of the host, single nutrient deficiencies may either aggravate or alleviate a specific infection (Scrimshaw et al, 1968). Accordingly, repletion of single nutrient deficiencies may either hinder or facilitate control of a specific infection, for which reason knowledge about the synergistic or antagonistic nature of such interactions is important prior to commencement of food or single nutrient supplementation programmes. The effects of micronutrient deficiencies on susceptibil- ity to specific infections have recently been focused on (Bundy et al, 1987; Tomkins et al, 1989). In particular, zinc deficiency could be of importance for susceptibility to infections, since it is essential for numerous immunefunc- tions (Gross et al, 1980; Beisel, 1982) and may affect parasite kinetics (Bundy et al, 1987). However, studies are impeded by the lack of a satisfactory measure of zinc status. In order to assess the role of zinc deficiency in suscept- ibility to S. mansoni infections, a randomized controlled zinc supplementation trial, based on the classic schistoso- miasis reinfection study, was carried out among a study population in rural Zimbabwe with growth-limiting zinc deficiency (Friis, 1996). Subjects and methods Study area and population A subsistence farming community in Sabi Valley, 65 km east of Chiredzi in south-eastern Zimbabwe, with low nutritional status and high prevalence of S. mansoni infec- tion among schoolchildren, was identified. The climate in the area was hot and dry, with an annual rainfall below 400 mm, and the vegetation dry savanna woodland and scrub. The staple crops were maize and millet. Cattle and goats were kept, but mainly used as cash products. The Mkwasini River, a tributary of the Save River, courses between Mareya and Muteo Primary Schools, from which subjects were recruited for this study. Children attending grade three to six were eligible for inclusion in the study. Accordingly, 198 (84.3%) of 235 and 115 (92.0%) of 125 children from grade three to six at Muteo and Mareya Primary School, respectively, were included in the study. Correspondence: Dr H Friis, c/o Danish Bilharziasis Laboratory, Jaegersborg Alle ´ 1D, DK-2920 Charlottenlund, Denmark. Received 10 February 1996; revised 11 September 1996; accepted 1 October 1996