Preventive chemotherapy in human helminthiasis: theoretical and operational aspects.

Preventive chemotherapy (PC), the large-scale distribution of anthelminthic drugs to population groups at risk, is the core intervention recommended by the WHO for reducing morbidity and transmission of the four main helminth infections, namely lymphatic filariasis, onchocerciasis, schistosomiasis and soil-transmitted helminthiasis. The strategy is widely implemented worldwide but its general theoretical foundations have not been described so far in a comprehensive and cohesive manner. Starting from the information available on the biological and epidemiological characteristics of helminth infections, as well as from the experience generated by disease control and elimination interventions across the world, we extrapolate the fundamentals and synthesise the principles that regulate PC and justify its implementation as a sound and essential public health intervention. The outline of the theoretical aspects of PC contributes to a thorough understanding of the different facets of this strategy and helps comprehend opportunities and limits of control and elimination interventions directed against helminth infections.

Soil-transmitted nematode infections and mebendazole treatment in Mafia Island schoolchildren.

In August 2000, a cross-sectional study was performed to assess the prevalence and intensity of soil-transmitted nematode infections in schoolchildren on Mafia Island. Hookworm infection was widespread (72.5% prevalence) whereas Trichuris trichiura was less prevalent (39.7%) and Ascaris lumbricoides was present at a low prevalence (4.2%), mainly in urban areas. In a subsample of the study population, both Necator americanus and Ancylostoma duodenale were found, although N. americanus was more prevalent. This survey was followed by a parasitological evaluation of mebendazole treatment using a single, 500-mg dose. The data on outcome were used for comparison with those from recent studies of similar treatment regimens in the neighbouring island of Pemba, Zanzibar, where periodic chemotherapy with mebendazole to schoolchildren has been implemented as part of a helminth-control programme since 1994. A higher efficacy of mebendazole against hookworm infection was found in Mafia Island (where a cure 'rate' of 31.3% and an egg-reduction 'rate' of 78.1% were recorded) when compared with that observed in Pemba Island, possibly indicating that hookworms may be developing mebendazole resistance on Pemba Island as a result of intense exposure to the drug there.

Effects of iron supplementation and anthelmintic treatment on motor and language development of preschool children in Zanzibar: double blind, placebo controlled study.

OBJECTIVE: To measure the effects of iron supplementation and anthelmintic treatment on iron status, anaemia, growth, morbidity, and development of children aged 6-59 months. DESIGN: Double blind, placebo controlled randomised factorial trial of iron supplementation and anthelmintic treatment. SETTING: Community in Pemba Island, Zanzibar. PARTICIPANTS: 614 preschool children aged 6-59 months. MAIN OUTCOME MEASURES: Development of language and motor skills assessed by parental interview before and after treatment in age appropriate subgroups. RESULTS: Before intervention, anaemia was prevalent and severe, and geohelminth infections were prevalent and light-Plasmodium falciparum infection was nearly universal. Iron supplementation significantly improved iron status, but not haemoglobin status. Iron supplementation improved language development by 0.8 (95% confidence interval 0.2 to 1.4) points on the 20 point scale. Iron supplementation also improved motor development, but this effect was modified by baseline haemoglobin concentrations (P=0.015 for interaction term) and was apparent only in children with baseline haemoglobin concentrations <90 g/l. In children with a baseline haemoglobin concentration of 68 g/l (one standard deviation below the mean value), iron treatment increased scores by 1.1 (0.1 to 2.1) points on the 18 point motor scale. Mebendazole significantly reduced the number and severity of infections caused by Ascaris lumbricoides and Trichuris trichiura, but not by hookworms. Mebendazole increased development scores by 0.4 (-0.3 to 1.1) points on the motor scale and 0.3 (-0.3 to 0.9) points on the language scale. CONCLUSIONS: Iron supplementation improved motor and language development of preschool children in rural Africa. The effects of iron on motor development were limited to children with more severe anaemia (baseline haemoglobin concentration <90 g/l). Mebendazole had a positive effect on motor and language development, but this was not statistically significant.

Epidemiology of iron deficiency anemia in Zanzibari schoolchildren: the importance of hookworms.

Anemia is estimated to affect one-half of school-age children in developing countries. The school years are an opportune time to intervene, and interventions must be based on sound epidemiologic understanding of the problem in this age group. We report on the distribution of iron deficiency and anemia across age, sex, anthropometric indexes, and parasitic infections in a representative sample of 3595 schoolchildren from Pemba Island, Zanzibar. Iron status was assessed by hemoglobin, erythrocyte protoporphyrin (EP), and serum ferritin concentrations from a venous blood sample. Overall, 62.3% of children were anemic (hemoglobin < 110 g/L), and 82.7% of anemia was associated with iron deficiency. The overall prevalence of iron-deficient erythropoiesis (EP > 90 mumol/mol heme) was 48.5%, and the prevalence of exhausted iron stores (serum ferritin < 12 micrograms/L) was 41.3%. In bivariate analyses, iron status was slightly better in girls than in boys, and was better in children aged 7-11 y than in those older or younger. Hemoglobin but not EP or serum ferritin concentrations were lower in stunted children. Infection with malaria, Trichuris trichiura, Ascaris lumbricoides, and hookworms were all associated with worse iron status; the association with hookworms was strongest by far. In multivariate analyses, hookworm infection intensity was the strongest explanatory variable for hemoglobin, EP, and serum ferritin. Sex, malarial parasitemia, A. lumbricoides infection, and stunting were also retained in the multivariate model for hemoglobin. Twenty-five percent of all anemia, 35% of iron deficiency anemia, and 73% of severe anemia were attributable to hookworm infection; < 10% of anemia was attributable to A. lumbricoides, malaria infection, or stunting. We conclude that anthelminthic therapy is an essential component of anemia control in schoolchildren in whom hookworms are endemic, and should be complemented with school-based iron supplementation.

[Intestinal parasitic infections and schistosomiasis in the valley of the Senegal river in the Islamic Republic of Mauritania]. / Parasitoses intestinales et schistosomiases dans la vallée du fleuve Sénégal en République Islamique de Mauritanie.

An epidemiological survey was carried out in the Trarza and Brakna regions of the Senegal River valley in Mauritania prior to implementation of a program to control intestinal parasitic infection and schistosomiasis. A total of 1297 school children between the ages of 5 and 12 years from a randomized selection of villages in the region were examined to determine the prevalence and intensity of intestinal parasitic infections and schistosomiasis. Overall prevalence was 38.1% for intestinal parasitic infection, 7.1% for intestinal schistosomiasis, and 17.1% for urinary schistosomiasis. Analysis of weight and height as indicators of nutritional status indicated that 40.9% of the children examined were under the 10th percentile of the weight-for-height indicator and that there was a statistically significant correlation between malnutrition, diarrhea, and intestinal parasitic infection (p < 0.0001). Measurement of hemoglobin levels showed that 50.4% of children were anemic (hemoglobin level < 11 g/dl) and that there was a correlation between anemia and infection by Schistosoma haematobium. This is the first epidemiological survey on intestinal parasitic infections in Mauritania and the first study on Schistosoma mansoni on the Mauritanian side of the Senegal River. Findings suggest not only that implementation of a program to control intestinal parasitic infection and schistosomiasis is needed in the region but also that it should be associated with a food/iron supplementation program and growth monitoring.