Associations among multiple geohelminth species infections in schoolchildren from Pemba Island.

In order to estimate the potential benefits of interventions against multiple geohelminth species in endemic areas, an improved understanding of the population biology of multiple infections is required. This paper presents a detailed analysis of the associations among Ascaris lumbricoides, Trichuris trichiura and hookworm infections in 1539 schoolchildren on Pemba Island, Tanzania, where 58% of the sampled children carried infections of all 3 parasites at the time of the study. Infection intensities of different species were positively correlated, and individuals with single-species infections had generally lower species-specific egg counts than individuals with multiple-species infections. There was no age- or sex-related clustering of infections. A weak clustering of intense infections among individuals with multiple-species infections was observed, which became more pronounced as the threshold defining an intense infection increased for each species. The results suggest that individuals with multiple species infections are likely to be at highest risk of geohelminth-related morbidity, not only because of the number of infections they harbour, but also because they generally carry heavier infections of each species.

Parasitic infections in Pemba Island school children.

Intestinal helminths, schistosomiasis and malaria have been recognised for decades to be major public health problems in Zanzibar, Tanzania. During the evaluation of the impact of the Zanzibar Helminth Control Programme, baseline parasitological data on 3,605 school children were collected in Pemba Island. Prevalence of intestinal helminth infections was 72%, 94% and 96% for Ascaris lumbricoides, Trichuris trichiura and hookworm, respectively. Thirty one percent of children tested positive for haematuria, a reliable indicator of urinary schistosomiasis in the study area. Malaria parasites were found in 61% of children. Hookworm infections and haematuria were more prevalent in boys. Sixty seven percent of the children were infected with all the three helminths, and 28% harboured double infection. No association was found between intestinal helminths and schistosomiasis or malaria. Children living in rural areas were more heavily infected with hookworms, schistosomiasis and malaria compared to children in towns. Results from this study provided relevant information for designing a "plan of action" for the integrated control of filariasis, intestinal helminths, malaria and schistosomiasis in Zanzibar.

Control of Schistosoma haematobium morbidity on Pemba Island: validity and efficiency of indirect screening tests.

Four indirect screening methods for the detection of Schistosoma haematobium morbidity are compared (history of haematuria, visual haematuria, and microhaematuria at the 1+ and 2+ positivity limit by reagent strips) in terms of their diagnostic performance under conditions of progressive decrease in prevalence of infection, intensity and risk of morbidity as a result of repeated schistosomiasis control programmes on Pemba Island, United Republic of Tanzania. The results show that the sensitivity of a history of haematuria was higher (71%) in children but lower in adults (40%), similar to the findings for visual haematuria in children (60%) and adults (40%) at baseline. However, visual haematuria had a higher specificity, positive predictive value, and efficiency than a history of haematuria in both children and adults. Microhaematuria at the 1+ positivity limit (by reagent strips) had the highest sensitivity of all the methods investigated, but the lowest specificity, positive predictive value, and efficiency. Quantitatively, the indirect methods tended to increase in specificity, negative predictive value, and efficiency during the course of the intervention programme. In contrast, positive predictive value tended to decrease, while the sensitivity remained fairly stable. Overall, these findings suggest that a history of haematuria and/or visual haematuria are appropriate methods for preliminary screening of communities to identify those at risk of morbidity. Thereafter, microhaematuria (1+ positivity limit) may be the more appropriate method for targeting intervention at the individual level.

The relationship between prevalence of Schistosoma haematobium infection and different morbidity indicators during the course of a control programme on Pemba Island.

A long-term schistosomiasis control programme was initiated on Pemba Island, Tanzania in 1986 with the aim of eliminating morbidity due to Schistosoma haematobium infection. The programme used haematuria as a community indicator of morbidity for surveillance and for identifying individuals for selective population chemotherapy. Analysis of the first 3 evaluation studies showed that the prevalence of microhaematuria was linearly related to the prevalence of infection, and that visually detectable haematuria was a marker of the intensity of infection and risk of morbidity in a community. These relationships remained consistent during repeated community-based chemotherapy, suggesting that measures of haematuria may be useful tools for surveillance.

Rate of reinfection with intestinal nematodes after treatment of children with mebendazole or albendazole in a highly endemic area.

The comparative efficacy of albendazole and mebendazole in the treatment of intestinal nematode infections were compared 3 weeks after treatment in a randomized trial among schoolchildren on Pemba Island, Tanzania. Egg counts were compared 3 weeks, 4 months and 6 months after treatment of 731 children seen on each occasion. Differences in the efficacies were apparent with some nematodes 21 d after treatment, but these were no longer apparent 4 months after treatment, and by 6 months intensities of infection were similar to pre-treatment levels. These findings suggest that treatment of schoolchildren every 4 months may be necessary in this highly endemic area in order to have an impact on the intensity of intestinal nematode infections sufficient to be likely to reduce morbidity.

Evolution of operational research studies and development of a national control strategy against intestinal helminths in Pemba Island, 1988-92.

Intestinal helminthic infections in Pemba Island, United Republic of Tanzania, have been perceived as a public health problem for many decades. School surveys in 1988 and 1992 and a community survey in 1991 were carried out to assess the distribution of prevalence and the intensity of these infections and to define the most effective strategy for control. The prevalence of helminthic infections exceeded 85% in all the surveys, and intensity was moderate. These studies identified the high-risk age groups, high transmission areas for different parasites, and the most cost-effective anthelminthic drug. This work is an example of how existing health systems and simple analytical tools may be used to generate useful data which, in turn, are used to define suitable intervention strategies. As a result, the Ministry of Health of Zanzibar has developed a national plan for the integrated control of intestinal helminths. This plan envisages periodic mass treatment of school-age children with mebendazole (500 mg, single dose, every four months) for the control of morbidity due to Ascaris, Trichuris, and hookworms.

A randomized controlled trial comparing mebendazole and albendazole against Ascaris, Trichuris and hookworm infections.

The efficacies and side effects of single dose treatments with 500 mg mebendazole (Janssen Pharmaceutica) and 400 mg albendazole (SmithKline Beecham) against intestinal nematodes were compared in a single-blind, randomized controlled trial among 2294 children aged 6 to 12 years on Pemba Island, Zanzibar, among whom infections with Ascaris, hookworms and Trichuris were highly prevalent. Both drugs were highly effective against Ascaris, with cure rates of over 97%. The cure rates for Trichuris were low, but mebendazole was significantly better than albendazole and produced a greater reduction in the geometric mean egg count. Mebendazole was inferior to albendazole in curing hookworm infections and in reducing the geometric mean egg count. There was no difference in the frequency of side effects reported by heavily infected children treated with either drug. In a trial on 402 children, 500 mg mebendazole (Janssen) was compared with a generic version of the drug, 500 mg mebendazole (Pharmamed). No difference was apparent in the efficacies of the 2 treatments against any of the 3 parasites studied.

Efficacy of a single dose of mebendazole on prevalence and intensity of soil-transmitted nematodes in Zanzibar.

The efficacy of a single-dose of mebendazole to treat intestinal helminths was studied in Pemba Island, Zanzibar, with the view of incorporating it in future control programmes. A single Kato-Katz stool examination was performed on 2,269 individuals from all age groups. 1,883 individuals were treated with 500 mg of mebendazole (250 mg for children below two years) and re-examined one month and four months after therapy. A total of 466 presented themselves for all three surveys and the data has been reported in this study. The overall cure rate for ascariasis was 93.2% and reduction of egg load after treatment was 89.8% in persistent positive cases. Although the cure rates were lower in trichuriasis (25.6%) and hookworm (17.8%) infections, egg reduction was more evident with 47% for Trichuris trichiura and 51.9% for hookworms. A single dose of mebendazole results not only in a high cure rate for ascariasis but also in a decrease in intensity of ascariasis, trichuriasis and hookworm infections, thereby contributing to its incorporation into low-budget control programmes in developing countries.