Metrifonate in the Control of Urinary Schistosomiasis in Zanzibar

Introduction Advances in diagnostic techniques and chemotherapy now ensure that reduction in disease due to schistosomiasis is within the capabilities of the current health infrastructures of many endemic countries [1]. The effectiveness of metrifonate, and organo-phosphorus compound with specific anticholinesterase activity against Schistosoma haematobium, has recently been reviewed [2]. Its relatively low cost, lack of toxicity, and high efficacy make it an attractive option for large-scale treatment. However, most of the published studies on the efficacy of metrifonate for S. haematobium control have been limited to small groups of school-age children; this age group usually has the highest prevalence and the heaviest infections [3, 4]. Some studies have examined the efficacy of varying doses of metrifonate; others have used a single dose of 10 mg/kg body weight and achieved a reduction in egg output of at least 90% [4-6]. A few studies have utilized the WHO-recommended schedule of three doses of 7.5 mg/kg body weight at two-week intervals and achieved a similar reduction in egg count [7, 8]. Zanzibar, an island off of the eastern coast of Tanzania, was recognized as a highly endemic area of urinary schistosomiasis as early as 1885 [9]. It was the site of the first clinical trials of metrifonate against S. haematobium infection 15 years before this present study [10, 11]. This paper describes the results of selective population chemotherapy in an entire community in northern Zanzibar island. Metrifonate was administered in three doses (7.5 mg/kg body weight each time) at intervals of two weeks. The operational aim of the study was to (1) reduce the prevalence of heavy infections (defined as [is greater than of equal to] 50 eggs per 10 ml of urine) by 75% in two years, and (2) reduce the overall prevalence of infection by 50% in two years. The effects of treatment, according to age group, sex, and initial intensity of infection were observed, and the efficacies of comple (three doses) treatment and incomplete treatment were compared. Methods Kinyasini district in Zanzibar, United Republic of Tanzania, was selected as the study are. A detailed map (Fig. 1) showing the location of all houses in the district, as well as other relevant geographic features, was prepared and a complete census was undertaken in May 1981. All the residents in the district, who produced urine, were included in the study, each one being assigned a serial number. The four surveys in the study were carried out during a two-year period (July 1981 to July 1983), the census being updated at each survey. The examination and treatment team was composed of a health officer, two assistant health officers, three microscopists, two laboratory assistants and a driver, all from the Ministry of Health. The presence of S, haematobium infection was detected in a spicemen of urine collected from each person. When the urine specimens were brought to the examination team, few drops of 10% formaldehyde were added. Using the Nytrel syringe filtration technique, a 10 ml random aliquot of each well-mixed specimen was examined by a trained microscopist either in a field laboratory or in the central laboratory. Either new or adequately washed Nytrel filters were used at each survey. No quality control was performed during the examinations. If a person was found to be positive, i.e., anyone with at least a single S. haematobium egg in the urine, treatment was given based on the WHO-recommended regimen (3 doses of 7.5 mg of metrifonate per kg body weight at 2-week intervals) [1]. At each survey, the data on each individual included the district, school, house number, family order number, age, six, urinary egg count, date of examination, weight, number of tablets of metrifonate per dose, and the number of doses received. Preliminary data check and analysis using hand calculators were completed by the project staff. …