Bancroftian filariasis on Pemba Island, Zanzibar, Tanzania: an update on the status in urban and semi-urban communities.

Cross-sectional clinical, parasitological and entomological surveys for bancroftian filariasis were conducted in Konde, Chake Chake and Kengeja, three urban and semiurban communities on Pemba Island, and the results were compared with similar surveys done 15 years earlier. The overall prevalences of clinical manifestations among males aged 15 years or more (n = 614) was remarkably similar to those recorded 15 years earlier: elephantiasis 1.4% in 1975 and 1.1% in 1990; hydrocele, 22.4% and 21.8%, respectively. However, when the communities were compared individually, there was a reduction in the hydrocele prevalence in Konde from 22.4% to 11.5% and an increase in Kengeja from 27.0% to 35.5%. The overall microfilarial prevalence found during night blood surveys of all individuals aged 1 year or more (n = 2687) was 9.7%, compared to 14.2% recorded in 1975. The reduction was most pronounced in Konde. Of 1052 female mosquitoes caught with CDC light traps, 95% were Culex quinquefasciatus and 5% Anopheles gambiae s.l. Infective larvae of Wuchereria bancrofti were found only in the former. The filariasis situation in urban and semiurban communities on Pemba Island appears not to have changed considerably over the last 15 years.

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.

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.

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.

Control of morbidity due to Schistosoma haematobium on Pemba Island: egg excretion and hematuria as indicators of infection.

The variability of Schistosoma haematobium egg excretion using a quantitative syringe filtration technique and the variability of hematuria detected visually and by reagent strips were studied in a population of 520 subjects from the village of Pujini (Pemba Island, Zanzibar, Tanzania) for 6 consecutive days. A high degree of day-to-day variability of egg excretion within subjects was found both in the whole population and in the 5-19 year age group. Subjects with 1 urinary egg count of greater than or equal to 50 eggs/10 ml urine were not similarly classified in 36-61% of the other 5 examinations and 4-16% of their other examinations were negative. Gross hematuria had a specificity of almost 100%, when related to a positive filtration on any day, and was closely related to egg counts of greater than or equal to 50 eggs/10 ml urine. The finding of a strongly positive reaction for hematuria on a given single day was closely associated with the subject having a high egg count (greater than or equal to 50 eggs/10 ml urine) on at least one of the 6 days of the study. At the primary health care level, single highly positive semiquantitative values for hematuria were a more useful diagnostic indicator than a single egg count to select patients with heavy infections for selective population chemotherapy.

Metrifonate in the control of urinary schistosomiasis in Zanzibar.

Selective population chemotherapy using three doses of metrifonate (7.5 mg/kg body weight each time) at two-week intervals was assessed in an entire community in Kinyasini district in Zanzibar, United Republic of Tanzania. The objectives of the study were to (1) reduce the prevalence of heavy infections (defined as greater than or equal to 50 S. haematobium eggs per 10 ml of urine) by 75% in two years, and (2) reduce the overall prevalence of infection by 50% in two years. A total of 4113 people were examined at least once during the two-year period. In the initial survey the highest proportion of infected individuals was in the 10-14-year age group, and in all subsequent surveys in the 5-9-year age group. The age group with the highest proportion of heavily infected individuals was 5-9 years for all surveys. The overall reduction of prevalence of infection from survey 1 to survey 4 was 52.9% and the prevalence of heavy infection was reduced by 62.2%. The conversion rates (negative to positive in two consecutive surveys) were highest in the longest interval of 12 months and the rates of reversion (positive to negative in two consecutive surveys, without a history of treatment) were highest in the shortest interval of 4 months. Some statistically significant relationships were observed between the number of doses and the egg reduction rates. However, for the egg-negative rates, no statistically significant relationship was observed. In the 4-month interval a 67.6% egg-negative rate was observed among those who took at least one dose; with the 12-month interval a 48.3% egg-negative rate was observed. Thus, selective population chemotherapy with metrifonate was shown to reduce the prevalence and intensity of infection due to S. haematobium over a 24-month period.

Measurement of schistosomiasis-related morbidity at community level in areas of different endemicity.

Among the indicators of schistosomiasis morbidity currently used in control programmes, ultrasound has been found to be a safe, non-invasive and efficient technique for detecting schistosomiasis-related lesions and for assessing the effect of treatment on their resolution. Three case-studies from East Africa, in areas of different endemicity for Schistosoma haematobium, using ultrasound are described and their results related to indirect measurements of the disease (e.g., haematuria, egg counts). This review reveals that cross-sectional ultrasound surveys can be used to quickly assess subsamples of populations in areas of different endemicity, in order to make decisions about sampling strategies in control programmes. The association between the intensity of infection and urinary tract abnormalities is reviewed and evaluated. One case study provides information on the resolution of S. haematobium-related uropathy after treatment; this information is crucial in order to maintain low levels of morbidity in a community. The role of ultrasound is further discussed, particularly as a tool to complement and validate indirect morbidity control measurements. The validation of such indirect measurements for use as a basis for public health decisions is important because they can be carried out by existing health care services in many areas.

Control of morbidity due to Schistosoma haematobium on Pemba island; selective population chemotherapy of schoolchildren with haematuria to identify high-risk localities.

In Pemba, Tanzania, 2 sequential surveys were made of the prevalence of haematuria in children (aged 5-19 years) in 52 schools, using direct observation of gross haematuria (bloody urine) and chemical reagent strips as indicators of Schistosoma haematobium infection. 24,462 children were examined in the first survey and 25,575 in the second, 6 months later. The prevalence of gross haematuria was initially 15.8% (3876 cases); 6 months later, after a single dose of praziquantel (40 mg/kg), it was only 2.4% (613 cases), a reduction of 84.9%. The total number of cases of haematuria (gross or otherwise) dropped similarly, from 13,920 (54%) to 6638 (26%), a 52.2% reduction. In towns the degree of reduction was positively correlated with the standard of water supply and sanitation available, and the initial prevalence of gross and total haematuria in schools was positively correlated with the prevalence 6 months later. The cost per person reduced from US$ 0.83 in the first survey to US$ 0.48 in the second (excluding field staff wages paid in local currency), the reduction being due to the reduced number of positive persons. This study has demonstrated the feasibility of using indirect techniques on a large scale for the diagnosis of S. haematobium infection to identify schoolchildren requiring treatment, and to monitor its impact on clinical morbidity in a highly endemic area.

Control of morbidity due to Schistosoma haematobium on Pemba Island: programme organization and management.

A programme to control urinary schistosomiasis was initiated on Pemba island in January 1986 with the objectives of eliminating morbidity due to S. haematobium by utilizing a primary health care approach of strengthening the existing health care delivery system and creating a sound basis for future control of other parasitic and communicable diseases. The plan of action included training of rural health assistants to undertaken an intervention phase targeted to schools for selective population chemotherapy surveys at six-month intervals during the first two years, using indirect diagnostic techniques (observation of gross haematuria and detection of microscopic haematuria by chemical reagent strips) to identify individuals for treatment with praziquantel at a dose of 40 mg/kg body weight. The evaluation of the indirect techniques indicated that both sensitivity and specificity of the chemical reagent strips to detect infection were greater than 90%. After three selective population chemotherapy surveys, the prevalence of gross haematuria was reduced by 94.2% (15.8% to 0.9%) and both gross and microscopic haematuria were reduced by 76.4% (54.1% to 12.8%) among school children. Community involvement and health education were stressed in this programme. The use of dispensary laboratories to maintain control of urinary schistosomiasis is now being evaluated.