The context of this work in Pemba was (i) the initial reestablishment of School-Based Treatment (SBT) with praziquantel (PZQ) and albendazole (ALB) for control of urogenital schistosomiasis and soil-transmitted helminths (STH), respectively, and (ii) the subsequent implementation of mass drug administration (MDA) with or without additional snail control or behavioural modification which was aimed at evaluation of the possibility of elimination of schistosomiasis. The prime focus of the work described was to use regular parasitological monitoring to evaluate and compare control strategies with regard to the effects of intervention on transmission or morbidity. Chapters 1 and 2: General Introduction and Material and Methods respectively Chapter 3: Urogenital schistosomiasis. (i) Use of single annual SBT with PZQ: By assessing urine egg output in new-entry standard (Std)-1 children, neither the intensity nor baseline prevalence of 9.5% was lowered over a two year period of intervention. However, prevalences in St-3 children who had received SBT showed lower prevalences than Std-1 children presumably reflecting PZQ-mediated worm reductions. This supports the WHO recommended use of SBT treatment once/year for areas with prevalence <20% for morbidity control but demonstrates its lack of effect in transmission control. (ii) Use of MDA (twice/year) alone or combined with snail control or behavioural modification:. Testing of Std-3 and Std-4 children in each of 15 shehias allocated to the three different intervention arms revealed an overall reduction in the prevalence of schistosomiasis from 8.3% in 2012 to 5.4% in 2014 (impact:- behavioural control > snail control>MDA). There was a downward trend in the overall mean intensity across all interventions (from 2.71 1.83 1.71) but no consistent reduction in the proportion of heavy infections among the infected children. Recommendations: Integrated interventions are likely to be necessary for interrupting transmission of schistosomiasis and eventually leading to elimination. In poor resource areas, such as Zanzibar, it would be difficult to implement fully integrated control measures and so focusing on PC in areas with high transmission coupled with behavioural changes and strengthening of diagnostic capability of health facilities could be essential. ii Chapter 4: STH. Faecal examination of the Std-1 children, as above, for the eggs of Ascaris lumbricoides, Trichuris trichiura and hookworm, showed a high frequency of polyparasitism. Neither SBT nor intense MDA significantly reduced prevalence of any STH worm in the communities. The worm specific prevalences were slightly reduced overall, most consistently for Trichuris. However, there were no significant changes in intensity of infection, which remained light in the majority of infected children. Recommendations: No impact of either SBT or MDA on transmission to Std-1 children was observed. Integrated approaches e.g. WASH (water, sanitation and hygiene), education and PC are likely to be essential for reduction in transmission. Chapter 5: The efficiency of drug distribution and associated compliance were monitored during the MDA by individual questionnaire and reports from the community drug distributors (CDDs). Overall coverage rate was high (~80%) but variable between the districts (69.3-88.2%). Based on questionnaire, a significant proportion of individuals were non-compliant with the MDA especially regarding PZQ (10.2%) although this did not associate with knowledge about disease transmission, signs/symptoms or risk factors for schistosomiasis. Only mild adverse effects were reported. Recommendations: For any future MDA careful thought needs to be given to understanding the variation in compliance observed across the different areas of Pemba. There is a need of intensifying sensitization meetings in the communities with focus of discussion on potential side effects which may develop. Engage religious and other influential leaders during sensitization meetings. Chapter 6: Since the intensive enhanced MDA for schistosomiasis was aimed at evaluating the possibility of elimination of transmission, the role in transmission of the preschool (>3<5yr) children, who were not previously included in PC in Pemba, was assessed. A substantial proportion of these children was infected (7.04%), the prevalence steadily increasing with age. By questionnaire to mothers/care-givers, contact with stream/pond water through washing and visiting with the children were significant risk factors for pre-school infection. Recommendations: In view of the preschool prevalence demonstrated, the community MDA was extended to <3yr olds. The government should be ready to register and order paediatric formulation of PZQ once it becomes available. Diagnostic capability of the respective health facilities has to be strengthened in terms of training of laboratory personnel and purchase of essential laboratory equipment. iii Chapter 7: Implementation of snail control in Pemba prompted study of transmission of schistosomiasis by the snail intermediate host, Bulinus spp. Only ~1% of fieldcollected snails shed cercariae but 56% of tested snails were found infected by PCR. DNA sequencing confirmed the presence of B. nasutus and B. globosus, both of which transmitted schistosomes as judged by cercarial shedding and molecular techniques. Recommendations: Further studies are needed to confirm the potential role of the B. nasutus in the transmission of urogenital schistosomiasis in Pemba. For monitoring of schistosomiasis transmission, it would be essential to assess the presence of infection in snail host using molecular techniques especially when elimination is achieved or targeted. Chapter 8: Increasing intensity of PZQ administration raises concerns about possible selection of drug resistance in S. haematobium and prompted studies on the efficacy of PZQ and its effects on parasite genetic diversity in Pemba. It was found that PZQ efficacy was comparable to previous trials. Miracidial samples collected from Std-1 children in 2011 showed diverse, and some novel, haplotypes of the Cox-1 gene of S. haematobium. Clustering of the different haplotypes from different areas indicated the role of internal/external migration in the spread of infection. Recommendations: Praziquantel remains effective and should still be used for the treatment of schistosomiasis at the individual, community or school level in Pemba. More studies are needed to assess susceptibility to PZQ of different S. haematobium haplotypes and of the groups (G1 and G2) with which they associate. Chapter 9: General Discussion: Overall it was concluded that S. haematobium and STH infections remain a public health problem in Pemba and that, although PC using SBT helps control parasite burdens, integrated control measures were more effective and would be required to reduce transmission to approach elimination. Valuable experience in implementation and monitoring of such measures (MDA±snail control/behavioural modification) and application of modern genetic analysis tools was gained during the work and further studies on the snail hosts and population genetics of S. haematobium proposed.