Impact of three rounds of mass preventive chemotherapy on prevalence and intensities of Schistosoma mansoni infection among an adult population on Ukerewe Island, north-western Tanzania

Crecencia Edward Chiombola ¹ Erick Simon Mwangoka ² Tumaini Baumba ² Charles Guya Mkombe ² Saskia Kreibich ³ Christa Kasang ³ Antje Fuss ⁴ Andreas Mueller ⁴ Paul Alikaindo Sabuni ¹ Humphrey Deogratias Mazigo ^1*

• ¹ Catholic University of Health and Allied Sciences (CUHAS), Bugando, Tanzania
• ² District Medical Department, Ukerewe District Council, P.O. Box 41, Nansio, Ukerewe, Mwanza, Tanzania, Mwanza, Tanzania
• ³ DAHW - German Leprosy and Tuberculosis Relief Association, Raiffeisenstrasse 3, 97080, Würzburg, Germany
• ⁴ Medical Mission Institute, Salvatorstrasse 7, 97067, Würzburg, Germany and Medical Mission Hospital, Salvatorstrasse 7, 97074, Würzburg, Germany, Wuezburg, Germany

The WHO has called for the elimination of schistosomiasis as a public health problem by 2030 through expanding praziquantel delivery to all community members. The current project is responding to this call . To date three rounds of mass preventive chemotherapy have been implemented and here, we report the impact effect of these treatment rounds on prevalence and intensity of S.mansoni infection. Secondarily, we report on treatment coverages in all the treatment rounds.Methods: A community-based cross-sectional study was conducted in 20 villages and included randomly selected adults aged ≥15 years. A single stool sample was obtained from each consented participant and examined for S. mansoni infection using the Kato Katz technique. A questionnaire was used to collect demographic information of participants. The World Health Organization Community evaluation surveys (CES) methods were adapted for assessing treatment coverages. Two weeks after each treatment round (Between June, 2021, January 2023, and June, 2023), CES were conducted among adults from randomly selected households.Results: For parasitological surveys, a total of 2,041 participants (47.8% male and 52.2% female) were involved. After three rounds of treatment, the overall adjusted prevalence of S. mansoni infection was 9.5% (95%CI:8.3-10.8) and the geometrical mean egg intensity of infection was 79.9eggs per gram (epg) of feaces (95%CI:71.2-89.8). The prevalence declined by 68.8% (from 30.4% to 9.5%, P<0.0001) and intensity of infection declined by 24.1% (from 105.3epg at baseline to 79.9epg, P<0.0001). After three rounds of mass PC, the proportion of heavily infected adult individuals significantly declined by 81% (from 13.7% at baseline to 2.6%). For coverage survey, a total of 12,531 adult individuals were interviewed post-three rounds of treatment. Coverages of 80.8%, 78.5% and 81.9% were recorded for treatment round one, two and three.Overall the three rounds of mass preventive chemotherapy led to declines in prevalence and intensity of S.mansoni infection in the targeted population. In all the targeted villages, the treatment coverage of PZQ was above the recommended threshold of ≥ 75%, but improvement is needed to achieve higher coverage in the coming treatment rounds, which in turn will have high effects on disease prevalence.