Authors

Discussion

Background: The WHO aims to eliminate schistosomiasis as a public health problem worldwide by 2030. Pemba Island, Tanzania, achieved this goal in 2017 and is now targeting interruption of transmission. In most parts of Pemba, the Schistosoma haematobium prevalence is below 3%. Mass drug administration of praziquantel no longer seems justified. Instead, we implemented a surveillance-response approach with targeted interventions in low-prevalence areas. Here, we assessed the sensitivity of the surveillance-response approach to identify and treat all infected individuals in the area and its impact for elimination.

Methods: In the 4-year SchistoBreak project, annual cross-sectional surveys in schools and communities were conducted to identify low-prevalence and hotspot areas and implement interventions accordingly. In low-prevalence areas, a surveillance-response approach was implemented, where, in a first step, children in primary and Islamic schools were screened for S. haematobium infection. Subsequently, positive-tested children were treated with praziquantel and accompanied to their homes and the water bodies they used. Testing for S. haematobium was offered to household members and individuals at water bodies, and treatment to those who tested positive. Snail surveys were conducted at the water bodies to search for Bulinus, and if found, niclosamide was applied. To assess the sensitivity of the surveillance-response approach, the number of positive-tested individuals in the interventions was divided by the estimated number of infected individuals in the whole study area, as determined by cross-sectional surveys and population census data.

Results: In 2021, the baseline S. haematobium prevalence in 15 low-prevalence areas was 0.5% (7/1552) in schoolchildren. After one year of surveillance-response interventions, the prevalence decreased to 0.4% (6/1653). In 2022, the prevalence of schoolchildren in 16 low-prevalence areas was 0.6% (12/2123) and changed to 0.7% (15/2240) in 2023 after the interventions. In 2023, the prevalence in 17 low-prevalence areas was 0.4% (8/2287) and changed to 0.8% (9/1103) in 2024. In 2021, the baseline S. haematobium prevalence in 15 low-prevalence areas was 0.5% (14/2969) in community members. After one year of surveillance-response interventions, the prevalence changed to 0.7% (19/2928). In 2022, the prevalence of S. haematobium in 16 low-prevalence areas was 0.6% (18/3175) and dropped to 0.3% (10/2979) in 2023 after the interventions. In 2023, the prevalence in 17 low-prevalence areas was 0.4% (12/3255) and changed to 0.7% (22/3014) in 2024. The sensitivity of the surveillance-response approach to identify and treat all individuals estimated to be infected with S. haematobium in the population of the study area was 96.3% for schoolchildren, 3.7% for adults, and 56.0% overall. In 26.2% of the water bodies that were surveyed based on children’s use, Bulinus were found and niclosamide was applied.

Conclusion: The surveillance-response interventions showed a very high sensitivity in identifying and infected children but not adults. Many water bodies were discovered and treated with niclosamide that serve as habitats for Bulinus. However, while surveillance-response interventions maintained the low S. haematobium prevalence in the study area, they did not result in transmission interruption within three years.