Fine-scale-mapping of Schistosoma haematobium infections at the school and community levels and intermediate host snail abundance in the north of Pemba Island: baseline cross-sectional survey findings before the onset of a 3-year intervention study

Abstract

Background Schistosomiasis elimination has gained renewed priority in the WHO guidance documents published in 2020 and 2022. The SchistoBreak project, implemented in Pemba, Tanzania between 2020 and 2024, aims to assess new tools and strategies for shifting from elimination as a public health problem towards interruption of transmission. Here we report our baseline findings and discuss implications for future interventions. Methods In 2020, human water contact sites (HWCSs) in the study area were geolocated and snail surveys were conducted. A parasitological and questionnaire cross-sectional baseline survey was implemented in 20 communities and their 16 primary schools between November 2020 and February 2021. Urine samples were collected at the school and household levels from individuals aged ≥ 4 years. Schistosoma haematobium infection was detected by urine filtration microscopy. Snail, parasitological and questionnaire-derived data were analyzed descriptively, spatially and with generalized estimated equation models. Results The intermediate host snail Bulinus globosus was detected in 19.8% (33/167) of HWCSs. The overall S. haematobium prevalence was 1.2% (26/2196) in school-aged children and 0.8% (31/3893) in community members, with 0.2% (4/2196) and 0.1% (3/3893) heavy-intensity infections, respectively. Children who studied < 1 km away from HWCSs with B. globosus had significantly higher odds for a S. haematobium infection than those attending a school located > 2 km away (odds ratio [OR]: 5.0; 95% confidence interval [CI]: 2.3–11.1). Individuals living in a house located < 1 km away from HWCSs with B. globosus had higher odds than those residing in > 2 km distance (OR: 18.0; 95% CI: 2.9–111.0). Self-reported praziquantel treatment coverage was 83.2% (2015/2423) in schoolchildren in the mass drug administration (MDA) conducted in August 2020. Coverage among adult community members was 59.9% (574/958), but only 34.8% (333/958) took praziquantel correctly. Conclusions While the S. haematobium prevalence is very low in Pemba, there are many HWCSs with B. globosus situated close to schools or houses that pose a considerable risk of recrudescence. To maintain and accelerate the progress towards interruption of transmission, targeted and cost-effective interventions that are accepted by the community are needed; for example, snail control plus focal MDA, or test-and-treat in schools and households near infested waterbodies. Graphical Abstract

Capacities and needs of health care facilities for schistosomiasis diagnosis and management in elimination settings

“…This health facility-based mixed-method study confirmed that health facilities can and should play a role in the prevention, diagnosis, management, control, and elimination of schistosomiasis. Indeed, we found that the S. haematobium prevalence (1.1%) identified through screening over an 8-day period of all patients attending purposefully selected health facilities was similar to the prevalence (0.8%) reported from recent large-scale community cross-sectional surveys in the same area in Pemba [ 27 ]. Hence, determining the S. haematobium prevalence via longitudinal passive surveillance or during specific periods or days when people are encouraged to attend health facilities for screening might provide an accurate picture of the endemic situation in a given area.…”

“…In the northern part of Pemba, the “SchistoBreak” project has been implemented since 2020, which aims to assess the impact of targeted interventions for schistosomiasis elimination [ 26 ]. As part of the SchistoBreak project, a cross-sectional survey conducted in 2021 revealed a very low prevalence of S. haematobium among school-aged children (1.2%) and community members (0.8%) [ 27 ]. Across the project area, health facilities are involved in the passive surveillance of schistosomiasis [ 26 ].…”

Test-treat-track-test-treat (5T) approach for Schistosoma haematobium elimination on Pemba Island, Tanzania

“…The SchistoBreak study area consists of 20 shehias, which are referred to in this publication as “implementation units” (IUs). The 20 IUs are located in the two northern districts of Pemba, Wete and Micheweni, which are characterized by their mostly rural environment and the presence of numerous water bodies [ 18 ]. Recent data from a national census conducted in 2022 indicate a total population of 543,441 for Pemba, with 272,091 people living in the districts Wete and Micheweni [ 20 ].…”

“…Additionally, snail control and behavior change communication, are applied in large-scale operational research projects, such as the Zanzibar Elimination of Schistosomiasis project (2012–2017) and the SchistoBreak study (2020–2024) [ 16 , 17 ]. Since 2017, the islands have reached ‘elimination as a public health problem’ and aim to proceed towards ‘interruption of Schistosoma transmission’ [ 11 , 13 , 18 ]. In 2020, the overall S. haematobium prevalence in Zanzibar was 3.4% in schoolchildren and 0.4% in adults [ 15 ].…”

Metagenomic Analysis Reveals Variations in Gut Microbiomes of the Schistosoma mansoni-Transmitting Snails Biomphalaria straminea and Biomphalaria glabrata

“…Endemic in 77 countries in tropical and subtropical regions, schistosomiasis poses a threat to approximately one-eighth of the global population. The disease is caused by different species of Schistosoma, including Schistosoma mansoni [3][4][5], S. japonicum [6][7][8][9], S. haematobium [10,11], S. intercalatum [12] and S. Mekongi [13][14][15], of which S. mansoni is one of the most widespread species [2,3]. Biomphalaria snails such as Biomphalaria straminea and B. glabrata are important intermediate hosts of S. mansoni.…”