# Identifying hotspots of S. haematobium infection following praziquantel treatment during multiple annual mass drug administration campaigns in Zimbabwe

## TL;DR

The study identifies persistent hotspots of S. haematobium infection in Zimbabwe despite praziquantel treatment, suggesting the need for integrated control strategies.

## Contribution

The study is the first to characterize persistent hotspots of S. haematobium infection in Zimbabwe and evaluates factors influencing their persistence.

## Key findings

- Four persistent hotspots of infection prevalence were identified with higher baseline prevalence and intensity.
- Six hotspots of decreasing PZQ efficacy were found, with increased distance to freshwater sources associated with hotspot occurrence.
- Integrated control measures like WASH and snail control are recommended to improve schistosomiasis control in hotspot areas.

## Abstract

Urogenital schistosomiasis is contracted from the Schistosoma haematobium parasite and is treated with the drug praziquantel (PZQ). Despite MDA interventions, persistent hotspots (PHS) of S. haematobium infection have been identified in multiple schistosome endemic African countries but have yet to be characterised in Zimbabwe. This study assessed long-term infection persistence and variability in praziquantel (PZQ) efficacy among school-aged children (6–15 years) in 29 districts of Zimbabwe, using data from MDAs conducted between 2012 and 2017. Metrics included infection prevalence, mean egg count, and treatment efficacy indicators. Two hotspot definitions were applied: (i) prevalence-based persistent hotspots (PPHS), identified by limited reduction or rebound in prevalence; and (ii) efficacy-based persistent hotspots (EPHS), defined by cure rates below 70%. Statistical comparisons between hotspot and non-hotspot (“responder”) districts used regression models, Fisher’s exact test and Mann-Whitney U tests. Analyses revealed four PPHS and six EPHS. PPHS districts exhibited significantly higher baseline prevalence and infection intensity compared with responders (P = 0.043), a pattern not observed for EPHS. Greater distance from freshwater sources was associated with EPHS occurrence (P = 0.016), although this appeared to be an indirect effect of initially high infection intensities. Lower treatment frequency correlated with increased hotspot occurrence, but the relationship was not statistically significant for either hotspot category. Other investigated factors including treatment coverage, timing of drug administration and ecological suitability for intermediate host snails showed no significant association with hotspot status. The elevated initial prevalence and infection intensity in PPHS suggest these indicators could be used for early hotspot identification, enabling targeted adjustments in intervention strategies. The findings underscore the limitations of relying solely on preventive chemotherapy in high-transmission settings. Integrating complementary measures such as water, sanitation and hygiene (WASH) interventions and snail control may improve outcomes, particularly in hotspot areas. In conclusion, the persistence of S. haematobium hotspots in Zimbabwe highlights the need for adaptive, integrated control approaches aligned with the WHO’s 2030 roadmap. Monitoring baseline epidemiological indicators could facilitate earlier detection of persistent transmission foci, guiding more effective and sustainable schistosomiasis control.

Urogenital schistosomiasis is a debilitating parasitic disease, commonly found in sub-Saharan Africa. Zimbabwe regularly administers praziquantel (PZQ), the primary treatment for this disease. Despite a heavy reliance on PZQ, persistent hotspots (PHS) of S. haematobium infection have been identified in other countries in Africa. Yet, no study has assessed the emergence of PHS in Zimbabwe or the factors causing them. We investigated PHS using measures of infection prevalence and PZQ efficacy using data collected from school-aged children in Zimbabwe during MDAs administered between 2012 and 2017. We identified four PHS of infection prevalence, all of which were found to have significantly higher baseline prevalence and infection intensity than non-hotspot areas. We also detected six PHS of decreasing PZQ efficacy in which increased distance to a freshwater source was significantly associated with hotspot occurrence. Additionally, although the decreased frequency of PZQ treatment was associated with more hotspot occurrences, it was not significant. Additional risk factors of persistent infections including coverage/season of treatment and favourable host snail habitats were evaluated for their contribution to these hotspots using multiple statistical tests, but no further significant associations were detected. These findings contribute toward improving schistosome control in Zimbabwe and further informing on PHS of this disease. We highlight the importance of integrated control interventions, such as water, sanitation and hygiene (WASH) and snail control, to complement preventive chemotherapy, particularly in hotspot settings. Overall, our findings call for an integrated control approach to meet the targets set by the new WHO roadmap.