Fri Sep 20 14:00:00 UTC 2024: ## New Research Shows Schistosomiasis Control May Be More Challenging Than Previously Thought

**Nijmegen, Netherlands** – A groundbreaking study published in PLOS Neglected Tropical Diseases challenges the current understanding of schistosomiasis control, suggesting that reaching the World Health Organization’s (WHO) 2030 targets might be more difficult than previously thought.

The study, led by researchers at Radboud University Medical Center and Erasmus MC, utilized a novel modeling framework called SchiSTOP to investigate the interplay of different regulating mechanisms in the transmission of Schistosoma mansoni, the parasite responsible for intestinal schistosomiasis.

Schistosomiasis affects an estimated 250 million people worldwide, primarily in tropical and subtropical regions. Current control efforts rely heavily on mass drug administration (MDA) with praziquantel, which kills adult worms within human hosts. However, the prevalence of infection often bounces back to pre-control levels shortly after stopping MDA, and low-level transmission can persist, making it difficult to interrupt transmission entirely.

The study found that the common assumption of worm-level regulation through density-dependent egg production, often used in schistosomiasis models, is not sufficient to explain observed epidemiological patterns. Instead, SchiSTOP simulations revealed that incorporating regulation at the snail level (density-dependent snail dynamics) and human level (anti-reinfection immunity) is crucial to accurately represent the complex transmission cycle.

The study further demonstrated that the choice of age-specific exposure to infection significantly impacts model outcomes. The researchers tested two different age-exposure functions: one based on existing modeling assumptions and another based on published water contact data. The water contacts-based function was found to better reflect observed age-intensity profiles and resulted in more realistic predictions for the rebound of prevalence after treatment.

The study’s key findings:

* **Snail-level regulation is essential for explaining stable low transmission.**
* **The combination of snail- and human-level regulation is necessary to reproduce rapid rebound after treatment.**
* **Assumptions on regulating mechanisms heavily influence predictions of the feasibility to reach control targets.**
* **Treating only school-aged children (SAC) with MDA is unlikely to achieve the WHO’s control targets.**
* **Expanding MDA to include the entire community (>2 years old) significantly increases the probability of achieving the control targets, especially in low endemic settings.**

These findings highlight the importance of considering various regulating mechanisms, beyond the worm level, in schistosomiasis models used to guide policy decisions. The study suggests that relying solely on MDA for schistosomiasis control might be insufficient and that integrating other control measures, such as snail control and behavior change interventions, may be necessary to achieve sustainable elimination of the disease.

This research provides valuable insights into the complex dynamics of schistosomiasis transmission and highlights the need for continued investigation to refine our understanding of the disease and develop more effective control strategies.

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