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A special issue of the Philosophical Transactions of the Royal Society B on challenges and opportunities in the fight against neglected tropical diseases has been released today. This special issue, compiled and edited by Kathryn Forbes, Maria-Gloria Basáñez, Déirdre Hollingsworth and Roy M. Anderson, celebrates progress made since the 2012 London Declaration on NTDs and discusses challenges currently faced to achieve these goals.

One of the contributions to the issue is 'A modelling analysis of a new multistage pathway for classifying achievement of public health milestones for leprosy,' which focuses on leprosy elimination. This pivotal article increases understanding of leprosy's intricacies.

Despite progress in eliminating leprosy, low-level cases still persist due to complex transmission patterns and delays in detection. The World Health Organization has introduced new guidance to aid countries in their eradication efforts. A modelling analysis of the novel guidance, performed during the consultation period, shows that a 5-year absence of cases in local children and 3 years in all age groups indicates a potential transmission stoppage in 54% of simulations, but  a subsequent. 10 years of only sporadic cases increases the chance that transmission has stopped to 99%. However, if transmission remains very low, cases could be misidentified due to the incubation period, with unlikely misleading milestones.

The study highlights the utility of the three-phase approach for classifying the end of leprosy transmission, guided by the WHO's monitoring tool. Long incubation periods and delays to cases being detected are the unique characteristics of leprosy and require continuous case detection and treatment for over ten years post-transmission termination. Furthermore, an extended observation period is vital to confirm non-endemic status. While acknowledging limitations of any such modelling due to incomplete knowledge about leprosy's incubation period and variable detection delays  which have been exacerbated by the COVID-19 pandemic, the research highlights the significance of this analysis. It provides insights into strategies for combating the disease while navigating its complexities.

The research emphasizes the intricacies of eliminating leprosy transmission and stresses the importance of understanding these challenges to refine global strategies. The article offers valuable insights into the feasibility and difficulties of assessing leprosy program status using phased milestones. Researchers acknowledge the limitations tied to the current understanding of leprosy's incubation period and the influence of the pandemic on detection delays.

By shedding light on these complexities, the study contributes to shaping effective approaches in the ongoing fight against leprosy, paving the way for a more informed and strategic battle against this disease. The research group has shown here that, if implemented with a balanced and comprehensive understanding of what each one represents, the combined phases and milestones outlined in the WHO technical guidance are likely to effectively classify the elimination of leprosy transmission.

Dr Emma Davis, Warwick Zeeman Lecturer at Mathematics Institute, University of Warwick, and the lead author of this study said: ‘It is essential for any guidance provided to public health programmes to be carefully tested and validated. Our results will help leprosy programmes and public health officials interpret the process as they take steps towards achieving elimination, thereby informing future decisions.”’

Professor Déirdre Hollingsworth, Senior Group Leader at the University of Oxford’s Big Data Institute and senior author on the study, said: ‘This analysis highlights the importance of maintaining health systems and surveillance in areas where infections have been detected in the past, which are in low-income populations who can be challenging to reach.’

The full special thematic issue of the Philosophical Transactions of the Royal Society B is available at: