A modelling analysis of a new multi-stage pathway for classifying achievement of public health milestones for leprosy.

Several countries have come close to eliminating leprosy, but leprosy cases continue to be detected at low levels. Due to the long, highly variable delay from infection to detection, the relationship between observed cases and transmission is uncertain. The World Health Organization's new technical guidance provides a path for countries to reach elimination. We use a simple probabilistic model to simulate the stochastic dynamics of detected cases as transmission declines, and evaluate progress through the new public health milestones. In simulations where transmission is halted, 5 years of zero incidence in autochthonous children, combined with 3 years of zero incidence in all ages is a flawed indicator that transmission has halted (54% correctly classified). A further 10 years of only occasional sporadic cases is associated with a high probability of having interrupted transmission (99%). If, however, transmission continues at extremely low levels, it is possible that cases could be misidentified as historic cases from the tail of the incubation period distribution, although misleadingly achieving all three milestones is unlikely (less than 1% probability across a 15-year period of ongoing low-level transmission). These results demonstrate the feasibility and challenges of a phased progression of milestones towards interruption of transmission, allowing assessment of programme status. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.

Neglected tropical diseases.

INTRODUCTION: The neglected tropical diseases (NTDs) are infectious diseases that principally impact the world's poorest people. They have been neglected for decades, initially as part of a general disregard for the developing world, and more recently due to the intensity of focus on HIV/AIDS, tuberculosis and malaria. SOURCES OF DATA: Primary research and review articles were selected for inclusion using searches of PubMed and our existing collections. RESULTS: There have been recent notable successes in NTD control. Dracunculiasis is approaching eradication. Leprosy and onchocerciasis are in decline. There are ambitious plans to eliminate trachoma and lymphatic filariasis. Investment in NTD control has high rates of economic return. CONCLUSION: Although there are proven strategies to control several NTDs, these diseases continue to cause a massive burden of morbidity. There is urgent need for more basic and operational research, drug and vaccine development, and greater prioritization by governments and international agencies.

Recent advances in tropical medicine.

There have been significant advances in both the classical and neglected tropical diseases, with Guinea worm looking set to be the next disease after smallpox to be eradicated. Aided by a combination of enhanced understanding of the biology of the pathogens, intensification of immunisation activities or mass drug administration, together with the development of synergies with control programmes for co-endemic tropical diseases, polio, lymphatic filariasis, trachoma and onchocerciasis all appear to be in global decline, with good prospects for eventual successful elimination. While the global incidence of new cases of leprosy continues to decrease, the focus of leprosy control efforts has shifted following more widespread recognition that cure of infection does not necessarily prevent disability. Expansion in funding for HIV/AIDS and malaria provides some grounds for optimism about the control of these diseases. However, ongoing education and access remain essential to increasing the uptake of HIV testing and decreasing transmission. Meanwhile, the rise of drug-resistant tuberculosis and malaria is concerning, and the emergence of the highly pathogenic avian influenza A and re-emergence of viruses such as chikungunya and West Nile virus, without significant recent progress in vaccine development, pose additional ongoing challenges to tropical medicine physicians worldwide.