Neglected tools for neglected diseases: mathematical models in economic evaluations Hugo C. Turner 1, 2 , Martin Walker 1, 2 , Michael D. French 2, 3 , Isobel M. Blake 2, 4 , Thomas S. Churcher 2 , and Marı´a-Gloria Basa ´n ˜ ez 1, 2 1 London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s Campus), Imperial College London, Norfolk Place, London W2 1PG, UK 2 Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s Campus), Imperial College London, Norfolk Place, London W2 1PG, UK 3 Schistosomiasis Control Initiative, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s Campus), Imperial College London, Norfolk Place, London W2 1PG, UK 4 MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, School of Public Health, Faculty of Medicine (St Mary’s Campus), Imperial College London, London W2 1PG, UK Despite many current interventions against neglected tropical diseases (NTDs) being highly cost-effective, new strategies are needed to reach the WHO’s control and elimination goals. Here we argue for the importance of incorporating economic evaluations of new strategies in decisions regarding resource allocation. Such evaluation should ideally be conducted using dynamic transmission models that capture inherent nonlinearities in transmis- sion and the indirect benefits (‘herd effects’) of interven- tions. A systematic review of mathematical models that have been used for economic analysis of interventions against the ten NTDs covered by the London Declaration reveals that only 16 out of 49 studies used dynamic transmission models, highlighting a fundamental – but addressable – gap in the evaluation of interventions against NTDs. Neglected tropical diseases: reaching the 2020 control and/or elimination goals NTDs (see Glossary) are a group of chronic, disabling, and disfiguring conditions that occur especially among the rural poor and disadvantaged urban populations [1]. These diseases cause a substantial health and economic burden on poor populations in Africa, Asia, and Latin America [1]. Latest estimations indicate that NTDs cause approxi- mately 534 000 deaths, and are responsible for 56.6 million disability-adjusted life years (DALYs) lost, each year [2–4], although these numbers are likely to be significantly underestimated [2]. In January 2012, the London Declaration for the control and/or elimination of ten of the highest burden NTDs by the year 2020 was announced (Table 1) [London Declaration on Neglected Tropical Diseases (2013) Ending the neglect and reaching 2020 goals (http://unitingtocombatntds.org/ downloads/press/ntd_event_london_declaration_on_ntds. pdf)] [5]. These goals were inspired by the WHO 2020 road map for accelerating work to overcome the global burden of NTDs [6]. The reports by the Disease Control Priorities Project (DCPP) include estimates of the cost-effectiveness of inter- ventions against diseases in the developing world (http:// www.dcp-3.org/). These reports illustrate that many of the current interventions against NTDs are highly cost-effective and, in several instances, are even more so than interven- tions against the so-called ‘big three’: malaria, tuberculosis, and HIV [7,8]. Despite this, it is also recognised that novel Opinion Glossary Cost-effectiveness analysis: a method for assessing the relative gains in health generated by a health intervention compared to the costs. Density-dependent process: a demographic or transmission process whose rate is regulated by the density of parasites in the host or population. Disability-adjusted life years (DALYs): a time-based measure of disease burden accounting for years of life lost due to premature mortality and healthy years of life lost due to disability [48]. Dynamic transmission model: a model that links the rate at which individual hosts acquire new infections with the abundance of infection among all hosts in a population. Elimination of infection: reduction to zero of the incidence of infection caused by a specific agent in a defined geographic area as a result of deliberate efforts; continued measures to prevent reestablishment of transmission are required. Herd effect: the indirect benefit afforded to individuals not directly targeted by an intervention that arises from the reduction in transmission that ensues from an effective intervention. Macroparasites: parasites that are large enough to be seen with the naked eye (e.g., parasitic worms) and which do not multiply directly within the definitive host. Neglected tropical diseases (NTDs): a group of chronic, disabling, and disfiguring conditions that occur especially among the rural poor and disadvantaged urban populations. Static transmission model: a model that assumes the rate at which individual hosts acquire new infections is ‘independent’ of the abundance of infection among all hosts in a population. Transmission breakpoint: the (nonzero) parasite density below which a parasite population cannot maintain itself and is driven into terminal decline and eventual elimination. 1471-4922/ ß 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.pt.2014.10.001 Corresponding author: Turner, H.C. (hugo.turner06@imperial.ac.uk). Keywords: neglected tropical diseases (NTDs); mathematical modelling; analysis theoretical models; epidemiology; control programmes; cost-effectiveness; cost benefit; economic evaluation studies. TREPAR-1323; No. of Pages 9 Trends in Parasitology xx (2014) 1–9 1