Counting Down the 2020 Goals for 9 Neglected Tropical Diseases: What Have We Learned From Quantitative Analysis and Transmission Modeling?

Abstract

The control of neglected tropical diseases (NTDs) has received huge investment in recent years, leading to large reductions in morbidity. In 2012, the World Health Organization set ambitious targets for eliminating many of these diseases as a public health problem by 2020, an aspiration that was supported by donations of treatments, intervention materials, and funding committed by a broad partnership of stakeholders in the London Declaration on NTDs. Alongside these efforts, there has been an increasing role for quantitative analysis and modeling to support the achievement of these goals through evaluation of the likely impact of interventions, the factors that could undermine these achievements, and the role of new diagnostics and treatments in reducing transmission. In this special issue, we aim to summarize those insights in an accessible way. This article acts as an introduction to the special issue, outlining key concepts in NTDs and insights from modeling as we approach 2020.

NTD Diagnostics for Disease Elimination: A Review

“…This is the experience of the Guinea-worm and poliomyelitis campaigns [19], as well as the context behind Dowdle and Cochi's summation that "all eradication is ultimately local" [20] (p. 3). The central importance attached to diagnosis, as a means by which one might hope to understand and manage local settings, is now a key message coming out of the literature [21][22][23]. In this view, diagnostics and the data they yield promise to become a missing piece in the puzzle of disease elimination.…”

“…Several of the papers subdivided the group of NTDs being targeted for elimination into two categories: (a) diseases amenable to Mass Drug Administration (MDA), ("An MDA program requires repeated distribution of treatment to large numbers of individuals, without diagnosis" (Hollingsworth 2018: s240)) and (b) diseases requiring Intensive Disease Management (IDM) [21,22,24]. This distinction is pertinent, as it changes both the unit of intervention and the ascribed role of diagnosis.…”

“…New diagnostics are envisaged to play a critical role in monitoring progress towards elimination goals and for ongoing surveillance [21]. For these diseases, data is needed to determine when and where MDA should be delivered; then "the key questions are who to treat (e.g., which age group), how often to treat, and when treatments can be stopped" [22] (p. 241). For IDM diseases like Chagas disease and visceral leishmaniasis, the unit of intervention is the individual.…”

“…Instead, a diagnostic algorithm must be followed to confirm infection-which for HAT includes screening, parasitology, and disease staging [25]. There are a number of common uncertainties around IDM diseases which act to delay and complicate the pathway to diagnosis-for instance, long uncertain incubation periods and an unknown degree of transmission by asymptomatic carriers [22].…”

Assessment of control strategies against Clonorchis sinensis infection based on a multi-group dynamic transmission model

“…Mathematical models play important roles for understanding the transmission dynamics of parasitic diseases [18]. Furthermore, they test hypotheses about likely dynamics and epidemiology under proposed strategies, thus support control and elimination programmes [19]. Four papers have been published on mathematical models depicting the transmission dynamics of C. sinensis infection.…”