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Insights From Quantitative and Mathematical Modelling on the Proposed WHO 2030 Goals for Chagas Disease

Insights From Quantitative and Mathematical Modelling on the Proposed WHO 2030 Goals for Chagas Disease

Collaborating Group on Chagas Disease Modelling. Gates Open Res.

Abstract

Chagas disease (CD) persists as one of the neglected tropical diseases (NTDs) with a particularly large impact in the Americas. The World Health Organization (WHO) recently proposed goals for CD elimination as a public health problem to be reached by 2030 by means of achieving intradomiciliary transmission interruption (IDTI), blood transfusion and transplant transmission interruption, diagnostic and treatment scaling-up and prevention and control of congenital transmission. The NTD Modelling Consortium has developed mathematical models to study Trypanosoma cruzi transmission dynamics and the potential impact of control measures. Modelling insights have shown that IDTI is feasible in areas with sustained vector control programmes and no presence of native triatomine vector populations. However, IDTI in areas with native vectors it is not feasible in a sustainable manner. Combining vector control with trypanocidal treatment can reduce the timeframes necessary to reach operational thresholds for IDTI (<2% seroprevalence in children aged <5 years), but the most informative age groups for serological monitoring are yet to be identified. Measuring progress towards the 2030 goals will require availability of vector surveillance and seroprevalence data at a fine scale, and a more active surveillance system, as well as a better understanding of the risks of vector re-colonization and disease resurgence after vector control cessation. Also, achieving scaling-up in terms of access to treatment to the expected levels (75%) will require a substantial increase in screening asymptomatic populations, which is anticipated to become very costly as CD prevalence decreases. Further modelling work includes refining and extending mathematical models (including transmission dynamics and statistical frameworks) to predict transmission at a sub-national scale, and developing quantitative tools to inform IDTI certification, post-certification and re-certification protocols. Potential perverse incentives associated with operational thresholds are discussed. These modelling insights aim to inform discussions on the goals and treatment guidelines for CD.

Keywords: Chagas disease; Elimination as a public health problem; NTD Modelling Consortium; WHO guidelines; intradomiciliary transmission interruption; trypanocidal treatment.

Conflict of interest statement

No competing interests were disclosed.

Figures

Figure 1.
Figure 1.. Force-of-Infection (FOI) models fitted to seroprevalence data.
Upper panels represent the (modelled) historical FOI. Lower panels present the data (solid squares) and the modelled seroprevalence (orange shaded area) in: ( A) a non-intervened area with a long-established endemic situation and ( B) a successfully intervened area. This figure has been reproduced from under a Creative Common Attribution 4.0 International Licence (CC BY 4.0).
Figure 2.
Figure 2.. Combined impact of vector control and effective parasite clearance.
Annual vector control defines the proportion by which vector density is annually reduced (0–100%); parasite clearance is measured as proportion of parasitological cure (PPC); annual PPC defines the proportion of humans effectively treated annually with trypanocidal treatment, i.e., the percentage of the infected human population achieving parasitological cure (0–40%). The impact of the combined strategies is measured on the number of years necessary to reduce seroprevalence in children aged <5 years to <2% (the operational serological criterion for intradomiciliary transmission interruption), as represented by the colour scale. The panels represent: ( A) low; ( B) moderate; ( C) high; and ( D) very high endemicity levels. This figure has been reproduced from under a Creative Common Attribution 4.0 International Licence (CC BY 4.0).
Figure 3.
Figure 3.. Probability of achieving effective parasite clearance.
(A) 10% proportion of parasitological cure (PPC); and (B) 20% of PPC in a Trypanosoma cruzi–infected human population based on the combined probability of being diagnosed and treated (with trypanocidal medication) for Chagas disease. The horizontal axis represents the combined contribution of diagnosis as a product of the proportion of infected people who are tested (pT) and the proportion of those tested with a positive test result, that is, the sensitivity of the test (pP). The vertical axis represents the combined contribution of treatment, as the product of the proportion of those testing positives who are treated with currently available trypanocidal drugs (pD) and respond to treatment by clearing parasites according to efficacy (pE). Coloured lines represent the proportion (p) of infected people who would have to be reached by a test-and-treat programme (90% [blue], 50% [red], 33% [green], and 20% [orange]) to achieve the desired level of effective PPC. This figure has been reproduced from under a Creative Common Attribution 4.0 International Licence (CC BY 4.0).

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