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. 2019 Sep 26:3:1546.
doi: 10.12688/gatesopenres.13068.2. eCollection 2019.

The World Health Organization 2030 goals for Taenia solium: Insights and perspectives from transmission dynamics modelling: CystiTeam Group for Epidemiology and Modelling of Taenia solium Taeniasis/Cysticercosis

CystiTeam Group for Epidemiology and Modelling of Taenia solium Taeniasis/Cysticercosis

The World Health Organization 2030 goals for Taenia solium: Insights and perspectives from transmission dynamics modelling: CystiTeam Group for Epidemiology and Modelling of Taenia solium Taeniasis/Cysticercosis

CystiTeam Group for Epidemiology and Modelling of Taenia solium Taeniasis/Cysticercosis. Gates Open Res. .

Abstract

Taenia solium (TS), responsible for porcine cysticercosis, human taeniasis and (neuro)cysticercosis, was included in the World Health Organization neglected tropical disease (NTD) roadmap published in 2012. Targets set in this roadmap have not been met, but T. solium has been included in the consultation process for the new 2030 goals proposed for priority NTDs. Taenia solium transmission dynamics models can contribute to this process. A recent review has compared existing T. solium transmission models, identifying their similarities and differences in structure, parameterization and modelled intervention approaches. While a formal model comparison to investigate the impact of interventions is yet to be conducted, the models agree on the importance of coverage for intervention effectiveness and on the fact that human- and pig-focused interventions can be optimally combined. One of these models, cystiSim, an individual-based, stochastic model has been used to assess field-applicable interventions, some currently under evaluation in on-going trials in Zambia. The EPICYST, population-based, deterministic model has highlighted, based on simulating a generic sub-Saharan Africa setting, the higher efficacy (measured as the percentage of human cysticercosis cases prevented) of biomedical interventions (human and pig treatment and pig vaccination) compared to improved husbandry, sanitation, and meat inspection. Important questions remain regarding which strategies and combinations thereof provide sustainable solutions for severely resource-constrained endemic settings. Defining realistic timeframes to achieve feasible targets, and establishing suitable measures of effectiveness for these targets that can be quantified with current monitoring and evaluation tools, are current major barriers to identifying validated strategies. Taenia solium transmission models can support setting achievable 2030 goals; however, the refinement of these models is first required. Incorporating socio-economic elements, improved understanding of underlying biological processes, and consideration of spatial dynamics are key knowledge gaps that need addressing to support model development.

Keywords: (neuro)cysticercosis; EPICYST; One Health; Taenia solium; cystiSim; mass drug administration; pig vaccination; taeniasis.

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Conflict of interest statement

No competing interests were disclosed.

Figures

Figure 1.
Figure 1.. Impact of single interventions on the number of human cysticercosis cases.
Box and whiskers represent the range of impact estimates from 1000 sensitivity draws of intervention efficacy parameters, the midline represents the median impact (on the proportion of Human Cysticercosis cases prevented), the hinges the 25 th and 75 th percentiles, and the whiskers the range. Points show individual run outputs. Due to the large amount of uncertainty in parameters estimates, the impact of parameter estimates was explored separately (see Figure 4 in Winskill et al. ). This figure has been reproduced under the Creative Commons Attribution 4.0 International License (CC BY 4.0) from Winskill et al. .
Figure 2.
Figure 2.. Simulation of various control scenarios for Taenia solium using cystiSim.
The effectiveness of repeated mass drug administration (MDA) in humans (H) for taeniasis is compared with three-monthly interventions in pigs (P) involving vaccination and treatment, or a combination of pig interventions with strategic MDA in the human population after 1000 simulations (S). The impacts are shown on porcine cysticercosis (PC), immunity to T. solium infection in the pig population (PR), and human taeniasis (HT), with prevalence shown here as a proportion. The colored areas delineate the 95% uncertainty intervals for prevalence (proportion). Pr(elim) indicates the predicted probability of elimination of transmission (EOT) in the given scenario. Four scenarios are simulated which involve: MDA only in humans ( A– D): annual treatments for 5 or 10 consecutive years ( A and B, respectively), and biannual MDA for 5 or 10 consecutive years ( C and D, respectively). Two scenarios involve pig-focussed interventions. Each included three-monthly vaccination and oxfendazole treatment of the pig population. The first involves: vaccination and treatment in pigs ( E) for 3 years. The second ( F) also involves pig interventions, but includes three human MDA rounds, at 6, 12, and 18 months after the initiation of the interventions in pigs, over a total period of 2 years. This figure has been reproduced with permission from Braae et al. .
Figure 3.
Figure 3.. cystiSim output for different intervention scenarios aiming for control and elimination of Taenia solium in Zambia.
Interventions aiming for control ( A) and elimination ( B): Pr (elim): probability of elimination of transmission (EOT) of porcine cysticercosis (PCC) and human taeniasis (HT), MDA: human mass drug administration (praziquantel), OXF: porcine mass drug administration (oxfendazole), VAC: porcine vaccination (TSOL18), XqY: total number of X iterations of the intervention given at intervals of Y months. Interventions are introduced after 200 months. This figure has been reproduced with permission from Gabriël et al. . Y-axis shows prevalence as a proportion.
Figure 4.
Figure 4.. Lifecycle of Taenia solium.
The lifecycle indicates, at each stage, key research gaps and data needs important for epidemiological modelling. This figure has been reproduced under the Creative Commons Attribution 4.0 International Licence (CC BY 4.0) from Dixon et al. . NCC: neurocysticercosis.
See this image and copyright information in PMC

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