Taenia solium from a community perspective: Preliminary costing data in the Katete and Sinda districts in Eastern Zambia

Foodborne Parasites and Their Complex Life Cycles Challenging Food Safety in Different Food Chains

Zoonotic foodborne parasites often represent complex, multi host life cycles with parasite stages in the hosts, but also in the environment. This manuscript aims to provide an overview of important zoonotic foodborne parasites, with a focus on the different food chains in which parasite stages may occur. We have chosen some examples of meat-borne parasites occurring in livestock (Taenia spp., Trichinella spp. and Toxoplasma gondii), as well as Fasciola spp., an example of a zoonotic parasite of livestock, but transmitted to humans via contaminated vegetables or water, covering the 'farm to fork' food chain; and meat-borne parasites occurring in wildlife (Trichinella spp., Toxoplasma gondii), covering the 'forest to fork' food chain. Moreover, fish-borne parasites (Clonorchis spp., Opisthorchis spp. and Anisakidae) covering the 'pond/ocean/freshwater to fork' food chain are reviewed. The increased popularity of consumption of raw and ready-to-eat meat, fish and vegetables may pose a risk for consumers, since most post-harvest processing measures do not always guarantee the complete removal of parasite stages or their effective inactivation. We also highlight the impact of increasing contact between wildlife, livestock and humans on food safety. Risk based approaches, and diagnostics and control/prevention tackled from an integrated, multipathogen and multidisciplinary point of view should be considered as well.

A scoping review of burden of disease studies estimating disability-adjusted life years due to Taenia solium

Background

Taenia solium is the most significant global foodborne parasite and the leading cause of preventable human epilepsy in low and middle-income countries in the form of neurocysticercosis.

Objectives

This scoping review aimed to examine the methodology of peer-reviewed studies that estimate the burden of T. solium using disability-adjusted life years.

Eligibility criteria

Studies must have calculated disability-adjusted life years relating to T. solium.

Charting methods

The review process was managed by a single reviewer using Rayyan. Published data relating to disease models, data sources, disability-adjusted life years, sensitivity, uncertainty, missing data, and key limitations were collected.

Results

15 studies were included for review, with seven global and eight national or sub-national estimates. Studies primarily employed attributional disease models that relied on measuring the occurrence of epilepsy before applying an attributable fraction to estimate the occurrence of neurocysticercosis-associated epilepsy. This method relies heavily on the extrapolation of observational studies across populations and time periods; however, it is currently required due to the difficulties in diagnosing neurocysticercosis. Studies discussed that a lack of data was a key limitation and their results likely underestimate the true burden of T. solium. Methods to calculate disability-adjusted life years varied across studies with differences in approaches to time discounting, age weighting, years of life lost, and years of life lived with disability. Such differences limit the ability to compare estimates between studies.

Conclusions

This review illustrates the complexities associated with T. solium burden of disease studies and highlights the potential need for a burden of disease reporting framework. The burden of T. solium is likely underestimated due to the challenges in diagnosing neurocysticercosis and a lack of available data. Advancement in diagnostics, further observational studies, and new approaches to parameterising disease models are required if estimates are to improve.

Development of a dose-response model for porcine cysticercosis

Taenia solium is an important cause of acquired epilepsy worldwide and remains endemic in Asia, Africa, and Latin America. Transmission of this parasite is still poorly understood despite the design of infection experiments to improve our knowledge of the disease, with estimates for critical epidemiological parameters, such as the probability of human-to-pig infection after exposure to eggs, still lacking. In this paper, a systematic review was carried out and eight pig infection experiments were analyzed to describe the probability of developing cysts. These experiments included different pathways of inoculation: with ingestion of proglottids, eggs, and beetles that ingested eggs, and direct injection of activated oncospheres into the carotid artery. In these experiments, different infective doses were used, and the numbers of viable and degenerated cysts in the body and brain of each pig were registered. Five alternative dose-response models (exponential, logistic, log-logistic, and exact and approximate beta-Poisson) were assessed for their accuracy in describing the observed probabilities of cyst development as a function of the inoculation dose. Dose-response models were developed separately for the presence of three types of cysts (any, viable only, and cysts in the brain) and considered for each of the four inoculation methods ("Proglottids", "Eggs", "Beetles" and "Carotid"). The exact beta-Poisson model best fit the data for the three types of cysts and all relevant exposure pathways. However, observations for some exposure pathways were too scarce to reliably define a dose-response curve with any model. A wide enough range of doses and sufficient sample sizes was only found for the "Eggs" pathway and a merged "Oral" pathway combining the "Proglottids", "Eggs" and "Beetles" pathways. Estimated parameter values from this model suggest that a low infective dose is sufficient to result in a 50% probability for the development of any cyst or for viable cyst infections. Although this is a preliminary model reliant on a limited dataset, the parameters described in this manuscript should contribute to the design of future experimental infections related to T. solium transmission, as well as the parameterization of simulation models of transmission aimed at informing control.

Taenia solium taeniasis/cysticercosis: From parasite biology and immunology to diagnosis and control

Infection with the pork tapeworm (Taenia solium) is responsible for a substantial global burden of disease, not only restricted to its impact on human health, but also resulting in a considerable economic burden to smallholder pig farmers due to pig cysticercosis infection. The life-cycle, parasitology and immunology of T. solium are complex, involving pigs (the intermediate host, harbouring the larval metacestode stage), humans (the definitive host, harbouring the adult tapeworm, in addition to acting as accidental intermediate hosts) and the environment (the source of infection with eggs/proglottids). We review the parasitology, immunology, and epidemiology of the infection associated with each of the T. solium life-cycle stages, including the pre-adult/adult tapeworm responsible for human taeniasis; post-oncosphere and cysticercus associated with porcine and human cysticercosis, and the biological characteristics of eggs in the environment. We discuss the burden associated, in endemic settings, with neurocysticercosis (NCC) in humans, and the broader cross-sectoral economic impact associated both with NCC and porcine cysticercosis, the latter impacting food-value chains. Existing tools for diagnostics and control interventions that target different stages of the T. solium transmission cycle are reviewed and their limitations discussed. Currently, no national T. solium control programmes have been established in endemic areas, with further work required to identify optimal strategies according to epidemiological setting. There is increasing evidence suggesting that cross-sectoral interventions which target the parasite in both the human and pig host provide the most effective approaches for achieving control and ultimately elimination. We discuss future avenues for research on T. solium to support the attainment of the goals proposed in the revised World Health Organisation neglected tropical diseases roadmap for 2021-2030 adopted at the 73rd World Health Assembly in November 2020.

The potential of diagnostic point-of-care tests (POCTs) for infectious and zoonotic animal diseases in developing countries: Technical, regulatory and sociocultural considerations

Remote and rural communities in low‐ and middle‐income countries (LMICs) are disproportionately affected by infectious animal diseases due to their close contact with livestock and limited access to animal health personnel). However, animal disease surveillance and diagnosis in LMICs is often challenging, and turnaround times between sample submission and diagnosis can take days to weeks. This diagnostic gap and subsequent disease under‐reporting can allow emerging and transboundary animal pathogens to spread, with potentially serious and far‐reaching consequences. Point‐of‐care tests (POCTs), which allow for rapid diagnosis of infectious diseases in non‐laboratory settings, have the potential to significantly disrupt traditional animal health surveillance paradigms in LMICs. This literature review sought to identify POCTs currently available for diagnosing infectious animal diseases and to determine facilitators and barriers to their use and uptake in LMICs. Results indicated that some veterinary POCTs have been used for field‐based animal disease diagnosis in LMICs with good results. However, many POCTs target a small number of key agricultural and zoonotic animal diseases, while few exist for other important animal diseases. POCT evaluation is rarely taken beyond the laboratory and into the field where they are predicted to have the greatest impact, and where conditions can greatly affect test performance. A lack of mandated test validation regulations for veterinary POCTs has allowed tests of varying quality to enter the market, presenting challenges for potential customers. The use of substandard, improperly validated or unsuitable POCTs in LMICs can greatly undermine their true potential and can have far‐reaching negative impacts on disease control. To successfully implement novel rapid diagnostic pathways for animal disease in LMICs, technical, regulatory, socio‐political and economic challenges must be overcome, and further research is urgently needed before the potential of animal disease POCTs can be fully realized.

Perceptions and acceptability of piloted Taenia solium control and elimination interventions in two endemic communities in eastern Zambia

Infections with Taenia solium cause significant public health and economic losses worldwide. Despite effective control tools, long-term sustained control/elimination of the parasite has not been demonstrated to date. Success of intervention programs is dependent on their acceptability to local communities. Focus group discussions (FGDs) and questionnaires (QS) were conducted in two study communities in eastern Zambia to assess local perceptions and acceptance of two piloted intervention strategies: one targeting pigs only ('control' study arm), and one integrated human- and pig-based ('elimination') strategy. QS (n = 227) captured data regarding participation in project activities, knowledge and perceptions of T. solium and of the interventional drugs used in the study. FGDs (n = 18) discussed perceived advantages and disadvantages of the interventions and of the project's delivery and value. QS data revealed 67% of respondents participated in at least one educational activity, and 80% correctly identified at least one disease targeted by the education. All elimination study arm respondents (n = 113) had taken the human treatment, and 98% intended to do so next time. Most (70%) indicated willingness to pay for future treatments (median 0.20 USD per dose). Of pig-owning respondents, 11/12 (92%) had allowed their pigs to be treated/vaccinated and all intended to do so again next time. Four pig owners indicated willingness to pay 0.10-0.50 USD per dose of treatment or vaccine. FGD feedback revealed positive perceptions of interventions; people reported improved health in themselves and their pigs, and fewer cysticerci in pork. Latrine use, hand washing, meat inspection and proper cooking of pork had reportedly increased since the program's inception. Preliminary assessment indicates that the piloted intervention methods are generally acceptable to the communities. The reported willingness of many respondents to pay for the medications would contribute to the feasibility of long-term, government-led T. solium intervention programs in future.

Currently Available Monitoring and Surveillance Systems for Taenia spp., Echinococcus spp., Schistosoma spp., and Soil-Transmitted Helminths at the Control/Elimination Stage: A Systematic Review

An increasing global focus on neglected tropical diseases (NTDs) has resulted in the set up of numerous control and elimination activities worldwide. This is partly true for Taenia solium taeniasis/cysticercosis, the most important foodborne parasitic infection. Despite substantial progress, adequate monitoring and surveillance (M&S) are required to sustain a status of control/elimination. This is often lacking, especially for T. solium. Therefore, the objective was to conduct a systematic literature review of the currently available M&S systems at the control/elimination stage of the four top-ranked helminth NTDs. Specifically, Taenia spp., Echinococcus spp., Schistosoma spp., and soil-transmitted helminths (STHs) were considered to determine if there are any similarities between their M&S systems and whether certain approaches can be adopted from each other. The systematic review demonstrated that rigorous M&S systems have been designed for the control/elimination stage of both STHs and schistosomiasis, particularly in China. On the other hand, a concept of M&S for Taenia spp. and Echinococcus spp. has not been fully developed yet, due to a lack of epidemiological data and the fact that many endemic countries are far away from reaching control/elimination. Moreover, accurate diagnostic tools for all four diseases are still imperfect, which complicates proper M&S. Finally, there is an urgent need to develop and harmonize/standardize M&S activities in order to reliably determine and compare the epidemiological situation worldwide.

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

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.

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

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.

Control of Taenia solium; A Case for Public and Private Sector Investment

The zoonotic helminth T. solium is one of the leading causes of acquired epilepsy in endemic countries, resulting in a high burden both in human health and social stigma of affected people (1-3). In 2012 T. solium was highlighted as a priority for control in the World Health Assembly resolution 66.12 (4). Despite a call for validated control strategies by 2015 and a "Tool Kit" of control options being available, relatively few examples of successfully implemented and sustainable control programs are available (5-7). A minimal control strategy focusing solely on the porcine host has also been proposed although the cost-effectiveness of such has yet to be explored (8). Although acknowledgment has been made of the need for initiatives to be sustainable, we are yet to see sufficient consideration of the balance between the provision of public and private goods, and the need for engagement of the people and organizations in the pork value chains within T. solium control strategies. We utilized a food chain risk analysis model to determine the incremental cost-effectiveness ratio (ICER) in terms of $/infective meal avoided, of combining a pharmaceutical intervention in pigs with strengthened meat hygiene services. The addition of a vaccination and treatment protocol, at an additional 10.3% cost, was illustrated to have the potential to improve the ICER of improving meat inspection by 74.6%. The vaccination and treatment protocol also had the potential to reduce the losses borne by the pork industry of condemned meat by 66%, highlighting the potential to leverage private sector investment in T. solium control.

Effects of 'The Vicious Worm' educational tool on Taenia solium knowledge retention in Zambian primary school students after one year

BACKGROUND

Taenia solium is a neglected zoonotic parasite endemic throughout many low-income countries worldwide, including Zambia, where it causes human and pig diseases with high health and socioeconomic burdens. Lack of knowledge is a recognized risk factor, and consequently targeted health educational programs can decrease parasite transmission and disease occurrence in endemic areas. Preliminary assessment of the computer-based education program 'The Vicious Worm' in rural areas of eastern Zambia indicated that it was effective at increasing knowledge of T. solium in primary school students. The aim of this study was to evaluate the impact of 'The Vicious Worm' on knowledge retention by re-assessing the same primary school students one year after the initial education workshops.

METHODOLOGY/PRINCIPAL FINDINGS

Follow-up questionnaires were administered in the original three primary schools in eastern Zambia in 2017, 12 months after the original workshops. In total, 86 pupils participated in the follow-up sessions, representing 87% of the initial workshop respondents. Knowledge of T. solium at 'follow-up' was significantly higher than at the initial 'pre' questionnaire administered during the Vicious Worm workshop that took place one year earlier. While some specifics of the parasite's life cycle were not completely understood, the key messages for disease prevention, such as the importance of hand washing and properly cooking pork, remained well understood by the students, even one year later.

CONCLUSIONS/SIGNIFICANCE

Results of this study indicate that 'The Vicious Worm' may be an effective tool for both short- and long-term T. solium education of rural primary school students in Zambia. Inclusion of educational workshops using 'The Vicious Worm' could be recommended for integrated cysticercosis control/elimination programs in sub-Saharan Africa, particularly if the content is simplified to focus on the key messages for prevention of disease transmission.

Strategies for tackling Taenia solium taeniosis/cysticercosis: A systematic review and comparison of transmission models, including an assessment of the wider Taeniidae family transmission models

Background

The cestode Taenia solium causes the neglected (zoonotic) tropical disease cysticercosis, a leading cause of preventable epilepsy in endemic low and middle-income countries. Transmission models can inform current scaling-up of control efforts by helping to identify, validate and optimise control and elimination strategies as proposed by the World Health Organization (WHO).

Methodology/Principal findings

A systematic literature search was conducted using the PRISMA approach to identify and compare existing T. solium transmission models, and related Taeniidae infection transmission models. In total, 28 modelling papers were identified, of which four modelled T. solium exclusively. Different modelling approaches for T. solium included deterministic, Reed-Frost, individual-based, decision-tree, and conceptual frameworks. Simulated interventions across models agreed on the importance of coverage for impactful effectiveness to be achieved.

Other Taeniidae infection transmission models comprised force-of-infection (FoI), population-based (mainly Echinococcus granulosus) and individual-based (mainly E. multilocularis) modelling approaches. Spatial structure has also been incorporated (E. multilocularis and Taenia ovis) in recognition of spatial aggregation of parasite eggs in the environment and movement of wild animal host populations.

Conclusions/Significance

Gaps identified from examining the wider Taeniidae family models highlighted the potential role of FoI modelling to inform model parameterisation, as well as the need for spatial modelling and suitable structuring of interventions as key areas for future T. solium model development. We conclude that working with field partners to address data gaps and conducting cross-model validation with baseline and longitudinal data will be critical to building consensus-led and epidemiological setting-appropriate intervention strategies to help fulfil the WHO targets.

Taenia solium infection in humans (taeniosis and neurocysticercosis) and pigs (cysticercosis) presents a significant global public health and economic challenge. The World Health Organization has called for validated strategies and wider consensus on which strategies are suitable for different epidemiological settings to support successful T. solium control and elimination efforts. Transmission models can be used to inform these strategies. Therefore, a modelling review was undertaken to assess the current state and gaps relating to T. solium epidemiological modelling. The literature surrounding models for other Taeniidae family infections was also considered, identifying approaches to aid further development of existing T. solium models. A variety of different modelling approaches have been used for T. solium including differences in structural and parametric assumptions associated with T. solium transmission biology. Despite these differences, all models agreed on the importance of coverage on intervention effectiveness. Other Taeniidae family models highlighted the need for incorporating spatial structure when necessary to capture aggregation of transmission stages in the environment and movement of animal hosts.

Taenia solium control in Zambia: The potholed road to success

The taeniosis/cysticercosis neglected zoonotic disease complex is caused by Taenia solium, and is associated with significant economic and public health impacts. This paper reviews the current knowledge on T. solium in Zambia and the control strategies already studied, covering almost 20 years of research, and explores the way forward. Studies on occurrence of porcine cysticercosis indicated very high prevalences, ranging from 15 to 34% based on detection of circulating antigens, and of 46% to 68% based on full carcass dissection in slaughter age pigs. Taeniosis prevalences have been reported to range from 6.3% to 12% based on copro-Ag-ELISA. Human cysticercosis prevalence results ranged from 5.8% to 13% based on serum Ag-ELISA, and from 34% to 39% based on sero-antibody detection. Later on, a study in people with epilepsy suggested neurocysticercosis to be the single most important cause of epilepsy in this T. solium endemic area, with 57% of the people with active epilepsy diagnosed with probable or definite neurocysticercosis. While the need to reduce the disease burden of T. solium in Zambia is obvious, the exact short and long term goals, and the strategies to achieve these goals, are not clear. We have selected the most promising control/elimination strategies from reviews and assessed these for feasibility via discussions with local stakeholders from both medical and veterinary sectors. The proposed measures were evaluated using the newly developed agent-based disease transmission model, cystiSim and optimised using Zambian demographic and disease data. As a control option, yearly porcine treatments were selected as best option, while the preferred strategy for elimination was determined to be the combination of human and porcine mass drug administration combined with porcine vaccination of all eligible people and pigs, in a schedule of six iterations of four monthly interventions. These interventions are currently being field tested, combined with education. Several other hurdles to control, such as cost and socio-political factors and the need for an improved advocacy and awareness creation are discussed.