Ring-Screening to Control Endemic Transmission of Taenia solium

O’Neal, Seth E.; Moyano, Luz M.; Ayvar, Viterbo; Rodríguez, Silvia; Gavidia, C César; Wilkins, Patricia P.; Gilman, Robert H.; Garcı́a, Héctor H.; González, Armando E.

doi:10.1371/journal.pntd.0003125

Cited by 39 publications

(60 citation statements)

References 30 publications

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“…Nonetheless, if the greater sensitivity of ultrasound represents a true difference, it could have an impact on ring interventions given the high reproductive capacity of the adult stage tapeworm and the potential for an untreated case to reverse control gains. In a recent investigation that allocated treatment rings based on tongue-positivity in pigs, the prevalence of taeniasis at study end was 1.4% in the treatment arm [16]. While this was significantly less than the prevalence in the control arm (2.5%), the majority of remaining taeniasis carriers went untreated because they did not fall into treatment rings, suggesting a potential underdiagnosis of heavily infected pigs in this trial.…”

Section: Discussionmentioning

confidence: 81%

“…Since ultrasonography and tongue examination have poor sensitivity at lower cyst burdens, neither is an adequate screening tool for evaluating food safety or for monitoring progress of control programs. Results from several necropsy studies in endemic villages have shown that the vast majority of pigs infected with cysticercosis have less than 10 cysts in the entire carcass [16–18]. Neither ultrasonography nor tongue examination was able to accurately diagnose pigs with burdens of infection less than 100 cysts, detecting just 8% (3/36) and 3% (1/36) of these infected pigs respectively.…”

Section: Discussionmentioning

confidence: 99%

“…However, ultrasonography could prove useful for applications in which detection of heavily infected pigs is the goal. One such application is a control intervention known as “ring-strategy”, which involves screening and treatment of humans and pigs for taeniasis and cysticercosis, respectively, if they live within 100 meters of a pig heavily infected with cysticerci [15, 16]. The working assumption of this approach is that pigs with hundreds or thousands of infecting cysts have experienced repeated or intense exposure to T .…”

Section: Introductionmentioning

confidence: 99%

“…Studies of ring-strategy have relied on tongue examination of pigs to diagnose heavy cyst infection [16,18]. This method involves visual inspection and palpation of the inferior surface of the tongue in live pigs, and was traditionally performed by local buyers experienced at screening pigs prior to sale at market.…”

Section: Introductionmentioning

confidence: 99%

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Assessing Ultrasonography as a Diagnostic Tool for Porcine Cysticercosis

et al. 2017

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BackgroundTaenia solium inflicts substantial neurologic disease and economic losses on rural communities in many developing nations. “Ring-strategy” is a control intervention that targets treatment of humans and pigs among clusters of households (rings) that surround pigs heavily infected with cysticerci. These pigs are typically identified by examining the animal’s tongue for cysts. However, as prevalence decreases in intervened communities, more sensitive methods may be needed to identify these animals and to maintain control pressure. The purpose of this study was to evaluate ultrasonography as an alternative method to detect pigs heavily infected with T. solium cysts.Methodology/Principal FindingsWe purchased 152 pigs representing all seropositive animals villagers were willing to sell from eight communities (pop. 2085) in Piura, Peru, where T. solium is endemic. Tongue and ultrasound examinations of the fore and hind-limbs were performed in these animals, followed by necropsy with fine dissection as gold standard to determine cyst burden. We compared the sensitivity and specificity of ultrasonography with tongue examination for their ability to detect heavy infection (≥ 100 viable cysts) in pigs. Compared to tongue examination, ultrasonography was more sensitive (100% vs. 91%) but less specific (90% vs. 98%), although these differences were not statistically significant. The greater sensitivity of ultrasound resulted in detection of one additional heavily infected pig compared to tongue examination (11/11 vs. 10/11), but resulted in more false positives (14/141 vs. 3/141) due to poor specificity.Conclusions/SignificanceUltrasonography was highly sensitive in detecting heavily infected pigs and may identify more rings for screening or treatment compared to tongue examination. However, the high false positive rate using ultrasound would result in substantial unnecessary treatment. If specificity can be improved with greater operator experience, ultrasonography may benefit ring interventions where control efforts have stalled due to inadequate sensitivity of tongue examination.

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Section: Discussionmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Assessing Ultrasonography as a Diagnostic Tool for Porcine Cysticercosis

et al. 2017

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“…This "bottom-up" structure allows for the modeler to easily manipulate the behaviors or the modeled environment and observe the emergent patterns that are produced by such manipulations. In the context of T. solium transmission, this structure facilitates application of the model to a variety of transmissions settings, and allows for testing a wide range of available control strategies, including spatially targeted strategies (e.g., "Ring Strategy" [28]), and other behavioral and structural interventions.…”

Section: Introductionmentioning

confidence: 99%

Understanding transmission and control of the pork tapeworm with CystiAgent: a spatially explicit agent-based model

Pray¹,

Wakeland

Pan

et al. 2020

Preprint

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BackgroundThe pork tapeworm (Taenia solium) is a serious public health problem in rural low-resource areas of Latin America, Africa, and Asia, where the associated conditions of nuerocysticercosis (NCC) and porcine cysticercosis cause substantial health and economic harms. An accurate and validated transmission model for T. solium would serve as an important new tool for control and elimination, as it would allow for comparison of available intervention strategies, and prioritization of the most effective strategies for control and elimination efforts. MethodsWe developed a spatially-explicit agent-based model (ABM) for T. solium (“CystiAgent”) that differs from prior T. solium models by including a spatial framework and behavioral parameters such as pig roaming, open human defecation, and human travel. In this article, we introduce the structure and function of the model, describe the data sources used to parameterize the model, and apply sensitivity analyses (Latin hypercube sampling–partial rank correlation coefficient (LHS-PRCC)) to evaluate model parameters. ResultsLHS-PRCC analysis of CystiAgent found that the parameters with the greatest impact on model uncertainty were the roaming range of pigs, the infectious duration of human taeniasis, use of latrines, and the set of “tuning” parameters defining the probabilities of infection in humans and pigs given exposure to T. solium.ConclusionsCystiAgent is a novel ABM that has the ability to model spatial and behavioral features of T. solium transmission not available in other models. There is a small set of impactful model parameters that contribute uncertainty to the model and may impact the accuracy of model projections. Field and laboratory studies to better understand these key components of transmission may help reduce uncertainty, while current applications of CystiAgent may consider calibration of these parameters to improve model performance. These results will ultimately allow for improved interpretation of model validation results, and usage of the model to compare available control and elimination strategies for T. solium.

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