The stabilizing effects of the acquired immunity on the schistosomiasis transmission modeling - the sensitivity Analysis

Hyun, Mo Yang; Yang, Ariana Campos

doi:10.1590/s0074-02761998000700009

Cited by 8 publications

(1 citation statement)

References 27 publications

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“…Immunizing the 7-year cohort or the 1-year and 7-year cohorts results in additional substantially declined infection intensities that are further expendable by chemotherapy. Taken together, duration over magnitude of vaccine protection and drug impact [244] is pivotal to determine the optimal age for interventions [240]. It needs to be considered that immunizing the youngest leaves them unprotected later in life, while immunizing schoolchildren protects them once they are at highest risk [239].…”

Section: Though Both Models Show Reductions In Infection Intensities ...mentioning

confidence: 99%

Transmission Modelling for Human Non-Zoonotic Schistosomiasis Incorporating Vaccination: Guiding Decision- and Policymaking

Panzner

2024

Parasitologia

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Schistosomiasis, acquired by skin-penetrating cercariae of dioecious digenean schistosomes during freshwater contact, afflicts nearly 260 and 440 million people with active infections and residual morbidity, respectively. About 10 million women at reproductive age contract schistosomiasis during gestation every year. Acute schistosomiasis is characterized by pre-patent pro-inflammatory CD4+ T-helper 1 or CD4+ Th1/T-helper 17 reactivity against immature schistosomulae. Chronic schistosomiasis is dominated by post-patent anti-inflammatory CD4+ T-helper 2 reactivity against ova epitopes. Flukes co-exist in immunocompetent definitive hosts as they are capable of evading their defense mechanisms. Preventive measures should be complemented by vaccination, inducing long-term protection against transmission, infection, and disease recurrence, given the latest advancements in schistosomal vaccines. Vaccines become pivotal when considering constraints of chemotherapy, i.e., lack of protection against re-infection, and evolving resistance or reduced sensitivity. Transmission models for human non-zoonotic schistosomiasis incorporating vaccination available in PubMed, Embase and Web of Science up to 31 December 2023 are presented. Besides conceptual model differences, predictions meant to guide decision- and policymaking reveal continued worm harboring that facilitates transmission besides residual infections. In addition, increased susceptibility to re-infection and rebound morbidity, both shifted to later life stages following the intervention, are forecasted. Consequently, a vaccination schedule is pivotal that considers the optimal age for initial immunization, i.e., pre-schoolchildren or schoolchildren in a cohort-based or population-based manner, while incorporating potential non-adherers promoting ongoing transmission. Longevity over magnitude of vaccine protection to antigenic schistosomal moieties is crucial. Accounting for pre-acquired immunity from natural exposure, in utero priming in addition to herd immunity, and induced by chemotherapy is crucial. Combining, as a multi-component approach, long-term effects of vaccination with short-term effects of chemotherapy as regular repeated vaccine-linked therapy seems most promising to achieve WHO’s endpoints of transmission elimination and morbidity control.

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Section: Though Both Models Show Reductions In Infection Intensities ...mentioning

confidence: 99%

Transmission Modelling for Human Non-Zoonotic Schistosomiasis Incorporating Vaccination: Guiding Decision- and Policymaking

Panzner

2024

Parasitologia

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Assessing the effects of diagnostic sensitivity on schistosomiasis dynamics

Vilches

Graeff-Teixeira²,

Yang

2021

Journal of Theoretical Biology

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Estimating sensitivity of the Kato-Katz technique for the diagnosis of Schistosoma mansoni and hookworm in relation to infection intensity

et al. 2017

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The Kato-Katz technique is the most widely used diagnostic method in epidemiologic surveys and drug efficacy trials pertaining to intestinal schistosomiasis and soil-transmitted helminthiasis. However, the sensitivity of the technique is low, particularly for the detection of light-intensity helminth infections. Examination of multiple stool samples reduces the diagnostic error; yet, most studies rely on a single Kato-Katz thick smear, thus underestimating infection prevalence. We present a model which estimates the sensitivity of the Kato-Katz technique in Schistosoma mansoni and hookworm, as a function of infection intensity for repeated stool sampling and provide estimates of the age-dependent ‘true’ prevalence. We find that the sensitivity for S. mansoni diagnosis is dominated by missed light infections, which have a low probability to be diagnosed correctly even through repeated sampling. The overall sensitivity strongly depends on the mean infection intensity. In particular at an intensity of 100 eggs per gram of stool (EPG), we estimate a sensitivity of 50% and 80% for one and two samples, respectively. At an infection intensity of 300 EPG, we estimate a sensitivity of 62% for one sample and 90% for two samples. The sensitivity for hookworm diagnosis is dominated by day-to-day variation with typical values for one, two, three, and four samples equal to 50%, 75%, 85%, and 95%, respectively, while it is only weakly dependent on the mean infection intensity in the population. We recommend taking at least two samples and estimate the ‘true’ prevalence of S. mansoni considering the dependence of the sensitivity on the mean infection intensity and the ‘true’ hookworm prevalence by taking into account the sensitivity given in the current study.

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The stabilizing effects of the acquired immunity on the schistosomiasis transmission modeling - the sensitivity Analysis

Cited by 8 publications

References 27 publications

Transmission Modelling for Human Non-Zoonotic Schistosomiasis Incorporating Vaccination: Guiding Decision- and Policymaking

Transmission Modelling for Human Non-Zoonotic Schistosomiasis Incorporating Vaccination: Guiding Decision- and Policymaking

Assessing the effects of diagnostic sensitivity on schistosomiasis dynamics

Estimating sensitivity of the Kato-Katz technique for the diagnosis of Schistosoma mansoni and hookworm in relation to infection intensity

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