Abstract
BackgroundMonitoring the success of soil-transmitted helminth (STH) control programs relies on accurate diagnosis and quantitative assessment of infection prevalence and intensity. As preventative chemotherapeutic program coverage for STH expands, the necessity of gaining insights into the relative or comparative sensitivities, in terms of limits of detection (LOD) and egg-recovery-rates (ERR) for microscopy and quantitative polymerase chain reaction qPCR-based diagnostic techniques becomes imperative to inform suitability for their intended use for large scale STH monitoring and treatment efficacy studies.Methodology/Principal findingsThe diagnostic performance in terms of ERR and LOD of the Kato-Katz (KK) thick smear technique, sodium nitrate (NaNO3) faecal floatation (FF) and qPCR for the accurate detection and enumeration of STH eggs were calculated and expressed in eggs per gram (EPG), by experimentally seeding parasite-free human faeces with Ascaris spp., Trichuris spp. and Necator americanus eggs representing low, medium and high intensity infections. The efficiency of NaNO3 flotation was also calculated over a range of specific gravities (SpGr) for the optimum recovery of STH eggs. FF of SpGr 1.30 recovered 62.7%, 11% and 8.7% more Trichuris spp., Necator americanus and Ascaris spp. eggs respectively, than the recommended SpGr of 1.20. All diagnostic methods demonstrated strong direct correlation to the intensity of seeded EPG. KK and FF (SpGr 1.30) resulted in significant lower ERRs compared to qPCR (p <0.05). qPCR demonstrated significantly (p <0.05) greater sensitivity with an ability to detect as little as 5 EPG for all three STH, compared to 50 EPG by KK and FF (SpGr 1.30).Conclusions/SignificanceThis study compares the diagnostic parameters in terms of LOD and ERRs of STHs for the KK, FF and qPCR. These results indicate that the diagnostic performance of qPCR assays should be considered by control programs in the phase that aims to seek confirmation of transmission break and cessation of preventive chemotherapy in low-transmission settings, in line with the control targets of the WHO neglected tropical diseases 2030 Roadmap.
Highlights
Over 1.5 billion people are infected with at least one soil-transmitted helminth (STHs; Ascaris lumbricoides, Necator americanus, Ancylostoma spp. and Trichuris trichiuria) worldwide
In this study we report a comparison of the ERR and limits of detection (LOD) of seeded Ascaris, Trichuris and Necator eggs in parasite-free human faeces using KK, sodium nitrate (NaNO3) faecal floatation (FF) (SpGr 1.20, 1.25, 1.30 and 1.35), and multiplex quantitative PCR (qPCR) that quantifies genera- and species-specific infection intensities using a pre-determined cycle-threshold to eggs per gram (EPG) formula
One-way ANOVA analyses revealed a significant difference among the ERR means for the different specific gravities (SpGr) tested for Ascaris (p = 0.003, R2 0.90), Trichuris (p
Summary
Over 1.5 billion people are infected with at least one soil-transmitted helminth (STHs; Ascaris lumbricoides, Necator americanus, Ancylostoma spp. and Trichuris trichiuria) worldwide. The current global control strategy aims to control morbidity of STHs through large-scale deworming programs using preventive chemotherapy (PC; albendazole or mebendazole) for all at-risk populations (preschool and school children, women of reproductive age). As STH morbidity and transmission are directly related to the infection prevalence and intensity [4], accurate diagnosis and quantitation of infections is paramount for assessing impact and informing control programs. Monitoring the success of soil-transmitted helminth (STH) control programs relies on accurate diagnosis and quantitative assessment of infection prevalence and intensity. As preventative chemotherapeutic program coverage for STH expands, the necessity of gaining insights into the relative or comparative sensitivities, in terms of limits of detection (LOD) and egg-recovery-rates (ERR) for microscopy and quantitative polymerase chain reaction qPCR-based diagnostic techniques becomes imperative to inform suitability for their intended use for large scale STH monitoring and treatment efficacy studies
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