Abstract
Human intestinal schistosomiasis is caused by the blood fluke, Schistosoma mansoni. With intensified efforts to control schistosomiasis by mass drug administration using praziquantel (PZQ), there is an urgent need to have accessible, quality-assured diagnostic tests for case detection and disease surveillance and for monitoring efficacy of treatment and other interventions. Current diagnostic tools are limited by suboptimal sensitivity, slow turn-around-time, affordability, and inability to distinguish current from past infections. We describe a simple and rapid diagnostic assay, based on the loop-mediated isothermal amplification (LAMP) technology for diagnosis of S. mansoni infection in human faecal samples. The LAMP primers used in this assay were previously described and they target a 121-bp DNA repeat sequence in S. mansoni. The LAMP assay was optimized at an isothermal temperature of 63°C for 1 hour. The amplified DNA was either visualized under ultraviolet light after electrophoresis or by directly observing the color change after staining the amplicons with CYBR Green dye. The LAMP assay was evaluated against the microscopy-based procedure and the results were analysed using Cohen's kappa coefficient to determine the degree of agreement between the two techniques. The LAMP assay reliably detected S. mansoni ova DNA in faecal samples and parasite DNA in amounts as low as 32fg. When the assay was tested for specificity against other faecal-based soil-transmitted helminths (STH), no cross-reactivity was observed. The LAMP assay was superior to the Kato-Katz assay with a 97% specificity; a high positivity score reliably detecting S. mansoni and a Kappa Coefficient of 0.9 suggested an exceptional agreement between the two techniques. The LAMP assay developed has great potential for application in field settings to support S. mansoni control and elimination campaigns.
Highlights
Human schistosomiasis is a snail-borne parasitic infection caused by blood flukes in the genus Schistosoma and is among the neglected tropical diseases (NTDs) targeted for elimination [1]
As schistosomiasis control efforts intensify in the endemic areas and become effective, prevalence and intensities of infection will most likely drastically reduce, and so more sensitive diagnostic tests will become necessary for case detection, especially, in low intensity transmission areas or for evaluating efficacy of chemotherapy and disease surveillance in schistosomiasis control programs [5]
A laboratory maintained isolate of S. mansoni originally obtained from a naturally infected patient from Kisumu, western Kenya, and which is routinely maintained in the laboratory at the Kenya Medical Research Institute (KEMRI) in Nairobi through Swiss albino mice and Biomphalaria sudanica snails was used as a test parasite in the development and optimization of the loop-mediated isothermal amplification (LAMP) assay for detection of S. mansoni infection in faecal samples
Summary
Human schistosomiasis is a snail-borne parasitic infection caused by blood flukes in the genus Schistosoma and is among the neglected tropical diseases (NTDs) targeted for elimination [1]. It remains a major public health problem in the tropical and subtropical regions of the world, with an estimated 207 million people infected worldwide, mostly children, and another 779 million people being at risk of becoming infected [2]. As schistosomiasis control efforts intensify in the endemic areas (with renewed interest in the control of neglected tropical diseases) and become effective, prevalence and intensities of infection will most likely drastically reduce, and so more sensitive diagnostic tests will become necessary for case detection, especially, in low intensity transmission areas or for evaluating efficacy of chemotherapy and disease surveillance in schistosomiasis control programs [5]. Microscopy is the gold standard for diagnosis of S. mansoni but it is not sensitive enough to detect low intensity infections; it is tedious and cumbersome to perform and requires expertise to make a diagnosis
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