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.