Assessing the marginal error in diagnosis and cure of Schistosoma mansoni in areas of low endemicity using Percoll and PCR techniques

Abstract

Summaryobjective The Kato-Katz technique misses a proportion of low-intensity schistosomiasis cases. We set out to estimate the rate of false negative results after Kato-Katz. conclusion The Percoll technique seems to be the technique of choice for diagnosis of S. mansoni in low intensity areas and after treatment.

Diagnosis of Schistosomiasis in Low Endemic Areas

“…PCR methods have shown high sensitivity and specificity for the detection of S. mansoni DNA in stool samples, yet PCR gave negative results among few cases considered sure positives by microscopy (tables1,2) . Similar results were obtained by many authors (13,25,28,29,30) . Table ( (30) .…”

“…It was concluded that for the diagnosis of schistosomiasis in low endemic areas, circulating antigen detection should be considered as a complementary tool rather than a substitute for parasitological examination specially that the detection of CCA in urine and CAA in serum supplies additional information to determine more accurately the "true" prevalence of infection (23,24) . To date, Percoll sedimentation technique was established as the technique of choice for diagnosis of S. mansoni in low intensity conditions and post treatment (25) . This method always gives better and more consistent estimate than the Kato Katz , and efficiently detects low intensity infections up to 4 eggs /gm.…”

“…Table ( (30) . (25) reported that missed cases after PCR were certainly misdiagnosed by the DNA amplification assay due to many factors such as: inhibition of the amplification reaction by fecal compounds and ⁄ or DNA degradation during transportation from the field, variation in egg output and uneven distribution in feces. Oliveira et al(2010) (31) reported that PCR can be an important tool for detecting S. mansoni infection in individuals excreting few eggs in feces.…”

Further evaluation of an updated PCR assay for the detection of Schistosoma mansoni DNA in human stool samples

“…Pontes et al (2002) reported the first use of PCR for the diagnosis of Schistosoma mansoni DNA in faecal samples. High sensitivity and specificity rates were observed by this (Pontes et al 2003) and another group (Allam et al 2009) when compared to routine parasitological examination according to the Kato-Katz method (Katz et al 1972).…”

Diagnosing schistosomiasis: where are we?

“…The authors emphasize that this technique might prove to be useful in low transmission settings due to its high sensitivity (96,7%) compared to the 79% of sensitivity obtained by stool examination, when the criteria for positivity was determined as positivity by any of the direct methods. The sensitivity of this technique was reevaluated in other studies in which it was applied to preselected individuals with low worm burden 77,78 and schistosomiasis positive patients after treatment 79 . Under these specific conditions, both studies confirmed the high sensitivity of the PCR assay.…”