Fecal samples from 194 individuals living in an area of Brazil endemic for Schistosoma mansoni were analyzed by a polymerase chain reaction (PCR) and the Kato-Katz parasitologic examination. Statistical analysis of the results showed a kappa index of 0.8 between the two methods. The prevalence of infection was 30.9% in three fecal samples examined by the Kato-Katz method, but 38.1% in one fecal sample examined by the PCR technique. Repeated survey of discordant results showed that five (41.6%) of 12 parasitologically negative cases for which PCR gave positive results were misdiagnosed by Kato-Katz examinations. The PCR technique showed a sensitivity of 96.7% and a specificity of 88% when the parasitologic examination was used as the reference test. The efficacy of cure with praziquantel was 87.8% in three parasitologic stool examinations and 75.6% in one PCR survey. These results demonstrate that the PCR assay might be a valuable alternative for diagnosing Schistosoma infections.

BackgroundA PCR-enzyme-linked immunosorbent assay (PCR-ELISA) was developed to overcome the need for sensitive techniques for the efficient diagnosis of Schistosoma infection in endemic settings with low parasitic burden.Methodology/Principal FindingsThis system amplifies a 121-base pair tandem repeat DNA sequence, immobilizes the resultant 5′ biotinylated product on streptavidin-coated strip-well microplates and uses anti-fluorescein antibodies conjugated to horseradish peroxidase to detect the hybridized fluorescein-labeled oligonucleotide probe. The detection limit of the Schistosoma PCR-ELISA system was determined to be 1.3 fg of S. mansoni genomic DNA (less than the amount found in a single cell) and estimated to be 0.15 S. mansoni eggs per gram of feces (fractions of an egg). The system showed good precision and genus specificity since the DNA target was found in seven Schistosoma DNA samples: S. mansoni, S. haematobium, S. bovis, S. intercalatum, S. japonicum, S. magrebowiei and S. rhodaini. By evaluating 206 patients living in an endemic area in Brazil, the prevalence of S. mansoni infection was determined to be 18% by examining 12 Kato-Katz slides (41.7 mg/smear, 500 mg total) of a single fecal sample from each person, while the Schistosoma PCR-ELISA identified a 30% rate of infection using 500-mg of the same fecal sample. When considering the Kato-Katz method as the reference test, artificial sensitivity and specificity rates of the PCR-ELISA system were 97.4% and 85.1%, respectively. The potential for estimating parasitic load by DNA detection in feces was assessed by comparing absorbance values and eggs per gram of feces, with a Spearman correlation coefficient of 0.700 (P<0.0001).Conclusions/SignificanceThis study reports the development and field evaluation of a sensitive Schistosoma PCR-ELISA, a system that may serve as an alternative for diagnosing Schistosoma infection.

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