Real-time PCR for diagnosis of imported schistosomiasis

Abstract

Background

The diagnosis of schistosomiasis currently relies on microscopic detection of schistosome eggs in stool or urine samples and serological assays. The poor sensitivity of standard microscopic procedures performed in routine laboratories, makes molecular detection methods of increasing interest. The aim of the study was to evaluate two in-house real-time Schistosoma PCRs, targeting respectively S. mansoni [Sm] and S. haematobium [Sh] in excreta, biopsies and sera as potential tools to diagnose active infections and to monitor treatment efficacy.

Methods

Schistosoma PCRs were performed on 412 samples (124 urine, 86 stools, 8 biopsies, 194 sera) from patients with suspected schistosomiasis, before anti-parasitic treatment. Results were compared to microscopic examination and serological assays (enzyme-linked immunosorbent assay (ELISA), indirect haemagglutination (HA) and Western Blot (WB) assay).

Results

Compared to microscopy, PCRs significantly increased the sensitivity of diagnosis, from 4% to 10.5% and from 33.7% to 48.8%, for Sh in urine and Sm in stools, respectively. The overall sensitivity of PCR on serum samples was 72.7% and reached 94.1% in patients with positive excreta (microscopy). The specificity of serum PCR was 98.9%. After treatment, serum PCR positivity rates slowly declined from 93.8% at day 30 to 8.3% at day 360, whereas antibody detection remained positive after 1 year.

Conclusion

Schistosoma PCRs clearly outperform standard microscopy on stools and urine and could be part of reference methods combined with WB-based serology, which remains a gold standard for initial diagnosis. When serological assays are positive and microscopy is negative, serum PCRs provide species information to guide further clinical exploration. Biomarkers such as DNA and antibodies are of limited relevance for early treatment monitoring but serum PCR could be useful when performed at least 1 year after treatment to help confirm a cured infection.

Author summary

Schistosomiasis is one of the most important human parasitic neglected tropical diseases. It is a major source of morbidity and mortality in Africa but also in South America, the Caribbean, the Middle East, and Asia. It is transmitted by skin penetration of schistosome cercariae via contact with freshwater. Schistosoma mansoni and S. haematobium are the most common species and are frequent causes of infection in travelers and migrants returning from endemic areas. Chronic infections with these two species can cause irreversible damage to the liver or genitourinary tract. Diagnosis mainly relies on serological screening and microscopic procedures from urine and stool specimens that can, however, fail to detect low parasite burden and depend on operator competence. So there is a need to improve the detection of this disease. With this retrospective study, we evaluate the accuracy of a specific Schistosoma PCR assay for the diagnosis of schistosomiasis on a large cohort of migrants and travelers returning from endemic areas. Our study showed that PCR, a technique allowing Schistosoma DNA amplification and detection, greatly improved the diagnosis of both parasite species in urine, feces and biopsies. We also demonstrate that the detection of circulating Schistosoma DNA in blood by PCR is useful to confirm schistosomiasis diagnosis, to provide a species identification when the microscopy research is negative and to monitor the treatment efficacy.