Next step towards point-of-care molecular diagnosis of female genital schistosomiasis (FGS): evaluation of an instrument-free LAMP procedure

  • van Bergen K
  • Brienen E
  • Randrianasolo B
  • et al.
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Abstract

Detection of Schistosoma spp. DNA in gynaecological samples by quantitative real-time polymerase chain reaction (qPCR) is considered to be the reference diagnostic test for female genital schistosomiasis (FGS). However, qPCR needs expensive laboratory procedures and highly trained technicians. Loop-mediated amplification (LAMP) is a more field-friendly isothermal procedure for the detection of parasite-specific DNA, but it still requires electrically powered equipment. Here, we validated a Schistosoma haematobium -specific Sh-LAMP procedure and tested a fully instrument-free isothermal amplification using a novel low-cost, and reusable Temperature-cup (T-cup) device. Specific primers were selected based on published assays, targeting the ribosomal intergenic spacer (IGS) region of S. haematobium . Technical validation of the IGS-Sh-LAMP was performed using 20 negative controls, including DNA extracts of soil-transmitted helminths and S. mansoni , and a 10-fold dilution series (10 0 –10 −3 ) of DNA extracted from a single S. haematobium egg (n=4). For clinical validation, the IGS-Sh-LAMP was tested on 125 DNA samples extracted from vaginal swabs of a previous FGS study in Madagascar. Results were compared with the quantification cycle value (Cq) of the standard ITS-2 targeting qPCR. Single S. haematobium egg DNA up to a 10 –2 dilution and an ITS-2 Cq <35 tested positive in the IGS-Sh-LAMP. The specificity was found to be excellent (100%). In the clinical samples, IGS-Sh-LAMP showed comparable results with the qPCR, with 35.2% and 33.6% positives, respectively, and a concordance of 79.2% (99/125). Of the 12 false-negatives, 5 corresponded to the 7 qPCR positive samples with very low DNA levels (Cq ≥35). On the other hand, IGS-Sh-LAMP detected 14 additional cases that were not detected by qPCR. The T-cup IGS-Sh-LAMP performance was evaluated in a representative sub-selection (n=10) of IGS-Sh-LAMP positive clinical samples. The T-cup IGS-Sh-LAMP was found to be a very user-friendly method, but in different runs, it missed 1 to 4 of the 10 IGS-Sh-LAMP positive samples, specifically those with a low DNA load. Our results show that the IGS-Sh-LAMP is a suitable alternative to the ITS-2 qPCR for the diagnosis of FGS in gynaecological samples, with high potential for the T-cup as a fully instrument-free isothermal amplification device for point-of-care diagnosis in low-resource settings.

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van Bergen, K. J. M., Brienen, E. A. T., Randrianasolo, B. S., Ramarokoto, C. E., Leutscher, P., Kjetland, E. F., … van Lieshout, L. (2024). Next step towards point-of-care molecular diagnosis of female genital schistosomiasis (FGS): evaluation of an instrument-free LAMP procedure. Frontiers in Parasitology, 3. https://doi.org/10.3389/fpara.2024.1297310

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