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The following is a summary of “Improved NAAT assay for the diagnosis of onchocerciasis and its use for detection of circulating cell free DNA,” published in the September 2024 issue of Infectious Disease by Bennuru et al.
Researchers conducted a retrospective study to develop a compassionate and specific diagnostic tool for onchocerciasis suitable for surveillance and xenomonitoring, considering its co-endemicity with other filariae.
They designed qPCR assays with NGS data for 15 highly repeated targets from O. volvulus (Ov) and 11 from O. ochengi (Oo). The 2 repeats, Ov15R and Ov16R from Ov and OoR1 and OoR5 from Oo, were selected for further testing.
The results showed that Ov15R and Ov16R had similar analytical sensitivity, with limits of detection (LOD) at 1 fg and specificity approaching 100%. They used DNA from skin snips, Ov16R identified 17 additional Ov infections compared to O-150, while Ov16R failed to detect ccfDNA in plasma; 1ml urine samples from individuals with Ov-infection were variably positive for ccfDNA. Plasma ccfDNA levels were measurable as early as 12-24 hours after treatment. A chitosan-based filter technique captured ccfDNA from 1-15 ml of urine. Interestingly, Ov15R, Ov16R, and O-150 mapped to the same genome region, leading to a redesigned O-150R assay that performs similarly to Ov15R/Ov16R.
They concluded that these assays significantly improve the detection of Ov DNA and can be easily adapted to a field-friendly isothermal format.
Source: academic.oup.com/jid/advance-article/doi/10.1093/infdis/jiae462/7765955
