Conventional parasitology and DNA-based diagnostic methods for onchocerciasis elimination programmes

Area of Science:

• Medical Parasitology
• Molecular Diagnostics
• Tropical Public Health

Background:

• Current diagnostics for Onchocerca volvulus, including skin snip microscopy and nodule palpation, exhibit low sensitivity.
• There is a critical need for more sensitive diagnostic tools to effectively monitor onchocerciasis elimination programs and diagnose individual cases.

Purpose of the Study:

• To develop and evaluate a sensitive probe-based quantitative polymerase chain reaction (qPCR) assay for detecting Onchocerca volvulus DNA.
• To compare the diagnostic performance of the new qPCR assay against conventional methods in an endemic population.

Main Methods:

• A probe-based qPCR assay was developed to detect Onchocerca volvulus DNA.
• The assay was validated using dried skin snip pairs from 369 individuals in an endemic area of eastern Côte d'Ivoire.
• Results were compared with routine skin snip microscopy and nodule palpation.

Main Results:

• Onchocerciasis prevalence determined by qPCR was 56.9%, significantly higher than microscopy (26.0%) and nodule palpation (37.9%).
• The combined use of qPCR, microscopy, and nodule palpation identified a 72.9% infection prevalence, exceeding conventional methods (53.1%).
• Notably, the qPCR assay yielded negative results for 54 individuals with palpable nodules, indicating potential limitations or complexities in parasite distribution.

Conclusions:

• The developed qPCR assay demonstrates superior sensitivity for detecting Onchocerca volvulus infections compared to traditional methods.
• qPCR shows promise as a valuable tool for identifying residual infections in onchocerciasis elimination programs, especially as prevalence declines.
• Further investigation is warranted to understand discrepancies between qPCR and nodule palpation results.