Abstract
Skin snip evaluation for onchocerciasis has insufficient sensitivity when skin microfilarial (mf) densities are low, such as following ivermectin treatment. Mf density is suitable for assessing microfilaricidal efficacy but only serves as an indirect indicator of macrofilaricidal activity. We assessed circulating nucleic acids from Onchocerca volvulus as an alternative to skin snips. We screened a plasma sample set of infected individuals followed up at four, 12 and 21 months after microfilaricidal (ivermectin, n = four), macrofilaricidal (doxycycline, n = nine), or combination treatment (n = five). Two parasite-derived miRNAs, cel-miR-71-5p and bma-lin-4, and O-150 repeat DNA were assessed. Highly abundant DNA repeat families identified in the O. volvulus genome were also evaluated. miRNAs were detected in two of 72 plasma samples (2.8%) and two of 47 samples (4.3%) with microfilaridermia using RT-qPCR. O-150 DNA was detected in eight (44.4%) baseline samples by qPCR and the number of positives declined post-treatment. One doxycycline-treated individual remained O-150 positive. However, only 11 (23.4%) samples with microfilaridermia were qPCR-positive. Analysis by qPCR showed novel DNA repeat families were comparatively less abundant than the O-150 repeat. Circulating parasite-derived nucleic acids are therefore insufficient as diagnostic tools or as biomarkers of treatment efficacy for O. volvulus.
Highlights
Onchocerciasis, or “river blindness” is a parasitic disease caused by the filarial worm Onchocerca volvulus
We report here the use of reverse transcription (RT)-qPCR to detect O. volvulus miRNAs lin-4 and miR-71, selected as they have been sequenced in plasma from infected individuals in Cameroon[39], and qPCR to detect O-150 repeat DNA in plasma
This study reports the first use of RT-qPCR and qPCR to detect O. volvulus miRNAs and DNA, respectively, in plasma from individuals in an onchocerciasis-endemic community before and after macrofilaricidal or microfilaricidal treatment
Summary
Onchocerciasis, or “river blindness” is a parasitic disease caused by the filarial worm Onchocerca volvulus. High specificity is required to discriminate between closely related filarial nematodes with overlapping geographic distributions This is relevant in areas co-endemic for O. volvulus and the filarial worm Loa loa, such as in “hypoendemic hotspots”[6], where IVM treatment can cause serious adverse events (SAEs) when L. loa microfilaraemia is high (>30,000 mf/ml)[7]. In these areas, alternative strategies with drugs that are safe to use with loiasis will be required to meet elimination targets[8]. Skin snips are invasive and becoming increasingly unpopular, and the procedure is often refused by endemic communities[23]
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