Improving onchocerciasis elimination surveillance: trials of odour baited Esperanza Window Traps to collect black fly vectors and real-time qPCR detection of Onchocerca volvulus in black fly pools

Abstract

Abstract Background Entomological data for onchocerciasis surveillance relies on sampling blackflies through human landing collectors in the field and laboratory testing of the flies for infection using pool screening O-150 PCR-ELISA assay. Both techniques require improvements. This study sought to take promising Esperanza Window Traps (EWT) for blackfly collections and test and optimize them to find alternative carbon dioxide (CO2) mimics, and to test new qPCR methods using mitochondrial DNA targets that have been suggested to improve sensitivity and specificity for Onchocerca volvulus infection in flies. Methods Traps baited with low, medium and high release rates of either 2-butanone or cyclopentanone as CO2 mimics were field tested against traps baited with organically generated CO2 in Guinea savannah, derived savannah, rainforest and montane forest ecological zones in Nigeria. The performance of EWTs baited with CO2 or in combination with 2-butanone (low release) were subsequently evaluated against the human landing collection (HLC). Trap scaling was also pilot tested by comparing double traps to single HLCs. Collected blackflies were used to test detection of O. volvulus in blackflies using Ov ND5 real time PCR (qPCR) in comparison to the conventional pool screening O-150 PCR. Results EWTs baited with 2-butanone caught similar numbers of blackflies to those baited with CO2, while cyclopentanone collected significantly fewer flies in all locations. The low release of 2-butanone was the most effective overall, although HLCs collected higher numbers of blackflies than EWT baited with CO2 either singly or in combination with low release 2-butanone. The combination of two EWTs baited with CO2 and deployed 100 m apart to each other collected similar numbers of flies as one HLC. More blackfly pools were positive for O. volvulus by Ov ND5 qPCR as compared with O-150 PCR in derived savannah (31.15% vs 15.57%), montane forest (11.54% vs 0%) and rainforest (23.08% vs 2.56%), with only one positive pool in Guinea savannah detected by both methods. Conclusion 2-butanone has potential to be used in xenomonitoring as a standardized replacement to organically generated CO2. The positive pools found in foci hitherto considered to have interrupted/eliminated onchocerciasis highlights the need for more sensitive and specific methods that support programmatic assessments that can identify and combat recrudescence.