Blackflies in the ointment: O. volvulus vector biting can be significantly reduced by the skin-application of mineral oil during human landing catches

BACKGROUND: Standard human landing catches (sHLCs) have historically been a key component of Onchocerca volvulus transmission monitoring, but expose health-workers to potentially hazardous vector bites. Novel human-bait-free trapping methods have been developed, but do not always work where they are needed and may not generate O. volvulus surveillance data that is directly comparable with historic data. METHODOLOGY: Simuliid sHLCs and mineral-oil protected HLCs (mopHLCs) were performed in a rural village of Amazonas state, Brazil. A four-hour direct comparisons of sHLCs and mopHLCs was carried-out using six vector collectors, each of whom used one leg for a sHLC and one for a mopHLC. Two-person collection teams then exclusively performed either mopHLCs or sHLCs for a further set of 12 four-hour collections. Following the completion of all collections, simuliid-bite mark estimates were made from legs used exclusively in sHLCs and legs used exclusively in mopHLCs. PRINCIPAL FINDINGS: All of the 1669 captured simuliids were identified as the O. volvulus vector Simulium oyapockense. Overall, mopHLC simuliids captured per hour (S/H) rates were lower than those obtained with sHLC trapping (15.5 S/H versus 20 S/H). Direct comparisons of simuliid capture rates found that vector-collectors captured simuliids significantly more efficiently ([Image: see text] : 20.5 S/H) with mopHLC trapping than with sHLC trapping ([Image: see text] : 16.4 S/H): P-value = 0.002. MopHLCs performed in isolation were, however, observed to capture vectors less efficiently ([Image: see text] : 13.4 S/H) than sHLCs performed under similar conditions ([Image: see text] : 19.98 S/H). All six vector collectors had significantly higher simuliid capture per counted bite mark (SC/CBM) rates using mopHLCs than they were observe to have using sHLCs ([Image: see text] : 21 SC/CBM versus [Image: see text] : 1 SC/CBM; p-value = 0.03125). CONCLUSIONS: Vector collectors captured significantly more simuliids per counted bite mark with mopHLCs than with sHLCs. Further investigations into the utility of mopHLCs for onchocerciasis xenomonitoring and beyond are merited.