Identification of Human Semiochemicals Attractive to the Major Vectors of Onchocerciasis

Abstract

BackgroundEntomological indicators are considered key metrics to document the interruption of transmission of Onchocerca volvulus, the etiological agent of human onchocerciasis. Human landing collection is the standard employed for collection of the vectors for this parasite. Recent studies reported the development of traps that have the potential for replacing humans for surveillance of O. volvulus in the vector population. However, the key chemical components of human odor that are attractive to vector black flies have not been identified.Methodology/Principal FindingsHuman sweat compounds were analyzed using GC-MS analysis and compounds common to three individuals identified. These common compounds, with others previously identified as attractive to other hematophagous arthropods were evaluated for their ability to stimulate and attract the major onchocerciasis vectors in Africa (Simulium damnosum sensu lato) and Latin America (Simulium ochraceum s. l.) using electroantennography and a Y tube binary choice assay. Medium chain length carboxylic acids and aldehydes were neurostimulatory for S. damnosum s.l. while S. ochraceum s.l. was stimulated by short chain aliphatic alcohols and aldehydes. Both species were attracted to ammonium bicarbonate and acetophenone. The compounds were shown to be attractive to the relevant vector species in field studies, when incorporated into a formulation that permitted a continuous release of the compound over time and used in concert with previously developed trap platforms.Conclusions/SignificanceThe identification of compounds attractive to the major vectors of O. volvulus will permit the development of optimized traps. Such traps may replace the use of human vector collectors for monitoring the effectiveness of onchocerciasis elimination programs and could find use as a contributing component in an integrated vector control/drug program aimed at eliminating river blindness in Africa.

Identification of semiochemicals attractive to Simulium vittatum (IS‐7)

“…Only recently has more focused experimentation assessed electrophysiological and behavioural responses in two major blackfly vectors of O . volvulus [ Simulium ochraceum Walker, 1861 (complex) and S. damnosum Theobald, 1903 (complex)] to volatile organic compounds that may be involved in host‐seeking behaviour (Young et al ., ). That study used an array of organic compounds and demonstrated that only acetophenone, hexanal and cis‐3‐hexen‐1‐ol elicit an electrophysiological response in the two species complexes (Young et al ., ).…”

“…Electroantennography assays followed the procedures previously described (McGaha et al ., ; Young et al ., ). Briefly, blackfly samples were prepared in glass capillary tubes containing silver chloride‐coated electrodes (0.2 mm in diameter), of which one was connected to the tip of one antenna and the other was exposed to the internal tissues of the metathorax.…”

“…The compounds demonstrating activity in EAG were next tested for their attraction to host‐seeking S. vittatum females in a behavioural assay using a Y‐tube olfactometer model as previously described (Young et al ., ). Post‐oviposition flies were obtained from the colony and kept in an incubator at 25 °C and 70–90% RH until experiments were undertaken (i.e.…”

“…The attraction responses to each compound were assessed for each test run, and all compounds were tested using 10‐fold dilutions (1 : 10, 1 : 100, 1 : 1000 v/v; all of the compounds used in this phase were dissolved in hexane). The proportions of flies in the test and control arms were compared using a likelihood ratio test based on a multinomial probability model using a custom program written in fortran 95 (Young et al ., ). This program is available upon request.…”

The esperanza window trap reduces the human biting rate of Simulium ochraceum s.l. in formerly onchocerciasis endemic foci in Southern Mexico

“…volvulus transmission [8–11]. During field evaluations of the EWT, we observed that while black flies were attracted to workers that were setting up and maintaining the traps, the flies frequently diverted from those individuals and chose to land on the trap.…”