Identification of human semiochemicals attractive to the major vectors of onchocerciasis.

Ryan M Young,Raymond Noblet,Eddie W Cupp,Mario A Rodriguez-Perez,Tommy W Mcgaha,Henry Fadamiro,Laurent D Toé,Charles R Katholi,Nathan D Burkett-Cadena,Thomas R Unnasch,Moussa Sanfo,Traore Soungalo,Mario C Salinas-Carmona,Bill Baker,Jose L Torres-Estrada,Monsuru A Adeleke,José M C Ribeiro

doi:10.1371/journal.pntd.0003450

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.

Highlights

Onchocerca volvulus, the etiological agent of ‘‘river blindness’’, remains a major public health threat in much of Africa and in a cross-border focus between Venezuela and Brazil [1]
Human landing collections, which are the current standard for collecting the black fly vectors of Onchocerca volvulus, the causative agent of river blindness, are inefficient and pose certain ethical issues
We report the use of electroantennography and behavioral assays to identify human compounds that are neurostimulatory to these vectors, and demonstrate that these compounds are attractive to the vectors in field studies using previously developed trap platforms. The development of such a defined bait formulation will permit the widespread use of these traps by onchocerciasis elimination programs in Africa and the Americas

Summary

Introduction

Onchocerca volvulus, the etiological agent of ‘‘river blindness’’, remains a major public health threat in much of Africa and in a cross-border focus between Venezuela and Brazil [1]. The World Health Organization and other international onchocerciasis elimination programs rely on measurement of the presence and intensity of transmission of the parasite for the verification of onchocerciasis elimination, both of which are measured by surveillance of the vector population [4]. Current methods to measure parasite transmission employ human landing collections to attract and collect vector black flies (Simulium spp.); infection data from the flies collected are . Entomological indicators are considered key metrics to document the interruption of transmission of Onchocerca volvulus, the etiological agent of human onchocerciasis. Recent studies reported the development of traps that have the potential for replacing humans for surveillance of O. volvulus in the vector population. The key chemical components of human odor that are attractive to vector black flies have not been identified

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