Limitation of using synthetic human odours to test mosquito repellents Fredros O Okumu*1,2,3, Emmanuel Titus1, Edgar Mbeyela1, Gerry F Killeen1,4,5 and Sarah J Moore1,3,5 Address: 1Biomedical and Environmental Sciences Thematic group, Ifakara Health Institute, PO Box 53 Ifakara, Tanzania, 2School of Biological Sciences, University of Nairobi, PO Box 30197 Nairobi, Kenya, 3Disease Control and Vector Biology Unit, London School of Hygiene and Tropical Medicine, Keppel Street WC1E 7HT, London, UK, 4Vector group, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK and 5School of Biological Sciences, Durham University, South Road, DH1 3LE, Durham, UK Email: Fredros O Okumu* - firstname.lastname@example.org; Emmanuel Titus - email@example.com; Edgar Mbeyela - firstname.lastname@example.org; Gerry F Killeen - email@example.com; Sarah J Moore - firstname.lastname@example.org * Corresponding author
Published: 7 July 2009 Malaria Journal 2009, 8:150 doi:10.1186/1475-2875-8-150
Received: 5 May 2009 Accepted: 7 July 2009
This article is available from: http://www.malariajournal.com/content/8/1/150 © 2009 Okumu et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: Gold-standard tests of mosquito repellents involve exposing human volunteers to host-seeking mosquitoes, to assess the protective efficacy of the repellents. These techniques are not exposure-free and cannot be performed prior to toxicological evaluation. It is postulated that synthetic lures could provide a useful assay that mimics in-vivo conditions for use in high-throughput screening for mosquito repellents. Methods: This paper reports on a semi-field evaluation of repellents using a synthetic blend of human derived attractants for the malaria vector, Anopheles gambiae sensu stricto Different concentrations of known repellents, N, N diethyl-3-methylbenzamide (deet) and Para-methane-3, 8, diol (PMD) were added into traps baited with the synthetic blend, and resulting changes in mosquito catches were measured. Results: All test concentrations of deet (0.001% to 100%) reduced the attractiveness of the synthetic blend. However, PMD was repellent only at 0.25%. Above this concentration, it significantly increased the attractiveness of the blend. There was no relationship between the repellent concentrations and the change in mosquito catches when either deet (r2 = 0.033, P = 0.302) or PMD (r2 = 0.020, P = 0.578) was used. Conclusion: It is concluded that while some repellents may reduce the attractiveness of synthetic human odours, others may instead increase their attractiveness. Such inconsistencies indicate that even though the synthetic attractants may provide exposure-free and consistent test media for repellents, careful selection and multiple-repellent tests are necessary to ascertain their suitability for use in repellent screening. The synthetic odour blend tested here is not yet sufficiently refined to serve as replacement for humans in repellent testing, but may be developed further and evaluated in different formats for exposure free repellent testing purposes.
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Malaria Journal 2009, 8:150
Personal protection with insect repellents is a popular method for preventing contact with arthropod disease vectors. While their modes of action may vary, repellents generally prevent host seeking vectors from landing on or biting the user. The vectors, which under normal circumstances would be attracted to the person, are either diverted away or disoriented in such a way that they fail to bite the host . These are...