Methodology

Limitation of using synthetic human odours to test mosquito repellents

Fredros O Okumu^1,2,3 , Emmanuel Titus¹ , Edgar Mbeyela¹ , Gerry F Killeen^1,4,5 and Sarah J Moore^1,3,5

¹  Biomedical and Environmental Sciences Thematic group, Ifakara Health Institute, PO Box 53 Ifakara, Tanzania

²  School of Biological Sciences, University of Nairobi, PO Box 30197 Nairobi, Kenya

³  Disease Control and Vector Biology Unit, London School of Hygiene and Tropical Medicine, Keppel Street WC1E 7HT, London, UK

⁴  Vector group, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK

⁵  School of Biological Sciences, Durham University, South Road, DH1 3LE, Durham, UK

author email corresponding author email

Malaria Journal 2009, 8:150doi:10.1186/1475-2875-8-150

Published:	7 July 2009

Abstract

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.