<p>Abstract</p> <p>Background</p> <p>Removal of exhaled air from total body emanations or artificially standardising carbon dioxide (CO<sub>2</sub>) outputs has previously been shown to eliminate differential attractiveness of humans to certain blackfly (Simuliidae) and mosquito (Culicidae) species. Whether or not breath contributes to between-person differences in relative attractiveness to the highly anthropophilic malaria vector <it>Anopheles gambiae sensu stricto </it>remains unknown and was the focus of the present study.</p> <p>Methods</p> <p>The contribution to and possible interaction of breath (BR) and body odours (BO) in the attraction of <it>An. gambiae s.s. </it>to humans was investigated by conducting dual choice tests using a recently developed olfactometer. Either one or two human subjects were used as bait. The single person experiments compared the attractiveness of a person's BR versus that person's BO or a control (empty tent with no odour). His BO and total emanations (TE = BR+BO) were also compared with a control. The two-person experiments compared the relative attractiveness of their TE, BO or BR, and the TE of each person against the BO of the other.</p> <p>Results</p> <p>Experiments with one human subject (P<sub>1</sub>) as bait found that his BO and TE collected more mosquitoes than the control (P = 0.005 and P < 0.001, respectively), as did his BO and the control versus his BR (P < 0.001 and P = 0.034, respectively). The TE of P<sub>1 </sub>attracted more mosquitoes than that of another person designated P<sub>8 </sub>(P < 0.021), whereas the BR of P<sub>8 </sub>attracted more mosquitoes than the BR of P<sub>1 </sub>(P = 0.001). The attractiveness of the BO of P<sub>1 </sub>versus the BO of P<sub>8 </sub>did not differ (P = 0.346). The BO from either individual was consistently more attractive than the TE from the other (P < 0.001).</p> <p>Conclusions</p> <p>We demonstrated for the first time that human breath, although known to contain semiochemicals that elicit behavioural and/or electrophysiological responses (CO<sub>2</sub>, ammonia, fatty acids) in <it>An. gambiae </it>also contains one or more constituents with allomonal (~repellent) properties, which inhibit attraction and may serve as an important contributor to between-person differences in the relative attractiveness of humans to this important malaria vector.</p
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